ALBERT

Description: No abstract is available for this article.

Description: A new permanent ELF measurement station has been deployed in Sierra Nevada, Spain. It is composed of two magnetometers, oriented NS and EW, respectively. At 10 Hz, their sensitivity is 19 μ zV/pT and the Signal to Noise Ratio (SNR) is 28 dB for a time-varying signal of 1 pT, the expected field amplitude in Sierra Nevada. The station operates for frequencies below 24 Hz. The magnetometers, together with their corresponding electronics, have been specifically designed to achieve such an SNR for small signals. They are based on high-resolution search coils with ferromagnetic core and 10 6 turns, operating in limited geometry configuration. Different system noise sources are considered and a study of the SNR is also included. Finally, some initial Schumann resonance measurements are presented in order to validate the performance of the measurement station, including one hour length spectra, daily variations of resonance amplitudes and frequencies for the different seasons, and a three day spectrogram.

Description: Electromagnetic inspection techniques are becoming powerful tools for buried object detection and subsurface prospection in several applicative fields, such as civil engineering and archeology. However, the nonlinearity and ill-posedness of the underlying inverse problem make the development of efficient imaging techniques a very challenging task. In the present paper, an algorithm based on a regularizing approach in L p Banach spaces is proposed for tackling such problems. The effectiveness of the approach is verified by means of numerical simulations in a noisy environment, aimed at evaluating the reconstruction capabilities with respect to the choice of several model parameters. The reported results show that, for small targets, the use of L p Banach spaces with 1 〈  p  〈 2 allows to obtain a better localization of different buried scatterers.

Description: Using numerical simulations, we investigated a method for calculating the spectral parameters from Doppler spectra collected by high-resolution wind profiler radars (WPRs). Because high-resolution WPRs collect a huge amount of Doppler spectra, calculations must be simple and fast. The proposed method has two steps. In the first step, the echo range ( R echo ), in which the Doppler spectrum point with peak intensity is contained and all the smoothed Doppler spectrum points have intensities that are greater than the noise intensity, was determined. For producing the smoothed Doppler spectrum, a running average with equal weight (RA) or multi-taper method (MTM) was used. In the second step, the spectral parameters were calculated using the Doppler spectrum points within R echo . By comparing the performance of the computation methods using RA and MTM, we concluded that the computation method using RA is more suitable because it has better estimation performance for small spectrum widths and the calculations are faster. Estimation error of the spectral parameters depends on the determination accuracy of the Doppler spectrum peak and R echo . Furthermore, for the case of a 512-point Doppler spectrum and 13-point RA, the estimation errors tend to be independent of the signal-to-noise ratio (SNR) when the peak level of the Doppler spectrum ( p est ) is ~8 dB or more greater than the noise intensity. For p est of 〈 ~8 dB, the estimation errors are well correlated to p est and the SNR. Therefore, the number of incoherent integration times should be determined by considering the SNR and p est .

Description: Ionospheric total electron content (TEC) and atmospheric density perturbations were derived from measurements made from instruments onboard the Gravity Recovery and Climate Experiment (GRACE) spacecraft. At the time of the Tohoku-Oki earthquake on March 11, 2011, the twin spacecraft were orbiting at an altitude of ~450 km over Alaska. Significant TEC fluctuations (up to 0.6 TEC units), atmospheric density perturbations (~3.6 · 10 −14  kg/m 3 ), and sudden changes in GRACE acceleration (~4 · 10 −8  m/s 2 ) were observed ~8 minutes after the arrival of seismic and infrasound waves on the ground in Alaska, ~20 minutes after the Tohoku-Oki main shock at 05:46:23 UTC. The results of three-dimensional ionospheric-thermospheric modeling and infrasound ray-tracing simulations are consistent with the arrival time and physical characteristics of the disturbances at GRACE. This is the first time that ionospheric disturbances associated with an earthquake are clearly attributable to perturbations at such high altitudes.

Description: This paper offers an electromagnetic, more specifically array theory, perspective on understanding strong instrumental polarization effects for planar low-frequency “aperture arrays” with the Murchison Widefield Array (MWA) as an example. A long-standing issue that has been seen here is significant instrumental Stokes leakage after calibration, particularly in Stokes Q at high frequencies. A simple model that accounts for inter-element mutual coupling is presented which explains the prominence of Q leakage seen when the array is scanned away from zenith in the principal planes. On these planes, the model predicts current imbalance in the X (E-W) and Y (N-S) dipoles and hence the Q leakage. Although helpful in concept, we find that this model is inadequate to explain the full details of the observation data. This finding motivates further experimentation with more rigorous models that account for both mutual coupling and embedded element patterns. Two more rigorous models are discussed: the “full” and “average” embedded element patterns. The viability of the “full” model is demonstrated by simulating current MWA practice of using a Hertzian dipole model as a Jones matrix estimate. We find that these results replicate the observed Qleakage to approximately 2 to 5%. Finally, we offer more direct indication for the level of improvement expected from upgrading the Jones matrix estimate with more rigorous models. Using the “average” embedded pattern as an estimate for the “full” model, we find that Q leakage of a few percent is achievable.

Description: This paper deals with coherent processing of time reversal operator for microwave imaging in the frequency-domain. In frequency-domain time-reversal imaging approach, images obtained for different frequency bins over ultrawideband are incoherently processed. In highly dense and cluttered medium the signal subspace over each narrow frequency bin varies from that obtained using the complete ultrawideband. As a result, the detection and localization from non-coherent imaging approach is often inconclusive. In order to improve the stability of time-reversal microwave imaging, we propose coherent processing using novel focusing matrix approach. The proposed focusing matrix makes possible the time-reversal imaging technique to coherently process each frequency bin to yield a consistent signal subspace. The performance of coherent focusing is investigated when combined with time-reversal robust capon beamformer (TR-RCB). We have used numerical experiments on breast cancer detection using FDTD employing anatomically realistic numerical breast phantoms that contain varying amounts of dense fibro-glandular tissue content. The imaging results indicate that the proposed Coherent-TR-RCB (C-TR-RCB) could overcome the limitations of time-reversal imaging in a highly heterogeneous and cluttered medium.

Description: All-optical magnetic recording with localized circularly polarized light is studied for realizing ultra-fast and high-density magnetic recording. We design plasmonic cross antennas with bit-patterned media and evaluate the Stokes parameters. Using our proposed method, the magnetic recording speed is about 100,000 times faster than that for conventional methods and the recording density becomes over 2Tbit/inch 2 .

Description: In this study, a set of nine compact polarimetric (CP) images were simulated from polarimetric RADARSAT-2 data acquired over a test site containing two types of rice field in Jiangsu province, China. The types of rice field in the test site were (1) transplanted hybrid rice fields, and (2) direct-sown japonica rice fields. Both types have different yields and phenological stages. As a first step, the two types of rice field were distinguished with 94% and 86% accuracy respectively through analyzing CP SAR observations and their behavior in terms of scattering mechanisms during the rice growth season. The focus was then on phenology retrieval for each type of rice field. A decision tree (DT) algorithm was built to fulfill the precise retrieval of rice phenological stages, in which seven phenological stages were discriminated. The key criterion for each phenological stage was composed of 1–4 CP parameters, some of which were firstly used for rice phenology retrieval and found to be very sensitive to rice phenological changes. The retrieval results were verified at parcel level for a set of 12 stands of rice and up to nine observation dates per stand. This gave an accuracy of 88-95%. Throughout the phenology retrieval process, only simulated CP data was used, without any auxiliary data. These results demonstrate the potential of CP SAR for rice growth monitoring applications.

Description: This paper presents the effects of a weak geomagnetic storm event on January 17, 2013. While the Kp index reached a maximum of only 4, this event still caused severe disturbances for GNSS-based positioning services at high latitudes. We present data from the Norwegian Mapping Authority's Real Time Ionospheric Monitor (RTIM), based on a dense network of geodetic receivers, and scintillation indices from scintillation receivers located in Norway. In northern parts of Norway, the Centimeter positioning service (CPOS) was severely disturbed for hours. Service monitoring measurements showed that the effect was significantly worse for a receiver far away from the nearest network reference station.

Description: [1]  This paper addresses the coverage enhancement for broadband wireless access (BWA) at 800 and 3500 MHz in a rural scenario in north Germany using multi-hop relay concepts. The investigation is divided into two phases: In phase I, the coverage of a single BWA system in a rural area is predicted and verified with measurement data. In phase II, the coverage from the BWA system is analyzed and enhanced through the deployment of relay stations. The number of relay stations required for each carrier frequency is determined and the positions of the relay stations are identified via three different relay placement algorithms, namely path-loss-based, distance-based and hybrid algorithm. At 800 MHz, the path-loss-based algorithm requires 7 relay stations to achieve an overall coverage of 95 %. The hybrid and distance-based algorithms require 11 and 14 relay stations, respectively, to achieve the same coverage. At 3500 MHz, path-loss based and hybrid algorithm require 19 and 16 relay stations, respectively, to achieve the same coverage. The distance-based requires 20 relay stations to achieve an overall coverage of 82 % at 3500 MHz. Further increase of relay stations has led to higher interference hence the overall coverage of 95 % can never be reached using the distance-based algorithm at 3500 MHz. Lastly, the transmit power of the relay station is optimized via an intelligent power allocation scheme. The results show that 20 % of the total transmit powers from 14 relay stations can be saved at 800 MHz whereas 18 % of the total transmit powers from the 20 relay stations can be saved at 3500 MHz.

Description: [1]  A real-time ionospheric mapping system is tested to investigate its ability to compensate for the ionospheric delay in single-frequency Global Positioning System (GPS) time transfer over Europe. This technique is compared with two other single-frequency systems: one that does not incorporate any ionospheric correction and one that uses the broadcast Klobuchar model. A dual-frequency technique is also shown as a benchmark. A period in March 2003, during a solar maximum, has been used to display results when the ionospheric delays are large and variable. Data from two European GPS monitoring centres were used to test the time-transfer methods. For averaging times between several minutes and a few hours, the instabilities in the time transfers were dominated by ionospheric effects. The instabilities at longer averaging times were found to be due to clock noise and hardware instabilities. Improvements in time transfer instabilities are shown by using the ionospheric tomography system.

Description: [1]  Spectra and the waveforms are computed of the pulsed radio signals arriving from different distances to an observer in the Earth–ionosphere cavity with the single scale exponential profile of air conductivity. The data were obtained for the cavity with exceptionally small losses. Spectra are compared of the signals in the realistic and an idealistic Earth – ionosphere cavities. The waveforms are computed for such cavities and the pulse propagation velocities are evaluated. Studies of the Schumann resonance started from the ideal cavity model. Subsequent works dealt with the realistic propagation parameters and the ionosphere models on the Earth and other planets. However, the case of small losses is missing in the literature. We model ELF radio signals in such a cavity and demonstrate their noticeable distinctions from the customary records. In particular, the sinusoidal signals do not appear in the cavity with small losses, and instead we obtain the sharp and large pulses. Computations show that the waveform propagating in the spherical cavity expands in time and reduces in amplitude. The time domain pulsed amplitudes were found at the source antipode and at the source point for the round-the-world wave. The latter becomes rather small even in the cavity with minor losses, so that auto-triggering is unrealistic of a consecutive lightning discharge by the round-the-world echo even in a cavity with minor losses.

Description: A method for foF2 short-term forecast over Europe has been developed and implemented in the EUROMAP model, which is used in operational systems. The input driving parameters are 3-hour ap indices (converted to the accumulative index ap(τ) ), effective ionospheric T-index, and real-time foF2 observations. The method includes local (for each station) regression storm models to describe strong negative disturbances under ap(τ)  〉 30 and training over previous 28-day models to describe foF2 variations under ap(τ) ≤ 30. Index T is used to specify the background level. The derived model was tested in two regimes: descriptive when observed 3-hour ap indices were used and real forecast when predicted daily Ap were used instead of 3-hour ap indices – daily Ap is the only geomagnetic index which is predicted at present with (1-3) day lead time. In the case of strong negative disturbances (the descriptive regime) the EUROMAP model demonstrates on average the improvement over the IRI(STORM) model: 40% in Winter, 24% in Summer, and 39% in Equinox. The average improvement over climatology is 41% in Winter, 59% in Summer, and 55% in Equinox. In the majority of cases this difference is statistically significant (≥ 95%) according to Student criterion. In the case of strong positive disturbances, higher latitude stations (Moscow, Juliusruh, Slough) also manifest a significant difference between the two models but this difference is insignificant at lower latitude stations (Athens, Rome, Tortosa). The substitution of observed 3-hour ap input indices for the predicted daily Ap ones (the forecast regime) decreases the prediction accuracy in the case of negative disturbances but practically has no effect on the foF2 prediction accuracy with positive disturbances. In both cases the proposed method manifests better accuracy than the IRI(STORM) model provides although this difference sometimes statistically is not significant (〈 95%). The obtained results show a real opportunity to provide foF2 forecast with the (1-24) h lead time on the basis of predicted Ap indices.

Description: [1]  A new capability for high-sensitivity, all-sky monitoring of VHF meteor-trail reflections with the first station of the Long Wavelength Array, or “LWA1,” is described. LWA1 is a ∼ 100m-diameter HF/VHF array of 256 crossed-dipole antennas with a unique transient buffer mode that allows it to monitor for meteor trails via all-sky imaging with the same sensitivity as a single-dish antenna m in diameter. To demonstrate this capability, we have used a two-hour observing run conducted in August 2012 aimed at detecting and characterizing meteor-trail reflections of analog TV transmissions at 55.25 MHz. The analysis techniques described here allowed for a detection rate of ∼9,500 trails per hour, including the detection of two meteor streams with radiants in the Aries/Perseus and Aquila/Hercules regions that were not previously reported in the literature. In addition, we have found a population of relatively long-duration (∼ 1 to a few minutes), typically fainttrails. These trails have implied horizontal speeds of 15–130 m s − 1 , with a typical speed of ∼30 m s − 1 . We have also used high-resolution time series of the brightest trails to characterize decay times over a relatively large geographical area (10 ∘  × 7 ∘ in longitude and latitude) and on short (∼5 minutes) time scales. Potential enhancements that could be enabled by the addition of more LWA stations are discussed.

Description: [1]  The STEREO/WAVES experiment (SWAVES) onboard the two STEREO spacecraft (Solar TErrestrial RElations Observatory) launched on Oct 25, 2006, is dedicated to the measurement of the radio spectrum at frequencies between a few kHz and 16 MHz. The SWAVES antenna system consists of 6 m long orthogonal monopoles designed to measure the electric component of the radio waves. With this configuration direction finding of radio sources and polarimetry (analysis of the polarization state) of incident radio waves is possible. For the evaluation of the SWAVES data the receiving properties of the antennas, distorted by the radiation coupling with the spacecraft body and other onboard devices, have to be known accurately. In the present context, these properties are described by the antenna effective length vectors. We present the results of an in-flight calibration of the SWAVES antennas using the observations of the non-thermal terrestrial Auroral Kilometric Radiation (AKR) during STEREO roll maneuvers in an early stage of the mission. A least squares method combined with a genetic algorithm was applied to find the effective length vectors of the STEREO-B/WAVES antennas in a quasi-static frequency range ( L antenna  ≪  λ wave ) which fit best to the model and observed AKR intensity profiles. The obtained results confirm the former SWAVES antenna analysis by rheometry and numerical simulations. A final set of antenna parameters are recommended as a basis for evaluations of the SWAVES data.

Description: [1]  In a previous study we developed an elegant technique to compute the signal travel time delay due to the neutral atmosphere, also known as Slant Total Delay (STD), between a Global Positioning System (GPS) satellite and a ground-based receiver utilizing data from a Numerical Weather Model (NWM). Currently, we make use of NWM data from the Global Forecast System (GFS) because short range forecasts are easily accessible. In this study we introduce some modifications which double the speed of our algorithm without altering its precision; on an ordinary PC (using a single core) we compute about 2000 STDs per second with a precision of about 1 mm. The data throughput and precision are independent of the vacuum elevation (azimuth) angle of the receiver satellite link. Hence the algorithm allows the computation of STDs in a meso-beta scale NWM with an unprecedented speed and precision. A practical by-product of the algorithm is introduced as well; the Potsdam Mapping Factors (PMFs), which are generated by fast direct mapping utilizing short range GFS forecasts. In fact, it appears that the PMFs make the application of parameterized mapping in GPS processing obsolete.

Description: [1]  Ray tracing data is usually given as a vector of many variables, such as angles of arrival and departure, transmitter and receiver coordinates, ray length and delay, received power level, and polarity. Usually, these values are given in raw data with some resolution that covers the area of interest where the simulation is performed. There are two main drawbacks of such approach; firstly a huge amount of storage capacity is typically needed to store all necessary data and secondly, although the area of interest is covered by a certain resolution, it is not straightforward, but rather nearly impossible to interpolate between sample points and new time and memory consuming simulations are necessary in order to increase the resolution of simulations. This paper addresses the two mentioned drawbacks of ray tracing, suggesting a procedure based on the concept of ray entities to both enable continuous interpolation of ray tracing data and reduce memory needed for storing data. Ray entity is a set of rays that all undergo the same series of propagation phenomena (direct ray, diffraction, reflection or scattering) on the same objects (building walls or edges). The method is given and illustrated for reflection and diffraction phenomena and diffuse scattering was not included, but discussion is easily extended to this propagation type as well. The paper gives detailed statistics of entities’ length and rays’ count per simulated receiver point in few illustrative examples and provides an insight into how to interpolate angles of arrival and departure, ray length and received power level in order to provide continuous description of the radio environment.

Description: In this article a radial basis function (RBF) neural network improved by Gaussian mixture model (GMM) is developed to be used for forecasting ionospheric 30-min total electron content (TEC) data given the merits of its nonlinear modeling capacity. In order to understand more about the response of developed network model with respect to stations situated at different latitude, estimated TEC overhead of GPS ground stations BJFS (39.61°N, 115.89°E), WUHN (30.53°N, 114.36°E) and KUNM (25.03°N, 102.80°E) for six months in 2011 are used for training dataset, validating data and test dataset of RBF network model. The performance of the trained model is evaluated at a set of criteria. Our results show that the predicted TEC is in good agreement with observations with mean relative error of about 9% and root mean square error of less than 5 TECU. Our comparison further indicates that RBF network offers a powerful and reliable tool for the design of ionospheric TEC forecast.

Description: In radio system deployment the main focus is on assuring sufficient coverage, which can be estimated with pathloss models for specific scenarios. When more detailed performance metrics such as peak throughput are studied, the environment has to be modeledaccurately in order to estimate multipath behavior. By means of laser scanning we can acquire very accurate data of indoor environments, but the format of the scanning data, a point cloud, cannot be used directly in available deterministic propagation prediction tools. Therefore we propose to use a single-lobe directive model, which calculates the electromagnetic field scattering from a small surface and is applicable to the point cloud, and describe the overall field as fully diffuse back-scattering from the point cloud. The focus of this paper is to validate the point cloud-based full-diffuse propagation prediction method at 60 GHz. The performance is evaluated by comparing characteristics of measured and predicted power delay profiles in asmall office room and an ultrasonic inspection room in a hospital. Also directional characteristics are investigated. It is shown that by considering single-bounce scattering only, the mean delay can be estimated with an average error of 2.6 % and the rms delay spread with an average error of 8.2 % . The errors when calculating the azimuth and elevation spreads are 2.6 ∘ and 0.6 ∘ , respectively. Furthermore the results demonstrate the applicability of a single parameter setto characterize the propagation channel in all transmit and receive antenna locations in the tested scenarios.

Description: No abstract is available for this article.

Description: The inherent difficulties of traditional preconditioning techniques are revealed by numerically analyzing characteristics of method of moments (MoM) systems with respect to multiscale dynamic electromagnetic applications. Techniques are developed to solvethese difficulties for the traditional sparse approximate inverse (SAI) preconditioner. The proposed techniques includes a skeleton-based filtering strategy aiming to overcome the awkward filtering strategy extensively employed in traditional preconditioners and the strategy to recover the block structure of the inverse matrix. The proposed techniques are investigated by numerical experiments on complex targets.

Description: Total electron content (TEC) is an important parameter for revealing latitudinal ionospheric structures, such as the equatorial ionization anomaly (EIA) in Southeast Asia. Understanding the EIA is beneficial for studying equatorial spread F . To reveal the structures, the absolute TEC as a function of latitude must be accurately determined. In early 2012, we expanded a GNU Radio Beacon Receiver (GRBR) network to provide latitudinal coverage in the Thailand-Indonesia sector. We employed the GRBR network to receive VHF and UHF signals from polar low-Earth-orbit satellites. The TEC offset is an unknown parameter in the absolute TEC estimation process. We propose a new technique based on the two-station method to estimate the offset for the latitudinal TEC estimation, and it works better than the original method for a sparse network. The TEC estimation system requires two iterations to minimize the root-mean-square error (RMSE). Once the RMSE reaches the global minimum, the absolute TECs are estimated simultaneously over five GRBR stations. GPS-TECs from local stations are used as the initial guess of the offset estimation. The height of the ionospheric pierce point is determined from the ionosonde hmF2. As a result, the latitudinal GRBR-TEC was successfully estimated from the polar orbit satellites. The two EIA humps were clearly captured by the GRBR-TEC. The result was well verified with the TEC reconstructed from the C/NOFS density data and the ionosonde bottomside data. This is a significant step showing that the GRBR is a useful tool for the study of low-latitude ionospheric features.

Description: It has long been known that thunderstorms produce strong electric field fluctuations in their immediate vicinity but it has been little recognized that these storms can also be a source of strong ULF magnetic field fluctuations (ULF; frequencies less than 5 Hz). Some characteristics of these magnetic field fluctuations were documented for a thunderstorm occurring in 1990 [Fraser-Smith, Geophys . Res . Letts ., 467–470, 1993]. We now describe further measurements of these magnetic field changes for a well-defined and comparatively intense thunderstorm that passed over the San Francisco Bay area on 8–9 September 1999. The thunderstorm is further characterized by measurements of its associated lightning by the National Lightning Detection Network (NLDN). As compared with the results reported for the 1990 thunderstorm, the new measurements were made by two independent systems and more components of the magnetic field changes are measured. Given the possibility that the thunderstorm-related ULF magnetic field changes can stimulate ULF hydromagnetic waves in the ionosphere, these measurements suggest, once again, that thunderstorms may be a source of ULF energy in the magnetosphere that can, in turn, lead to the generation of some of the ULF geomagnetic pulsations commonly observed on the ground. In addition, it may also be significant that the frequencies associated with these hydromagnetic waves in the magnetosphere are ideally suited for them to interact with some populations of the protons and ions in the radiation belts, potentially inducing them to precipitate into the atmosphere.

Description: We introduce a new coherent dual channel beacon satellite receiver intended for ionospheric tomography. The measurement equation includes neutral atmosphere and ionosphere propagation effects, relative errors in satellite and receiver clocks, and residual Doppler shifts caused by errors in the satellite ephemeris. We also investigate the distribution of errors for phase curve measurements and the use of phase curve measurements for limited angle tomography using the framework of statistical linear inverse problems. We describe the design of our beacon satellite receiver software, and present one possible hardware configuration. Finally, we present results obtained using a network of four newly developed receivers and compare the results with those of an existing ionospheric tomography network at Sodankylä Geophysical Observatory.

Description: We present analytical closed-form expressions for the radiation patterns of 2D line sources and 3D point dipoles embedded in a general multi-layered configuration. While the former are simplified model sources, used as a preliminary analytical step toreduce derivation complexity, the latter have been shown experimentally to reproduce the electromagnetic behaviour of many elementary statistical sources. By decomposing the sources to current elements generating pure transverse electric (TE) or transverse magnetic (TM) polarized radiation, we arrive at a unified format for the radiation pattern expression for all sources considered. Analyzing the common 1D (characteristic) Green's function, we show that the normalized TE-polarized emission of model 2D electric line sources reproduces exactly the measured TE-polarized radiation of statistical (3D) dipoles with random in-plane orientation; the connection between the TM-polarized emission of the two species is discussed, and physical interpretation is provided via the unified expression. These results specify the precise relations between the 2D and 3D models, providing intuition as well as guidelines for proper usage of simplified 2D results for analysis of realistic 3D statistical configurations.

Description: A GNU Radio Beacon Receiver (GRBR) system for Total Electron Content (TEC) measurements using 150 and 400 MHz transmissions from Low-Earth Orbiting Satellites (LEOS) is fabricated in-house and made operational at Ahmedabad (23.04°N, 72.54°E geographic, dip latitude 17°N) since May 2013. This system receives the 150 and 400 MHz transmissions from high inclination LEOS. The first few days of observations are presented in this work to bring out the efficacy of an ensemble average method to convert the relative TECs to absolute TECs. This method is a modified version of the differential Doppler based method proposed by de Mendonca [1962] and suitable even for ionospheric regions with large spatial gradients. Comparison of TECs derived from a collocated GPS receiver shows that the absolute TECs estimated by this method are reliable estimates over regions with large spatial gradient. This method is useful even when only one receiving station is available. The differences between these observations are discussed to bring out the importance of the spatial differences between the ionospheric pierce points of these satellites. A few examples of the latitudinal variation of TEC during different local times using GRBR measurements are also presented, which demonstrates the potential of radio beacon measurements in capturing the large-scale plasma transport processes in the low latitude ionosphere.

Description: The global precipitation measurement mission is an international satellite mission to obtain accurate observations of precipitation on a global scale every three hours. The GPM core satellite was launched on Feb 27, 2014 with two science instruments: themicrowave imager and the dual frequency precipitation radar. Ground validation is an integral part of the GPM mission where instruments are deployed to complement and correlate with spacecraft instruments. The dual-frequency, dual-polarization, Doppler Radar (D3R) is a critical ground validation instrument that was developed for the GPM program. This paper describes the salient features of the D3R in the context of the GPM ground validation mission. The engineering and architectural overview of the radar is described and observations from successful GPM ground validation field experiments are presented.

Description: We describe herein a measurement of the Antarctic surface “roughness” performed by the balloon-borne ANITA (ANtarctic Impulsive Transient Antenna) experiment. Originally purposed for cosmic-ray astrophysics, the radio-frequency (RF) receiver ANITA gondola, from its 38 km altitude vantage point, can scan a disk of snow surface 600 km in radius. The primary purpose of ANITA is to detect RF emissions from cosmic rays incident on Antarctica, such as neutrinos which penetrate through the atmosphere and interact within the ice, resulting in signal directed upwards which then refracts at the ice-air interface and up and out to ANITA, or high-energy nuclei (most likely irons or protons), which interact in the upper atmosphere (at altitudes below ANITA) and produce a spray of down-coming RF which reflects off the snow surface and back up to the gondola. The energy of such high-energy nuclei can be inferred from the observed reflectedsignal only if the surface reflectivity is known. We describe herein an attempt to quantify the Antarctic surface reflectivity, using the Sun as a constant, unpolarized RF source. We find that the reflectivity of the surface generally follows the expectations from the Fresnel equations, lending support to the use of those equations to give an overall correction factor to calculate cosmic ray energies for all locations in Antarctica. The analysis described below is based on ANITA-II data. After launching from McMurdo Station in December, 2008, ANITA-II was aloft for a period of 31 days with a typical instantaneous duty cycle exceeding 95%.

Description: The progress in the development of thin and lightweight artificial absorbers has revived interest in approaches to simulation of electromagnetic scattering from electrically large low reflection bodies. The absorbers, irrespective of their interior structure, can be often adequately described by an equivalent surface impedance which is matched with the wave impedance of the surrounding medium. As full-wave simulations of scattering from electrically large curved surfaces with underlying dense arrays of sub-wavelength inclusions are hardly possible, the main candidate is the physical theory of diffraction (PTD), adjusted to the use of impedance boundary conditions with the matched surface impedance. The paper describes a suitable PTD formulation with a focus on edge corrections.

Description: Ground-based radiometric techniques were applied to measure the slant path attenuation cumulative distribution function to over 20 dB of attenuation and to less than 1% exceedance probability at the V and W band frequencies of 72.5 and 82.5 GHz. These are the first such measurements in these frequency bands. Brightness temperature measurements were collected at an elevation angle of 36° in Rome NY using a four-channel radiometer that included 23.8 and 31.4 GHz receivers. A model based approach was used to invert brightness temperature to attenuation. An atmospheric model relevant to the geographic location and statistically representative of the attenuating conditions was developed for this purpose. The main assumption of the atmospheric model was that the sources of attenuation for exceedance probabilities of concern were dominated by stratiform rain. Monte-Carlo solutions to the radiative transfer equation for the precipitating atmosphere were used to generate the attenuation retrieval algorithm. Sensitivity analysis showed that the attenuation retrieval algorithm was robust to uncertainties in the model parameters. Slant path attenuation was also measured with the radiometer using the sun as a source of radiation. Over 30 dB of attenuation dynamic range was possible with this technique. Sun-beacon measurements were used to test model predictions.

Description: An algorithm has been developed to image the local structure in the convection electric field using multi-beam incoherent scatter radar (ISR) data. The imaged region covers about 4 ° in magnetic latitude and 8 ° in magnetic longitude for the specific geometry considered (that of the Poker Flat ISR). The algorithm implements the Lagrange method of undetermined multipliers to regularize the underdetermined problem posed by the radar measurements. The error on the reconstructed image is estimated by mapping the mathematical form to a Bayesian estimate, and observing that the Lagrangian method determines an effective a priori covariance matrix from a user-defined regularization metric. There exists a unique solution when the average measurement error is smaller than the average measurement amplitude. The algorithm is tested using synthetic and real data, and appears surprisingly robust at estimating the divergence of the field. Future applications include imaging the current systems surrounding auroral arcs in order to distinguish physical mechanisms.

Description: We have used Total Electron Content (TEC) derived from dual frequency GPS receivers to study magnetically quiet and storm time variations of the ionosphere at Ilorin(8.47°N, 4.68°E), an equatorial station in the Africa sector. Four years (2009-2012) data were used for the study. The result on the quiet-time variation of the ionosphere showed that diurnal variation of TEC is not symmetrical about noon. This is a departure from a typical Chapman variation. Daytime maximum occurred after local noon (13-16 LT) for all the seasons and at all solar activity levels considered. A significant effect of solar activity variation was observed on the seasonal trend in 2011. The tendency for magnetic storms to cause increases in TEC is much greater than those of decreases. Daytime maximum TEC usually occurred closer to the noon time during storm periods when compared to those of quiet periods. Maximum percent change in TEC on storm days varied from about 25 to 131 percent.

Description: This paper presents an ionosphere scintillation mapping algorithm. The technique used is a Kriging technique, well known in geostatistics. It is an interpolation method applied to a set of random data, namely in this application, to the intensity scintillation (S4) index. The paper focuses on the importance of the regression model used in the algorithm. The one dimension, then the two dimensions problem have been investigated. One example of results combining measurement data recorded by two different networks in Peru is presented. The accuracy of the results has been verified using a cross validation technique, which consists in removing part of the known dataset and comparing the interpolated results to it.

Description: There are a variety of methods employed for determination of phase and amplitude scintillation on satellite signals which generally employ different models and theory. The paper shows that in spite of this very similar results can be found in most circumstances for 4 different methods for a very wide range of physical input parameters for weak scintillation conditions. Further comparison between results for different methods can help to determine their modelling errors and hence can also lead to more accurate determinations using improved models.

Description: This contribution presents a model to generate time series of rain attenuation by adapting a large set of rain attenuation measurements to different locations. The proposed model allows generating rainy and not rainy conditions for multiple stations in a large geographical area, reproducing the actual spatial and temporal variability of the rain process, with limited computational effort. Single site and joint statistics of rain attenuation obtained by the time series of measurements are discussed. The model is used to show the effectiveness, in terms of link margin, of gateway networks in smart diversity arrangement, for different separation distances among sites.

Description: Transionospheric satellite navigation links operate primarily at L-band and are frequently subject to severe degradation of performances arising out of ionospheric irregularities. Various characteristic features of equatorial ionospheric irregularity bubbles like the drift velocity, characteristic velocity, decorrelation time and decorrelation distance can be determined using spaced aerial measurements at VHF. These parameters measured at VHF from a station Calcutta situated near the northern crest of the Equatorial Ionization Anomaly (EIA) in the geophysically sensitive Indian longitude sector have been correlated with L-band scintillation indices and GPS position accuracy parameters for identifying possible proxies to L-band scintillations. Good correspondences have been observed between decorrelation times and distances at VHF with GPS S 4 and PDOP during periods of GPS scintillations (S 4  〉 0.3) for February-April 2011, August-October 2011 and February-April 2012. A functional relation has been developed between irregularity drift velocity measured at VHF and S 4 at L-band during February-April 2011, and validation of measured S 4 and predicted values performed during August-October 2011 and February-April 2012. Significant improvement in L-band scintillation prediction and consequent navigational accuracy will result using such relations derived from VHF irregularity measurements which are much simpler and inexpensive.

Description: Radio systems are affected by rainfall and the attenuation increases significantly with rain rate and frequency. Above about 10 GHz rainfall must generally be considered for estimating expected link availability and sufficient attenuation margin included. Rain rate is a key factor and depending on climate it will dictate the possible path length and other factors such as antenna size, for wanted performance of a system that operates at higher frequencies than about 10 GHz. This paper presents results from an analysis of Norwegian tipping bucket rain gauge data from 1967 through 2013. It is found that the rain rate currently used by ITU-R recommendation for attenuation prediction, R 0.01 - the rate exceeded for 0.01% of an average year - has actually increased in all parts of the country from where long term data exist. Moreover, the year to year variability is significant. The increase may well be seen as a consequence of climate change. Such a change may cause higher attenuation effects than expected when radio links are designed following " normal" dimensioning procedures.

Description: Long range propagation of heater-produced signals has been studied in experiments with EISCAT (the European Incoherent Scatter Scientific Association) ionospheric heating facility and with several globally distributed receiving sites by Zalizovski et al. (2009). Two distinctive components were present in the signals’ spectra and these can be attributed to two modes of propagation of the signals. One of the components is narrowband and stable; it obviously can be associated with the multihop ionospheric propagation of HF waves radiated by the side lobes of the heater's antenna array. Prominent features of the second component are its wider spectral band (up to few tens Hz) and strong variations in the average Doppler frequency shift and in the power, which in many cases were synchronous at the different receiving sites. These effects are most likely produced by the ionospheric scattering and dynamics within the heater's main beam. The tricky part is to explain how a portion of the HF energy contained in the relatively narrow main beam of the heater is redirected towards the remote receiving locations. We suggest a robust mechanism explaining the long-range propagation of the wide-band component of the heater-generated signal based on the theory of scattering from rough surfaces. This mechanism preserves all the observed properties of the remote signals. We show that mountain relief in the vicinity of the heater plays the role of the rough surface causing almost isotropic scattering of the heater's main beam after it is reflected by the ionosphere. Multiple scattering by natural and artificial field-aligned irregularities in the ionospheric layer may be related to the ground-scattered remote signals through its role in spatial redistribution of the heater's radiation.

Description: This paper deals with the detection and quantification of refractivity turbulence in the troposphere from radiosonde and Very High Frequency (VHF)-band radar data. Balloon data processing methods based on Thorpe sorting and recently developed by Wilson et al. [2010, 2011, 2013] can be applied for a direct identification of turbulent layers from the in situ profiles. The VHF-band mid- and upper atmosphere radar (MUR) can be operated in range-imaging mode for detecting and monitoring turbulent layers at high time and range resolutions (of the order of 10 sec and a few tens of meters, respectively). For cross-validating the techniques, concurrent MUR and RS92-SGP Vaisala radiosonde observations were made at the Shigaraki Middle and Upper atmosphere (MU) observatory (34.85 N, 136.15E; Japan) during a field campaign of three weeks in September 2011. The radar signature, in terms of echo power and aspect ratio, of the turbulent layers identified from balloon data analyses is investigated from case studies and statistics. The deep (〉 ~ 100 m) layers are very often associated with echo power maxima and weak aspect ratios suggesting that the same events of isotropic turbulence were detected by both instruments. Some others are associated with relative minima of isotropic echo power, possibly indicating a latter stage of turbulence. The ranges of strong aspect ratios are generally not associated with turbulent events in the balloon data supporting the hypothesis that anisotropic turbulence is not the cause of vertically enhanced radar echoes. Quantitative comparisons are made between radar echo power and refractive index constant structure  estimated from temperature variance and additional parameters in the selected layers. Despite a large scatter between the radar and balloon estimates, the results are statistically significant (correlation coefficients ~0.5-0.88) even when the causes of systematic decrease with height of Cn2 (humidity and density) are removed. Our studies therefore demonstrate that radar and balloon observations of turbulence are consistent between each other and that new insights on tropospheric turbulence can be obtained by the two techniques as stand-alone systems.

Description: Sum-of-cisoids (SOC) processes provide an important framework for the modelling and simulation of multipath fading channels. In this paper, we analyse the performance of SOC Rice/Rayleigh narrowband fading channel simulators with respect to the bit error probability (BEP) of quadrature phase shift keying (QPSK) and differential phase shift keying (DPSK) systems with both coherent and noncoherent demodulation. For the BEP of coherent QPSK and DPSK, exact analytical expressions are derived, which provide insight into the influence of the number of propagation paths and the path gains on the system performance. It will be shown that at least 10 multipath components are required to guarantee that the absolute value of the relative error of the BEP is less than 5 per cent. Regarding the BEP of noncoherent DPSK, we show analytically and by simulations that the system performance reacts very sensitively to the model error caused by an imperfect computation of the channel simulator's Doppler frequencies. Our study is not only important for the performance evaluation of SOC-based channel simulators but also for the performance evaluation of QPSK and DPSK systems in the presence of a limited number of scatterers. Especially for asmall number of propagation paths with unbalanced path gains, where the central limit theorem does not apply, the derived analytical expressions for the BEP reveal their full importance.

Description: As described in a previous paper [ Tsai et al ., 2009], a three-dimensional ionospheric electron density ( N e ) model has been constructed from vertical N e profiles retrieved from the FS3/COSMIC GPS radio occultation (RO) measurements and worldwide ionosonde foF2 and foE data, and named the TaiWan Ionospheric Model (TWIM). The TWIM exhibits vertically fitted α-Chapman-type layers with distinct F2, F1, E, and D layers, and surface spherical harmonic approaches for the fitted layer parameters including peak density, peak density height and scale height. To improve the TWIM into a real-time model we have developed a time series autoregressive model to forecast short-term TWIM coefficients. The time series of TWIM coefficients are considered as realizations of stationary stochastic processes within a processing window of 30 days. These autocorrelation coefficients are used to derive the autoregressive parameters and then forecast the TWIM coefficients, based on the least squares method and Lagrange multiplier technique. The forecast root-mean-square relative TWIM coefficient errors are generally 〈30% for one day predictions. The forecast TWIM values of foE and foF2 values are also compared and evaluated using worldwide ionosonde data.

Description: Rainfall rate varies both temporarily and spatially. Radio systems where rain attenuation causes outages, may take advantage of this effect to increase the radio link or satellite link availability using diversity techniques. In the Oslo region with Norwegian Meteorological Institute located at Blindern, there are 24 tipping bucket rain gauges within 50 km radius of the institute where each station has 5 years or more of simultaneous data periods with the station at the institute. The simultaneous data have been used to calculate spatial rain rate correlation and derive a prediction method based on separation distance and orientation with respect to dominating weather direction. Part of joint rain rate distribution was fitted to lognormal to find the measured correlation coefficients. In addition an analysis of independent radiosonde data suggest that prevailing wind at 700 hPa or 850 hPa altitude (approximately 3000 m or 1500 m above sea level) conditioned thunderstorm index in the range 15 to 20, may be used to identify the actual rainfall movement or dominant weather direction. Compared with current recommended method by ITU-R the new method gives an improved site diversity prediction judged by site selection of minimum 20 GHz attenuation data measured in 2012 from earth stations located at Nittedal and Kjeller separated by 23 km.

Description: Basic theory of matrix equilibration is presented, relating it to other techniques for decreasing the condition number of matrix equations obtained by the method of moments (MoM) applied to surface integral equations (SIEs). It is shown that matrix equilibration is a general technique that can be used for both: 1) balancing field and source quantities in SIEs, which is used to decrease the condition number in the case of SIEs of mixed type and high contrast in material properties, and 2) scaling basis and test functions in MoM, which is used to decrease the condition number in the case of higher order bases and patches of different sizes. In particular, it is demonstrated that a combination of such balancing and scaling can be performed using simple matrix equilibration based on magnitudes of diagonal elements and 2-norms of rows/columns of the MoM matrix.

Description: After defining a continuum using rigorous spatial-dispersion equations for the macroscopic, fundamental Floquet modal fields of 3D periodic metamaterial arrays, boundary conditions are derived for electric quadrupolar continua under the assumption that the electric quadrupolarization density contains no extra delta functions within the interface transition layer (in addition to the delta function that usually occurs in the divergence of the electric quadrupolarization across the interface). A physically reasonable constitutive relation, in which the electric quadrupolarization density is proportional to the spatial derivatives of the electric field, is used to examine this assumption and the applicability of the boundary conditions. It is found that, although extra delta functions can be produced by a TM plane wave incident upon an interface, the boundary conditions remain essentially unaffected by these extra delta functions for small enough electrical separation distances between the inclusions of the arrays.

Description: The power budget of a wireless link between two electrically small sensor nodes located close to an interface between two media is studied. The model includes both the propagation channel losses and input impedance of the radio-frequency antennas. It isshown that a highly inductive half-space significantly enhances the received power due to the contribution of the surface wave while not resulting in considerable mismatch losses between the antennas and electronics. Hence, such a half-space improvesthe link gain, which may compensate the limited energy available for transmission from electrically and physically small nodes.

Description: Global Positioning System (GPS) time and frequency transfer is one of the most useful ways for the comparison of remote clocks, and the comparison results are very important for the calculation of TAI (International Atomic Time) and UTC (Coordinated Universal Time). For the timing laboratories, it is necessary to calibrate and periodically evaluate their time transfer system to ensure the accuracy and long term stability of their time and frequency comparison results. Once the calibration is achieved, it can be used as a standard for traceable time and frequency measurements. In this paper, we demonstrate Global Navigation Satellite System (GNSS) receiver calibration campaign between the National Time and Frequency Standard Laboratory of Telecommunication Laboratories (TL) in Taiwan and the Measurement Standards Laboratory (MSL) in New Zealand. Two calibration strategies, receiver calibration and the link calibration, are adopted in this work. The receiver calibration is used for evaluating the performance of the proposed system in domestic traceability network in Taiwan. The link calibration is used for minimizing the total uncertainty budget in calculating UTC. Experimental results indicate that the expanded time and frequency uncertainty of the proposed system (with a coverage factor of k = 2) are less than 25 ns and 1.1 x10 -13 , respectively after 1 day of averaging. The accuracy of GPS time link is reported to be better than 2 ns in long baseline link (10,000 km) in Asia-Pacific Zone.

Description: The idea that we highlight in this paper is how to reduce the computational complexity by limiting the processing in the receiver chain. For this we seek for limiting the use of the beamforming process and the equalization process according to the conditions. Indeed with the cognitive features the receiver observes its environment and decides to either keep or turn off these processes without degrading its performances. The decision method that we developed is based on the statistical modeling of the radio environment, the purpose of this approach is to minimize the percentage of bad decisions by considering the errors of observation. Furthermore we first address the two decision scenarios separately and we seek to prove that the decisions to turn off the equalizer and the beamforming, when they are not necessary, lead to reduce the computational complexity of the receiver. Then we focus on the behavior of the receiver facing both decision scenarios. Thus we formulate the decision problem intwo different ways, in the first case we consider that the receiver performs joint decisions about the two operations of beamforming and equalization, in the second case we suppose that it handles the two decision scenarios sequentially. We comparethen the performance of the receiver in the two cases.

Description: In this paper, a focusing reflectarray based on the conductor-backed strip dipole unit cell is proposed and designed for use in the microwave virus sanitizer. Unlike traditional far-field antennas that form a planar phase front in a specified far-field direction, the focusing reflectarray is designed to coherently add the fields radiated from the feeding antenna at a predetermined focal point, typically within its radiating near-field region, and to ensure adequate power density to inactivate the H3N2 virus sample. Furthermore, the focusing reflectarray has a simple and planar structure compared with conventional focusing antennas. Since the microwave resonant absorption frequency of the H3N2 virus is at about 8 GHz, an 8 × 8 focusing reflectarray is designed for operation at 8 GHz. A prototype antenna is then fabricated and used for H3N2 virus sanitization. It is demonstrated experimentally that the death rate of the H3N2 virus sample is up to 93%, verifying the feasibility of the microwave virus sanitizer as well as the proposed focusing reflectarray.

Description: This article analyzes the response of a sphere with radially anisotropic permittivity dyadic (RA sphere), in both the electrostatic and full electrodynamic settings. Depending on the values and signs of the permittivity components, the quasistatic polarizability of the RA sphere exhibits several very different interesting properties, including invisibility, field concentration, resonant singularities, and emergent losses. Special attention is given to the anomalous losses that appear in the case of certain hyperbolic anisotropy values. We show that their validity can be justified in a limiting sense by puncturing the sphere at the origin and adding a small imaginary part into the permittivity components. A hyperbolic RA sphere with very small intrinsic losses can thus have significant effective losses making it an effective absorber. With different choice of permittivities, the RA sphere could also perform as a cloak or a sensor. The Mie scattering results by an RA sphere are used to justify the quasistatic calculations. It is shown that in the small parameter limit the absorption efficiency of an RA sphere is non-zero for certain lossless hyperbolic anisotropies. The absorption and scattering efficiencies agree with the quasistatic calculations fairly well for spheres with size parameters up to 1/3.

Description: Same-beam Very Long Baseline Interferometry (VLBI) observations were performed between the rover and the lander of Chang'E-3 and differential phase delay data were obtained with the minimum random error of about 0.03 ps. These data were used to monitor the rover motions, as small as several centimeters, including movement, turning, and attitude adjustment. The relative position between the rover and the lander was precisely measured with an accuracy of 1 m, which is an improvement of ten times compared with that of the Apollo project.

Description: This investigation assesses the attenuation induced by snowfall on an experimental slant-path link that monitors the 20.199 GHz beacon signal of the Anik F2 satellite. Beacon data collected at CRC in Ottawa over two years, including the winters of 2010–2011 and 2011–2012, were analyzed as part of this study. The antenna of one of the two receivers used in the propagation campaign with Anik F2 was shielded, the first year under a tent and the second year under the roof of a building, in order to prevent degradations on the measured beacon signal due to snow or ice accumulation on the parabolic reflector surface. One of the main challenges of the study was the unambiguous identification of snow events. Information provided by several weather sensors, a profiling radiometer, and meteorological reports were used to help identify the type of precipitation. Events of wet and dry snow along with freezing rain are presented and discussed. Radiometric measurements of sky noise temperature were particularly useful to detect light snowfall events and to estimate event durations. Statistics of snow attenuation were derived for the winter months of the study. It is found that snow attenuation is modest at 20.2 GHz however, modest attenuation may be important for small-margin communication systems.

Description: Different heuristic approaches, such as physical optics method, method of equivalent edge currents and newly developed modified method of equivalent edge currents are exemplified in a problem of electromagnetic diffraction by a plane angular sector. Comparing with rigorous results has shown that for the problem of electromagnetic diffraction by polyhedrons physical optics method can lead to serious mistakes, method of equivalent edge currents gives a qualitatively correct solution and modified solution by equivalent edge currents method is the most close to a rigorous one. Results of this work can be extended to many scientific and engineering applications in various fields of physics and technology.

Description: The absolute field correlations in atmospheric turbulence are evaluated for the off-axis optical Gaussian beam incidence. Evaluations in the practical range of the source and the turbulent medium parameters show that an increase in the diagonal length at the receiver plane causes the absolute field correlations of the off-axis Gaussian beam to decrease. At a fixed receiver diagonal length, the off-axis Gaussian beams having smaller displacement parameters and larger source sizes exhibit larger absolute field correlations. Comparing the absolute field correlations of the off-axis Gaussian beams in atmospheric turbulence with their no turbulence counterparts, it is observed that the behaviour of the absolute field correlation variations remain the same, however the diminishing of the absolute field correlations in turbulence occurs at smaller diagonal lengths.

Description: No abstract is available for this article.

Description: A two-layer model of Mars’ regolith/bedrock media with a cratered rough surface/subsurface is presented for radar echo simulation of planetary exploration research. The numerical approach of geometric ray tracing for the scattering of rough surfaces, which is digitized by the triangulated network, is applied to the calculation of the scattering and imaging simulation of radar range echoes. Numerical simulations of a cratered rough surface generated by the Monte Carlo method are used to analyze the functional dependence of radar range echoes at 1–50 MHz center frequencies upon the surface/subsurface feature and the parameters of the layering media, that is, layer depth and dielectric properties. The radar range echoes from two areas of the real Mars surface, which is described by DEM (digital elevation model) data with a resolution of 1 m × 1 m and a vertical error of less than 1 m, are also simulated and analyzed. Based on these simulations, this study presents a numerical imaging test of radar sounder at center frequencies 1–50 MHz for exploration of different dielectric regolith and bedrock media. The channel 50 MHz with high resolution might be an optimal frequency. Finally, inversion of the dielectric constants of the two-layer media and the regolith layer thickness are developed.

Description: Propagation measurements have been carried out on a 43 kilometre long 13 GHz 128 QAM over-water path in the coastal regions of Norway. The measurements lasted for 18 months. The intention with the measurements on this in-service radio link was to compare results with models given by the Rec. ITU-R P. 530–15 [1]. The attenuation due to combined rain and wet snow was of special interest, since the radio link is situated in an area – Trondheimsfjorden – that has a significant amount of wet snow in winter. The radio link experienced outages due to multipath, rain and wet snow, where the latter were the predominant outage cause. The fading due to combined rain and wet snow resembled the shape of the model given in Rec. ITU-R P. 530–15 [1], but the model under-predicts the amount of fading. In addition to outages (performance degradation and unavailability) and fading, various other parameters such as fading speed, enhancement, average fade duration, and number of fade events; have been measured and compared to Rec. ITU-R P. 530–15 [1]. The radio link activity has also been compared to the weather conditions at the time for the most severe fading incidents.

Description: Numerical modelling has demonstrated that ADS-B signals can be used to reconstruct two dimensional (2D) electron density maps of the ionosphere using techniques for computerized tomography (CT). Ray-tracing techniques were used to determine the characteristics of individual waves, including the wave path and the state of polarization at the satellite receiver. The modelled Faraday rotation was computed and converted to total electron content (TEC) along the ray paths. The resulting TEC was used as input for computerized ionospheric tomography (CIT) using algebraic reconstruction technique (ART). This study concentrated on reconstructing meso-scale structures 25–100 km in horizontal extent. The primary scientific interest of this study was to show that ADS-B signals can be used as a new source of data for CIT to image the ionosphere and to obtain a better understanding of magneto-ionic wave propagation.

Description: The information from reflected Global Navigation Satellite System (GNSS) signals can become a valuable data source, from which geophysical properties can be deduced. This approach, called GNSS-Reflectometry (GNSS-R), can be used to develop instruments that act like an altimeter when arrival times of direct and reflected signals are compared. Current GNSS-R systems usually entirely rely on signals from the Global Positioning Service (GPS), and field experiments could demonstrate that information from such systems can measure sea level with an accuracy of a few centimeter. However, the usage of the Russian GLONASS system has the potential to simplify the processing scheme and to allow handling of direct and reflected signals like a bi-static radar. Thus, such a system has been developed and deployed for test purposes at the Onsala Space Observatory, Sweden, that has an operational GPS-based GNSS-R system. Over a period of two weeks in October 2013, GPS-based GNSS-R sea-level monitoring and measurements with the newly developed GLONASS-R system were carried out in parallel. In addition, data from co-located tide gauge measurements were available for comparison. It can be shown that precision and accuracy of the GLONASS-based GNSS-R system is comparable to, or even better than, conventional GPS-based GNSS-R solutions. Moreover, the simplicity of the newly developed GLONASS-R system allows to make it a cheap and valuable tool for various remote sensing applications.

Description: The Modified Edge Representation (MER) is a procedure for defining the equivalent edge currents (EECs) to be used in the surface-to-line integral reduction for computing the Physical Optics radiation integrals in diffraction analysis. The Physical Optics surface integration is transformed into the line integration of MER-EECs rigorously for the planar surfaces. It works with the remarkable accuracy even for the curved surface. In contrast to conventional EECs, those in MER are defined without ambiguity not only at the diffraction points but also at arbitrary ones along the periphery. One remarkable advantage is that the MER-EECs, after integrated along periphery, provide uniform fields across the geometrical shadow boundaries though the EECs in the integrand consist of non-uniform Keller-type diffraction coefficients. As the starting point of the applicability check of MER for the curved surfaces, this paper investigates the MER diffraction field behaviors on and near the reflection shadow boundary (RSB). Firstly, the stabilities or the robustness of the numerical line integration are interpreted. Secondly, the dependence of the RSB field errors upon the curvature of the surfaces is investigated. They become smaller in higher frequency and are related with the aberration of the geometrical reflected ray; for the dipole wave illumination, the error is generally smaller and larger for the concave and convex surfaces, respectively. This surface shape dependence of MER errors in diffraction is quite analogous to those in predicting GO contributions, the latter of which is the complement of the former and were previously reported by the authors.

Description: This paper presents two digital transmission techniques for long haul ionospheric links. Since 2003 we have studied the HF link between the Antarctic Spanish Base, Juan Carlos I, and Spain and we have described the link in terms of availability, signal to noise ratio (SNR) and delay and Doppler power profile. Based on these previous studies we have developed a test bed to investigate two digital transmission techniques, i.e. Direct Sequence Spread Spectrum and Orthogonal Frequency Division Multiplexing, which can provide a low power, low rate ionospheric data link from Antarctica. Symbol length, bandwidth and constellation are some of the features that are analyzed in this work. Data gathered from the link throughout the 2010/2011 and 2011/2012 Antarctic surveys show that spread spectrum techniques can be used to transmit data at low rate when the channel forecast is poor but when the channel forecast is good multicarrier techniques can be used to transmit sporadic bursts of data at higher rate.

Description: The CERTO radio beacon on the C/NOFS satellite sends VHF/UHF radio signals at 150 and 400 MHz to provide measurements of integrated electron density or Total Electron Content (TEC) by an east-west chain of ground receivers in Peru. Computerized Ionospheric Tomography (CIT) is used to convert the TEC data into two dimensional images of electron densities with maximum 5 × 5 km resolution in Longitude-Altitude space. These images are updated every 95 minutes as the C/NOFS satellite passes over the receiver network in its low-latitude orbit with an inclination of 12 Degrees. The 2-D, high resolution images of the ionosphere are used to predict the impact of equatorial plasma structures on HF propagation of radar and radio signals. Electron density measurements from the NRL radio tomography chain across Peru are used for simulations of the performance by HF one-way links. HF rays from transmitter to receiver are traced through the electron density images produced by radio beacon tomography. Eight separate paths are found between a transmitter and ground receiver separated by 2000 km. A total of 36 backscatter echoes are found with unique group delay, Doppler frequency shift, phase delay, and echo amplitude. This multi-path effect explains the range and Doppler spreading of observations for HF monostatic radar propagation through F-Layer irregularities. This type of analysis is useful for prediction and interpretation of range and Doppler observations from HF systems including over-the-horizon and SuperDARN radars, HF Geolocation Arrays, and HF communications networks.

Description: No abstract is available for this article.

Description: [1]  This paper describes a field campaign performed with a ground-based polarimetric tomographic imager designed to measure the vertical response of several forest plots in order to better understand the mechanisms contributing to the total radar response. The campaign took place in the Mende forest, an artificial forest of European Black Pines, in the South of France. The objective is to perform a sensitivity study on the radar observables based on biophysical parameters. This paper presents a description of the experiment hardware and procedure, the results obtained for all sites, and a discussion of the results in the light of the ground truth. The results show the vertical distribution of the backscattered intensity for several parameters like tree density, forest growth, presence of undergrowth and ground slope. The evolution of the energy backscattered by the ground, the volume, and the whole forest structure is also displayed. These results have shown the interest of such a campaign to improve the understanding of the distribution of radar mechanisms along the vertical axis.

Description: [1]  Future wireless communication systems will most likely be operated at carrier frequencies above 300 GHz, where the indoor radio channel behaves entirely differently compared to legacy radio communication frequencies. Being highly relevant for system performance evaluations and channel modeling, the spatial as well as the temporal dispersions are studied for a representative office wireless LAN scenario in this paper. Ray tracing serves as the means for the accurate simulation of the THz radio wave propagation. Simple stochastic models are derived to approximate and reproduce the distance-dependent behavior of the angular spread as well as of the RMS delay spread. Based on the results, the maximum symbol rates achievable without any intersymbol interference are quantified and can be shown to reach up to several 100 GSymbols/s provided that highly directive antennas are used.

Description: ABSTRACT On February 15, 2013, the Chelyabinsk meteor event (the largest in size since 1908) provided a unique opportunity to observe ionospheric perturbations associated with the ablation and ionospheric impact of the meteor using GPS measurements. The hypersonic bolide generated powerful shock waves while acoustic perturbations in the atmosphere led to the upward propagation of acoustic and gravity waves into the ionosphere. In our research, we applied two different techniques to detect ionospheric disturbances in dual-frequency global positioning system (GPS) measurements during the meteor impact event. The data were collected from near-field GPS networks in Russia, GEONET in Japan, and Plate Boundary Observatory (PBO) stations in the coterminous U.S. Using a novel wavelet coherence detection technique, we were able to identify three different wave trains in the measurements collected from the nearest GPS station to the meteor impact site, with frequencies of approximately 4.0 - 7.8 mHz, 1.0 - 2.5 mHz, and 2.7 – 11 mHz at 03:30 UTC. We estimated the speed and direction of arrival of the total electron content (TEC) disturbances by cross-correlating TEC time series for every pair of stations in several areas of the GEONET and PBO networks. The results may be characterized as three different types of traveling ionospheric disturbances (TIDs). First, the higher frequency (4.0 - 7.8 mHz) disturbances were observed around the station ARTU in Arti, Russia (56.43° N, 58.56° E), with an estimated mean propagation speed of about 862 ± 65 m/s (with 95% confidence interval). Another type of TID disturbance related to the wave trains was identified in the lower frequency band (1.0 - 2.5 mHz), propagating with a mean speed of 362 ± 23 m/s. The lower frequency ionospheric perturbations were observed at distances of 300-1500 km away from Chelyabinsk. The third type of TID wave train was identified using the PBO stations in the relative short period range of 1.5 - 6 minutes (2.7 – 11 mHz) with a mean propagation speed of 733 ± 36 m/s. The observed short-period ionospheric perturbations in the U.S. region is, to the best of our knowledge, the first observational evidence of the coincident the long-range meteor-generated infrasound signals propagating in the ionosphere.

Description: Ionospheric scintillation is a phenomenon that occurs after sunset, especially in the low-latitude region, affecting radio signals that propagate through the ionosphere. Depending on geophysical conditions, ionospheric scintillation may cause availability and precision problems to Global Navigation Satellite Systems (GNSS) users. The present work is concerned with the development of an extended model for describing the effects of the amplitude ionospheric scintillation on GPS receivers. Using the α-μ probabilistic model, introduced by previous authors in different contexts, the variance of GPS receiver tracking loops error may be estimated more realistically. The proposed model is developed with basis on the α-μ parameters and also considering correlation between amplitude and phase scintillation. Its results are interpreted to explain how a receiver may experience different error values under the influence of ionospheric conditions leading to a fixed scintillation level S 4 . The model is applied to a large experimental data set obtained at São José dos Campos, Brazil, near the peak of the Equatorial Anomaly during high solar flux conditions, between December 2001 and January 2002. The results from the proposed model show that, depending on the α-μ pair, moderate scintillation (0.5 ≤ S 4  ≤ 0.7) may be an issue for the receiver performance. When S 4  〉 0.7, the results indicate that the effects of scintillation are serious, leading to a reduction in the receiver availability for providing positioning solutions in approximately 50% of the cases.

Description: New perfect frequency selective surface (FSS) metamaterial absorbers (MAs) based on resonator with dielectric configuration are numerically presented and investigated for both microwave and terahertz frequency ranges. Also, to verify the behaviors of the FSS MAs, one of the MAs is experimentally analyzed and tested in the microwave frequency range. Suggested FSS MAs have simple configuration which introduces flexibility to adjust their FSS metamaterial (MTM) properties and to re-scale the structure easily for any desired frequency range. There is no study which simultaneously includes microwave and terahertz absorbers in a single design in the literature. Besides, numerical simulations verify that the FSS MAs could achieve very high absorption levels at wide angles of incidence for both transverse electric ( TE ) and transverse magnetic ( TM ) waves. The proposed FSS MAs and their variations enable many potential application areas in radar systems, communication, stealth technologies, and so on.

Description: No abstract is available for this article.

Description: ABSTRACT The launch of the SMOS mission 2-Nov-2009 marked a milestone in remote sensing for it was the first time a radiometer capable of acquiring wide field of view images at every single snapshot, a unique feature of the synthetic aperture technique, made it to space. The technology behind such an achievement was developed thanks to the effort of a community of researchers and engineers in different groups around the world. It was only because of their joint work that SMOS finally became a reality. The fact that the European Space Agency, together with CNES (Centre National d'Etudes Spatiales) and CDTI (Centro para el Desarrollo Tecnológico e Industrial), managed to get the project through should be considered a merit and a reward for that entire community. This paper is an invited historical review that, within a very limited number of pages, tries to provide insight into some of the developments which, one way or another, are imprinted in the name of SMOS.

Description: Pronounced amplitude minima are observed during the sub-ionospheric propagation of VLF waves at times (Terminator Times or TTs) when the Terminator Line crosses given locations along the propagation path. The distance between such two successive locations is called the modal interference distance D, which is related to nighttime mode propagation in the Earth-Ionosphere waveguide. Therefore, the temporal behavior of the distance D can bring information on the dynamics of the nighttime lower ionosphere and on the presence of external forcing agents, including those associated with seismic activity. In this paper we present a methodology to estimate the modal interference distance D based on the measure and analysis of the pronounced VLF amplitude minima. We have used a long-term database of almost 5 years from three different VLF propagation paths from the South America VLF Network (SAVNET). We emphasize that the accuracy of the determination of the distance D achieved by our method is better than those obtained in earlier studies. The reason for that is the use of a long-term continuous database, from different parallel propagation paths mainly oriented along the east-to-west direction. We discuss typical properties of the obtained distance D, as the simultaneous occurrence of amplitude minima for parallel propagation paths, anomalous values of D at locations where the Terminator line is close to the receiver, and the derivation of the undisturbed nighttime ionospheric height at h N ~88 km.

Description: High frequency heating of the ionosphere is effective for generating extremely low frequencies (ELF, 3–3000 Hz) through modulation of the auroral electrojet current. While the amplitudes of the resulting ELF waves depend on the auroral electrojet currentstrength, the polarization of their horizontal magnetic field remains relatively stable. In this work, we determined that at the distance of several wavelengths from an ionospheric ELF source created by two HF heating waves separated by an ELF frequency, polarization parameters are influenced by the Earth-ionosphere waveguide. Previous experiments in the vicinity of the ionospheric ELF source have determined that the right-hand polarization of the magnetic field measured at the ground typically prevails, whereas in this paper we demonstrate that at the distance of 660 km to the east of the EISCAT a circular left-hand polarization dominates. We interpret this effect as a result of " trapping" of the left-hand mode between the upper and lower boundaries of the Earth-ionosphere waveguide, while the right-hand or whistler mode leaks into the ionosphere.

Description: Joint observations of the Rankin Inlet (RKN) and Inuvik (INV) Super Dual Auroral Radra Network (SuperDARN) HF radars and Resolute Bay (RB) Canadian Advanced Digital Ionosonde (CADI) are used to assess the electron density at the F region peak and the electric field magnitude as factors affecting echo detection over RB. We demonstrate that the radars show similar diurnal and seasonal variations in ionospheric echo occurrence. During nightime and at radar frequencies of ~12 MHz, optimum densities for both radars are shown to be ∼ 1.4 × 10 5   cm − 3 , ~1.8 × 10 5   cm − 3 and ~2.0 × 10 5   cm − 3 for winter, equinox and summer, respectively. During daytime, optimum densities are larger by (0.2 − 0.3) × 10 5   cm − 3 . Observations at lower radar frequencies of ~10 MHz show smaller required densities during nightime, by ~0.3 × 10 5   cm − 3 . Optimum electric fields for the moments of echo detection over RB are found to be 5-25 mV/m with no clear threshold effect and any seasonal dependence. The presented data suggest that for echo detection favourable propagation conditions along the entire path of radio waves toward the scattering volume are important.

Description: No abstract is available for this article.

Description: This paper attempts to tackle one of the challenges faced in soft input soft output Multiple Input Multiple Output (MIMO) detection systems, which is to achieve optimal error rate performance with minimal power consumption. This is realized by proposing a new algorithm design that comprises multiple thresholds within the detector that, in real time, specify the receiver behavior according to the current channel in both slow and fast fading conditions, giving it adaptivity. This adaptivity enables energy savings within the system since the receiver chooses whether to accept or to reject the transmission, according to the success rate of detecting thresholds. The thresholds are calculated using the mutual information of the instantaneous channel conditions between the transmitting and receiving antennas of iterative-MIMO systems. In addition, the power saving technique, Dynamic Voltage and Frequency Scaling, helps to reduce the circuit power demands of the adaptive algorithm. This adaptivity has the potential to save up to 30% of the total energy when it is implemented on Xilinx®Virtex-5 simulation hardware. Results indicate the benefits of having this ‘intelligence’ in the adaptive algorithm due to the promising performance-complexity trade-off parameters in both software and hardware co-design simulation.

Description: As both the bit rate required by applications on mobile devices and the number of those mobile devices are steadily growing, wireless access networks need to be expanded. As wireless networks also consume a lot of energy, it is important to develop energy-efficient wireless access networks in the near future. In this study, a capacity-based deployment tool for the design of energy-efficient wireless access networks is proposed. Capacity-based means that the network responds to the instantaneous bit rate requirements of the users active in the selected area. To the best of our knowledge, such a deployment tool for energy-efficient wireless access networks has never been presented before. This deployment tool is applied to a realistic case in Ghent, Belgium to investigate three main functionalities incorporated in LTE-Advanced: carrier aggregation, heterogeneous deployments, and Multiple-Input Multiple-Output (MIMO). The results show that it is recommended to introduce femtocell base stations, supporting both MIMO and carrier aggregation, into the network (heterogeneous deployment) to reduce the network's power consumption. For the selected area and the assumptions made, this results in a power consumption reduction up to 70%. Introducing femtocell BSs without MIMO and carrier aggregation can already result in a significant power consumption reduction of 38%.

Description: No abstract is available for this article.

Description: No abstract is available for this article.

Description: Studies of rain drop shapes, oscillation modes, and implications for radiowave propagation are presented. Drop shape measurements in natural rain using 2D video disdrometers (2DVDs) are discussed. As a representative exception to vast majority of the cases where the “most probable” shapes conform to the axisymmetric (2,0) oscillation mode, an event with a highly organized line convection embedded within a larger rain system is studied. Measurements using two collocated 2DVD instruments and a C-band polarimetric radar clearly show the occurrence of mixed-mode drop oscillations within the line, which in turn is attributed to sustained drop collisions. Moreover, the fraction of asymmetric drops determined from the 2DVD camera data increases with the calculated collision probability when examined as time series. Recent wind-tunnel experiments of drop collisions are also discussed. They show mixed-mode oscillations, with (2,1) and (2,2) modes dramatically increasing in oscillation amplitudes, in addition to the (2,0) mode, immediately upon collision. The damping time constant of the perturbation caused by the collision is comparable to the inverse of the collision frequency within the line convection. Scattering calculations using an advanced method-of-moments numerical technique are performed to accurately and efficiently determine the pertinent parameters of electrically large oscillating rain drops with asymmetric shapes needed for radiowave propagation. The simulations show that the scattering matrix and differential reflectivity of drops are dependent on the particular oscillation modes and different time instants within the oscillation cycle. The technique can be utilized in conjunction with 3D reconstruction of drop shapes from 2DVD data.

Description: GPS radio occultation (RO) signals are sometimes observed very deep in the Earth's shadow. To investigate these phenomena, one of the FORMOSAT-3/COSMIC RO receivers was set to track RO signals deep below the limb, down to a height of straight line -350 km on October 5-6, 2010. Analysis of the spectrograms revealed the existence of two types of signals below -200 km, RO signals induced by tropospheric propagation and interfering signals not transmitted by the occulted GPS. The RO signals induced by tropospheric propagation arrive from impact heights corresponding to inversion layers. Wave optics modeling of RO signals showed that deep signals exist when the refractivity gradient exceeds critical (super-refraction). The existence of such signals is a diffractional phenomenon, which offers a new quality control parameter to identify occultations that may be affected by super-refraction. This is important for RO data assimilation in weather models in the moist lower troposphere because assimilation of RO data affected by super-refraction is an ill-conditioned problem. Detection of the tropospheric ducts also may be useful for evaluation of radio wave propagation conditions. For infinitely horizontally extended ducts, the deep signals are extended in duration, have amplitudes of about 0.1% and exist for only elevated ducts. For ducts of limited horizontal extension, the deep signals are shorter in duration, have amplitude of about 1% and may exist for both elevated and surface ducts. The interfering signals were found in about half of occultations. Based on frequency modeling, in most cases, the interfering signal were identified with non-occulted GPS. The disturbance of retrieved bending angle induced by an interfering signal from a non-occulted GPS in a region of strong defocusing and significant spectral spread of RO signal was modeled and determined to be quite large, up to 10% of bending angle. However, the probability of occurrence of such interference (not estimated), generally, must be low. Removal of the interfering signal by high-pass filtering was tested but it introduced a disturbance of bending angle of about the same magnitude as the interfering signal itself.

Description: The impulsive electromagnetic response of a thin metallic coating on a dielectric half-space is analytically investigated. Both TM - and TE -polarized electromagnetic fields in the configuration are excited by an impulsive line source. The problem is analytically solved with the help of the high-contrast thin-sheet boundary conditions and the extended Cagniard-DeHoop technique. Closed-form space-time expressions for electromagnetic fields are found, numerically evaluated and discussed with regard to the pulsed excitation of surface plasmon phenomena.

Description: No abstract is available for this article.

Description: In this paper we provide a review of the vehicle-to-vehicle (V2V) wireless propagation channel. This “car-to-car” application will be used to improve roadway efficiency, provide unique traveler services, and can also enable safety applications that can save lives. We briefly review some currently envisioned applications and the initial V2V radio technology, then address the V2V propagation channel. Propagation basics germane to the V2V setting are described, followed by a discussion of channel dispersion and time variation. The channel impulse response and its Fourier transform, the channel transfer function, are described in detail, and their common statistical characterizations are also reviewed. The most common models for the V2V channel—the tapped-delay line and geometry-based stochastic channel models—are covered in some detail. We highlight key differences between the V2V channel and the well-known cellular radio channel. These differences are more rapid time variation and higher probability of obstruction of the direct line of sight component; modeling of these effects has required some novel approaches. The V2V channel's non-stationary statistical behavior is addressed, as is the use of multiple antenna systems. Remaining areas for future work are also described.

Description: We statistically analyzed lightning whistlers detected from the analog waveform data below 15 kHz observed by the VLF instruments onboard AKEBONO. We examined the large amount of data obtained at Uchinoura Space Center in Japan for 22 years from 1989 to 2010. The lightning whistlers were mainly observed inside the L -shell region below 2. Seasonal dependence of the occurrence frequency of lightning whistlers has two peaks around July to August and December to January. As lightning is most active in summer in general, these two peaks correspond to summer in the northern and southern hemispheres, respectively. Diurnal variation of the occurrence frequency showed that lightning whistlers begin to increase in the early evening and remain at a high occurrence level through the night with a peak around 21 in MLT. This peak shifts toward night side compared with lightning activity, which begins to rise around noon and peaks in the late afternoon. This trend is supposed to be caused by attenuation of VLF wave in the ionosphere in the daytime. Comparison study with the ground-based observation revealed consistent results, except that the peak of the ground-based observation appeared after midnight while our measurements obtained by AKEBONO was around 21 in MLT. This difference is explained qualitatively in terms of that lightning whistlers measured at the ground station passed through the ionosphere twice above both source region and the ground station. These facts provide an important clue to evaluate quantitatively the absorption effect of lightning whistler in the ionosphere.

Description: Aquarius is a combination active/passive instrument at L-band designed to map sea surface salinity globally from space. The radiometer (passive) is the primary instrument for retrieving salinity and the scatterometer (active) provides information to correct for a major source of error, sea surface roughness (waves). In addition, the radiometer includes a number of special features designed to meet the goal for this challenging measurement, including measurement of the third Stokes parameter to help with the correction for Faraday rotation and rapid sampling to help with the mitigation of radio frequency interference (RFI). Aquarius was launched on 10 June 2011 aboard the Aquarius/SAC-D observatory and has been working well. The salinity retrieval continues to improve and the special features suggest the potential for new applications of remote sensing from space at L-band.

Description: The integral equations of electromagnetic scattering are often solved numerically by means of the method of moments. At high frequencies, this method typically leads to a large linear system with a dense matrix. Higher order basis functions is a means to improve the accuracy. B-splines are used here for a two-dimensional testbed study that avoids the complexity of 3D implementation. For smooth convex scatterers one may use a priori knowledge about the oscillatory behaviour of the solution to reformulate the integral equation. This fast scale of variation is included in the kernel of the integral equation. An extension of this idea deals with the variation in the shadow, particularly for circular geometry, and is an improvement that is presented in this study. Generally, the TE-case is less studied at high frequencies and our numerical results therefore relate to this harder problem. A sparse matrix can be obtained by modification of the integration path in the integral equation. The decay of the modified kernel makes this possible for high frequencies but the modified path reduces the accuracy in the deep shadow. This study investigates these modified paths for the case where the shadow region is not omitted from the formulation.

Description: This paper describes the construction and use of ‘modified Taylor diagrams’ and the comparison of three real-time assimilative ionospheric models. The paper expands on the work by McNamara et al. [2013] and serves as an addendum to that work. Modified Taylor diagrams provide an easy way of visualizing and comparing statistical information about a number of models, and for multiple parameters, simultaneously. Using modified Taylor diagrams has led to new conclusions about the models tested in McNamara et al. [2013]; also the comparison of the data ingestion version of NeQuick is included. It is shown that the modified NeQuick model performs comparably with the data assimilation models from McNamara et al. [2013] and in multiple cases also shows considerable improvement, such as in hmF2 at the Hermanus Digisonde station.

Description: This paper applies new wavelet-based analysis procedures to low-earth-orbiting satellite measurements of equatorial ionospheric structure. The analysis was applied to high-resolution data from 285 C/NOFS satellite orbits sampling the post-sunset period at geomagnetic equatorial latitudes. The data were acquired during a period of progressively intensifying equatorial structure. The sampled altitude range varied from 400 to 800 km. The varying scan velocity remained within 20 degrees of the cross-field direction. Time-to-space interpolation generated uniform samples at approximately 8 m. A maximum segmentation length that supports stochastic structure characterization was identified. A two-component inverse-power-law model was fit to scale spectra derived from each segment together with a goodness-of-fit measure. Inverse-power-law parameters derived from the scale spectra were used to classify the scale spectra by type. The largest category was characterized by a single inverse power law with a mean spectral index somewhat larger than 2. No systematic departure from the inverse power law was observed to scales greater than 100 km. A small subset of the most highly disturbed passes at the lowest sampled altitudes could be categorized by two-component power-law spectra with a range of break scales from less than 100 m to several km. The results are discussed within the context of other analyses of in-situ data and spectral characteristics used for scintillation analyses.

Description: ABSTRACT Attenuation due to precipitation remains an important design factor in the future deployment of terrestrial and earth-space communication radio links. Largely, there are concerted efforts to understand the dynamics of precipitation in attenuation occurrence at subtropical, tropical and equatorial region of Africa. In this deliberate approach, rainfall spikes pertaining to rain cells are conceptualized as distinct rain spike traffic over radio links, by applying queueing theory concepts. The queue distributions at Durban (29°52′S, 30°58′E) and Butare (2°36′S, 29°44′E) – respectively of subtropical and equatorial climates – are investigated from distrometer measurements. The datasets at both sites are observed over four rain regimes: drizzle, widespread, shower and thunderstorm. The queue parameters of service time and inter-arrival of rain spikes traffic at both regions are found to be Erlang- k distributed ( E k ) and exponentially distributed (M) respectively. It is established that the appearance of rain rates over radio links invariably follows a First Come, First Served (FCFS), multi-server ( s ), infinite queue and semi-Markovian process, designated as M/ E k /s/∞/FCFS discipline. Modeled queue parameters at both regions are found to vary significantly over different regimes. However, these queue parameters over the entire dataset suggest similar queue patterns at both sites. More importantly, power-law relationships describing other queue-related parameters are formulated. The paper concludes by demonstrating an application of queueing theory for rainfall synthesis. The proposed technique will provide an alternative method of estimating rain cell sizes and rain attenuation over satellite and terrestrial links.

Description: In direction finding and localization applications, multipath signals are important sources of error for parameter estimation. When the antenna array receives multipath reflections which are coherent with the far-field line-of-sight signal, estimating the far- and near field components becomes an important problem. In this paper, a new method is proposed to estimate the direction-of-arrival (DOA) of the far-field source and to localize its near-field multipaths. Far-field source DOA is estimated using calibration of the antenna array. A near-to-far transformation is proposed for the estimation of the near-field source DOA angles. In order to estimate the near-field range parameters, a compressive sensing approach is presented where a dictionary with near-field sources with different ranges is employed. As a result, the proposed method estimates the far-field and near-field source DOAs as well as the range and the signal amplitudes of the near-field sources. This method is evaluated using close-to-real world data generated by a numerical electromagnetic tool, where the array and transmitter are placed in an irregular terrain and array data is generated using Full 3-D propagation model. It is shown that unknown source parameters can be estimated effectively showing the potential of the proposed approach in applications involving High Frequency (HF) direction finding and indoor localization.

Description: The neutral winds in the mesosphere and lower thermosphere (MLT) region are measured by a newly installed meteor trail detection system (or meteor radar) at Chung-Li, Taiwan, for the period 10 - 25 November 2012 which includes the Leonid meteor shower period. In this study, we use the 3-m field-aligned plasma irregularities in the sporadic E (Es) region in combination with the International Geomagnetic Reference Field (IGRF) model to calibrate the system phase biases such that the true positions of the meteor trails can be correctly determined with interferometry technique. The horizontal wind velocities estimated from the radial velocities of the meteor trails and their locations by using a least-squares method show that the diurnal tide dominates the variation of the MLT neutral wind with time over Chung-Li, which is in good agreement with the HWM07 model prediction. However, harmonic analysis reveals that the amplitudes of the mean wind, diurnal and semi-diurnal tides of the radar-measured winds in height range 82-100 km are systematically larger than those of the model-predicted winds by up to a factor of 3. A comparison shows that the overall pattern of the height-local time distribution of the composite radar-measured meteor wind is in general consistent with that of the TIDI-observed wind, which is dominated by a diurnal oscillation with downward phase progression at a rate of about 1.3 km/hr. The occurrences of the Es layers retrieved from fluctuations of the amplitude and excess phase of the GPS signal received by the FORMOSAT-3/COSMIC satellites during the GPS radio occultation (RO) process are compared with the shear zones of the radar-measured meteor wind and HWM07 model wind. The result shows that almost all of the RO-retrieved Es layers occur within the wind shear zones that favor the Es layer formation based on the wind shear theory, suggesting that the primary physical process responsible for the Es layer events retrieved from the scintillations of the GPS RO signal is very likely the plasma convergence effect of the neutral wind shear.

Description: Using a multiple-scale homogenization method, we derive generalized sheet transition conditions (GSTCs) for an arbitrarily shaped coated-wire grating. The parameters in these GSTCs are interpreted as effective electric and magnetic surface susceptibilities and surface porosities of the wire grating. We give expressions for determining these surface parameters for any arbitrarily shaped grating. We show that these GSTCs are a generalized form of the boundary conditions derived earlier by Wainstein and Sivov, who analyzed the case of symmetric, uncoated wire gratings. This work is also a first step in developing GSTCs for more general types of structures such as metasurfaces, metafilms and metascreens.

Description: A 12-m diameter radio telescope will be deployed to the Summit Station in Greenland to provide direct confirmation of a Super Massive Black Hole (SMBH) by observing its shadow image in the active galaxy M87. The telescope (Greenland Telescope: GLT) is to become one of the Very Long Baseline Interferometry (VLBI) stations at sub-millimeter (submm) regime, providing the longest baseline 〉 9,000 km to achieve an exceptional angular resolution of 20 µas at 350 GHz, which will enable us to resolve the shadow size of ~40 µas. The triangle with the longest baselines formed by the GLT, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and the Submillimeter Array (SMA) in Hawaii will play a key role for the M87 observations. We have been working on the image simulations based on realistic conditions for a better understanding of the possible observed images. In parallel, retrofitting of the telescope and the site developments are in progress. Based on three years of opacity monitoring at 225 GHz, our measurements indicate that the site is excellent for submm observations, comparable to the ALMA site. The GLT is also expected to make single-dish observations up to 1.5 THz.

Description: The study of long-term changes requires researchers to identify relevant historical measurements; quantifying and quality-controlling these measurements becomes central to their utilization by broader communities. This pilot study reports on the evaluation of ionograms and their inversion from the decade prior to the Space Age. The ionograms were recorded on 35 mm film reels and archived at the National Geophysical Data Center (NGDC) World Data Center A in Boulder, Colorado. For this study, ionogram film from one of the earliest operational sites in North America, Fort Belvoir (near Washington D.C.) is analyzed. This analysis generates two distinct products: a digital ionogram with virtual height and frequency coordinate registration, and scaled values including an electron density profile (EDP). Validation of the ionogram registration and its resolution are described. The scaling and inversion processing, including uncertainties for the parameters and quality assessment, are explained. This study demonstrates how the archived film ionograms can have extensive value as historic measurements of the ionosphere once they are digitized and coordinate-registered. Furthermore, modern analysis of the ionograms shows that a complete bottomside ionospheric specification may be obtained at better time resolution than is typically available from original scaled data. This research has set the stage for an effective recovery of ionospheric information for almost a full solar cycle prior to IGY. In addition, between Fort Belvoir and Wallops Island archives, an East Coast mid-latitude ionospheric data set can be generated from the late 1940s through the present.

Description: The human body is an extremely challenging environment for the operation of wireless communications systems, not least because of the complex antenna-body electromagnetic interaction effects which can occur. This is further compounded by the impact of movement and the propagation characteristics of the local environment which all have an effect upon body centric communications channels. As the successful design of body area networks (BANs) and other types of body centric system is inextricably linked to a thorough understanding of these factors, the aim of this paper is to conduct a survey of the current state-of-the-art in relation to propagation and channel models primarily for BANs but also considering other types of body centric communications. We initially discuss some of the standardization efforts performed by the IEEE 802.15.6 task group before focusing on the two most popular types of technologies currently being considered for BANs, namely narrowband and Ultra-wideband (UWB) communications. For narrowband communications the applicability of a generic path loss model is contended, before presenting some of the scenario specific models which have proven successful. The impacts of human body shadowing and small-scale fading are also presented alongside some of the most recent research into the Doppler and time dependencies of BANs. For UWB BAN communications, we again consider the path loss as well as empirical tap-delay line models developed from a number of extensive channel measurement campaigns conducted by research institutions around the world. Ongoing efforts within collaborative projects such as COST Action IC1004 are also described. Finally, recent years have also seen significant developments in other areas of body centric communications such as off-body and body-to-body communications. We highlight some of the newest relevant research in these areas as well as discussing some of the advanced topics which are currently being addressed in the field of body-centric communications.

Description: The solution of the time-harmonic Maxwell equations using a boundary element method, for 2-D geometries illuminated by arbitrary 3-D excitations, gives rise to numerical difficulties if highly conductive media are present. In particular, the interactionintegrals arising in the method of moments involve kernels that strongly oscillate in space and, at the same time, decay exponentially. We present an accurate method to tackle these issues over a very broad conductivity range (from lossy dielectric to conductor skin-effect regime), for both magnetic and non-magnetic conductors. Important applications are the modal analysis of waveguides with non-perfect conductors, scattering problems and shielding problems with enclosures with arbitrary permeability and conductivity and 3-D noise sources.

Description: No abstract is available for this article.

Description: In this paper, we developed best-fit values for parameters in the Cole–Cole model for the dielectric properties of 43 biological tissues and organs. We developed a parameter-fitting algorithm to build an empirical dataset for frequencies between 1 MHz and 20 GHz. Using the dielectric properties obtained from the fitted Cole–Cole parameters, we conducted numerical dosimetry, assessed energy absorption inside a human body exposed to electromagnetic radiation and compared the results with those obtained on a de facto database.

Description: We present the Hylaty geophysical station, a high sensitivity and low noise facility for Extremely Low Frequency (ELF, 0.03 – 300 Hz) electromagnetic field measurements, which enables a variety of geophysical and climatological research related to atmospheric, ionospheric, magnetospheric and space weather physics. The first systematic observations of ELF electromagnetic fields at the Jagiellonian University were undertaken in 1994. At the beginning the measurements were carried out sporadically, during expeditions to sparsely populated areas of the Bieszczady Mountains in the south-east of Poland. In 2004, an automatic Hylaty ELF Station was built there – in a very low electromagnetic noise environment, which enabled continuous recording of the magnetic field components of the ELF electromagnetic field in the frequency range below 60 Hz. In 2013, after 8 years of successful operation, the station was upgraded by extending its frequency range up to 300 Hz. In this paper we show the station's technical setup, and how it has changed over the years. We discuss the design of ELF equipment, including antennas, receivers, the time control circuit, and power supply, as well as antenna and receiver calibration. We also discuss the methodology we developed for observations of the Schumann resonance and wideband observations of ELF field pulses. We provide examples of various kinds of signals recorded at the station.

Description: This paper presents the design of an antenna array utilizing stacked multi-loop structures to produce the electromagnetic radiations with dual-circular polarizations and multiple directional beams. In particular, with a proper design of isolations, each combination of these polarizations and beams can be operated in a relatively independent fashion to increase the system capacity by using a single antenna set. The antenna structure was validated by numerical simulations and experimental measurements, which are presented to exhibit the characteristics of radiation.