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  • Other Sources  (252)
  • COMMUNICATIONS AND RADAR  (252)
  • 1980-1984  (252)
  • 1950-1954
  • 1925-1929
  • 1983  (252)
  • 1
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    Atmospheric attenuation for correlated satellite communication ground sites (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Link margin estimates are calculated for 30/20 GHz satellite communication systems employing closely-spaced (4 to 100 km) 'dual diversity' switched ground sites. The link margin estimates are based on a new analysis in which the bivariate rain attenuation density function for two correlated ground sites is modelled by an exponential density function. The results of the exponential density function analysis enable derivation of a direct relation between rain margin estimates and probability of exceedance (link availability). Margins typically in the range 2 to 12 dB are calculated for various ground site separations and summarized for seven city locations and five satellite orbit positions over the U.S. The results can be easily extended to other EHF satellite frequencies and other locations.
    Keywords: COMMUNICATIONS AND RADAR
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  • 2
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    Effects of ISI and satellite channel nonlinearity on Viterbi demodulation/decoding (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: It is shown that, for convolutionally coded transmission over bandwidth-constrained channels, a mere reversal of the switching direction at the encoder output produces a change in the system bit error probability performance. This change is significant when the Viterbi demodulator/decoder is matched to the total channel memory and is more significant for linear channels than for nonlinear ones. The reversal of switching direction is a simple demonstration of the fact that the well-known optimum codes for the linear AGWN channel are no longer necessarily optimum for a bandwidth-constrained channel with or without the addition of channel nonlinearity. It is concluded that potentially significant performance improvement can be obtained by matching the encoder (through the appropriate choice of tap weights and modulo-2 summers) to the channel in addition to matching the demodulator/decoder to the channel for a given encoder.
    Keywords: COMMUNICATIONS AND RADAR
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  • 3
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    Differential versus limiter-discriminator detection of narrow-band FM (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The error probability performance of differential detection of narrow-band FM is determined and compared with the analogous results for limiter-discriminator detection of the same modulation. It is shown that over a large class of benign and hostile environments, e.g., Gaussian IF filter, AWGN, partial-band noise jamming, the differential detector offers no theoretical performance advantage over the limiter-discriminator receiver with integrate-and-dump postdetection filtering.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-31; 1227-123
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  • 4
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    Control of large space antennas based on electromagnetic-structural models (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A general approach to the optimal control of large space antennas based on their RF/structural characteristics is described. The approach consists of defining a cost functional based on the degradation of the RF performance of the antenna and using the structural model as the dynamic system. The method is applied to the design of an optimal controller for a 55-m, wrap-rib offset-fed antenna. The controller's goal is to minimize the variations of the peak electric field of the antenna due to feed displacements.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 181-194
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  • 5
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    DSN ground communications facility (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A functional description of the GCF and its relationships with other elements of the DSN and NASCOM is presented together with development objectives and goals and comments on implementation activites in support of flight projects.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 200-209
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  • 6
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    MV-3 communication subsystem (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The operational mobile VLBI data acquisition system (MV-3) requires that a voice link be established between the mobile data system and a fixed site. A communications subsystem was incorporated in the MV-3 design which consists of HF radio, VHF mobile radio telephone and conventional land line telephone. The HF antenna design was optimized for short and long range transmission using both inverted V and yagi antennas mounted on a self-supporting telescoping mast.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 210-219
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  • 7
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    S-band aperture efficiency of the DSS 13 26-meter antenna with the S-X common aperture feed (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Measurements of the S-band performance of the DSS 13 26-meter antenna, equipped with the second generation S-X common aperture feed, are reported. Aperture efficiency and overall antenna gain results are compared with predicted values. The elevation dependence of the aperture efficiency is reported.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 89-94
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  • 8
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    Antenna arraying performance for deep space telecommunications systems (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Antenna arraying is a crucial Deep Space Network technique in maximizing the science return of planetary and comet encounters. The equations which describe the total figure of merit for a multiple system of arrayed antennas are developed. An example is given for three Canberra DSN antennas and the Parkes 64-m antenna to be arrayed for the Voyager 2 Uranus flyby.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 83-88
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  • 9
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    VLBI collimation tower technique for time-delay studies of a large ground station communications antenna (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A need for an accurate but inexpensive method for measuring and evaluating time delays of large ground antennas for VLBI applications motivated the development of the collimation tower technique. Supporting analytical work which was performed primarily to verify time delay measurement results obtained for a large antenna when the transmitter was at a collimation distance of 1/25 of the usual far field criterion is discussed. Comparisons of theoretical and experimental results are also given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 20-29
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  • 10
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    A near-optimum receiver structure for the detection of M-ary optical PPM signals (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: A class of receivers called conditionally nulling receivers is defined for quantum noise limited optical communications. These receivers have the ability to decide at each moment in time whether or not to coherently combine a predetermined local oscillator field with the received optical field, prior to performing an energy measurement (photodetection) on the combined field. Conditionally nulling receivers are applicable to pulse position modulation and related modulation schemes, which have the property that, at each moment in time, the transmitted signal is in one of only two states, on or off. The local oscillator field which may or may not be added by the receiver is an exact replica of the negative of the received on field; hence, the receiver can exactly null the on signal if the on signal is present and the receiver chooses to use the local field. An ideal conditionally nulling receiver achieves very nearly the same error probability (within a multiplicative factor varying froom 1 to 2.15) as the optimum quantum measurement for quantum noise limited detection of M-ary PPM signals. In contrast, other known receiving methods, such as direct, heterodyne, and homodyne detection, are exponentially suboptimum.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 30-42
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  • 11
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    Standard format data units - Tools for automatic exchange of space mission data (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A set of standard formatting rules for the data sets, and a standard computer-readable language with which to describe the data, are two tools which are used to create the Standard Format Data Unit (SFDU). The NASA/JPL proposal for creation and utilization of SFDUs is presented, and its relationship to recommendations from the Consultative Committee for Space Data Systems (CCSDS) is discussed. Several current and planned implementations of the SFDU concept among major space flight projects are identified. The purpose of creating the concept of an SFDU is to allow members of the science community to share national and global resource data independently of project or program. The feedback from SFDU implementation efforts is considered an essential part of the CCSDS activity. Even though the CCSDS specifically deals with space data systems, the SFDU concept can be applied to practically every data system on an open network. The SFDU is in the early phase of CCSDS standard definition work, and must go through several other phases before being formally recommended as an international standard.
    Keywords: COMMUNICATIONS AND RADAR
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  • 12
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    Control of antenna-feed attitude and reflector vibrations in large spaceborne antennas by mechanical decoupling and movable dampers (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Simple, practical methods for damping reflector vibrations and designing antenna-feed attitude control systems in large deployable spaceborne antennas are proposed. The former involves a movable damper which is positioned so that the rate-of-change of total vibrational energy is minimized. The latter introduces a mechanical decoupler between the flexible boom and the antenna-feed, whereby the feed-attitude control system can be designed independent of boom dynamics. The validity of these approaches are substantiated by analytical studies, computer simulation, and experimental studies.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 143-161
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  • 13
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    Beam forming networks for mm-wave satellite communications (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Technology features of a beam forming network (BFN) employing ferrite devices to provide multiple beam antenna pattern control for satellites used in telecommunications are described. The BFN produces the phase and amplitude distribution for each horn in an antenna array, with the number of horns in the array being equal to the number of outputs in the BFN. One configuration involves microwave switches and permits illumination of a single feed horn at a time using ferrite latching circulators that function by reversing the circulation direction. A more flexible version, yielding a variable amplitude distribution across the feed horn array to accommodate changing traffic patterns or serving a TDMA system, includes the capability of forming nulls in the system with a variable phase shifter in the input ports. The antenna scan angles in phased arrays can be limited to 8 deg from center. Acceptable insertion losses have been demonstrated in BFN with hundreds of ports and switching rates as high as 10 kHz.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Microwave Journal (ISSN 0026-2897); 26; Aug. 198
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  • 14
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    Signal processing of anthropometric data (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Anthropometric Measurements Laboratory has accumulated a large body of data from a number of previous experiments. The data is very noisy, therefore it requires the application of some signal processing schemes. Moreover, it was not regarded as time series measurements but as positional information; hence, the data is stored as coordinate points as defined by the motion of the human body. The accumulated data defines two groups or classes. Some of the data was collected from an experiment designed to measure the flexibility of the limbs, referred to as radial movement. The remaining data was collected from experiments designed to determine the surface of the reach envelope. An interactive signal processing package was designed and implemented. Since the data does not include time this package does not include a time series element. Presently the results is restricted to processing data obtained from those experiments designed to measure flexibility.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Johnson (Lyndon B.) Space Center The 1983 NASA/ASEE Summer Faculty Fellowship Research Program Research Reports; NASA. Johnson (Lynd
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  • 15
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    Chung-Li, Taiwan dual mode (Doppler and spaced antenna) VHF radar: Preliminary specifications (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A major unresolved question in the field of atmospheric research using VHF radar techniques is the relative merit of the two most widely used systems. These systems are the Doppler method and the spaced antenna method. It has been suggested that one radar of each type be operated side by side for a direct comparison of the two techniques. This duplication of effort is not cost effective. The major components of both systems are identical, and one radar could be operated in both modes by proper design of a suitable antenna system and by proper data analysis. The Chung-Li radar will be able to switch between modes on a time scale of seconds and is the first VHF radar to be able to directly compare the Doppler data with spaced antenna data. The system will have performance comparable with the present SOUSY spaced antenna system and will provide mesospheric data in addition to stratospheric and tropospheric data. The major specifications of the Chung-Li radar are given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 383-386
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  • 16
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    Capabilities and limitations of existing MST radars: Colorado wind profilers (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Wave Propagation Laboratory is developing a ground-based remote sensing system called PROFILER to measure troposphere parameters currently measured in operational meteorology by radiosondes. The prototype PROFILER uses two radars for wind sounding: a 6-m radar located at Platteville, Colorado, and a 33-cm radar located at Denver's Stapleton International Airport. In addition, a network of three 6-m wind-profiling radars is being installed in Colorado, and a fourth site is planned. The location of the five radars, their characteristics, and their limitations are described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 325-329
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  • 17
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    Capabilities and limitations of EISCAT as an MST radar (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The European Incoherent Scatter Radar Facility also has facilities which can be used for coherent scatter research of the middle atmosphere. The observatory consists of two independent systems which allow observations of the upper, middle, and lower atmosphere: a tristatic UHF radar capable of vector drift measurements, and a monostatic VHF system. The characteristics of the components are are described including inter-site communication, on-line displays, and the real-time operating system. Analysis of about 60 hours of middle atmosphere observations in 1982 indicate that EISCAT's capabilities to measure mesospheric parameters should improve during moderately or strongly disturbed conditions, enabling measurement of profiles of wind velocity, electron density, and temperature/collision frequency, and in some instances, ion masses. Because of not yet optimized transmit-receive switching, some limitations exist in the monostatic mode when observing coherent scattering in the stratosphere at short ranges.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 305-314
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  • 18
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    The spaced antenna drift method (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: The spaced antenna drift method is a simple and relatively inexpensive method for determination of atmospheric wind velocities using radars. The technique has been extensively tested in the mesosphere at high and medium frequencies, and found to give reliable results. Recently, the method has also been applied to VHF observations of the troposphere and stratosphere, and results appear to be reliable. This paper discusses briefly the principle of the method, and investigates both its strengths and weaknesses. Some discussions concerning criticisms of the technique are also given, and it is concluded that while these criticisms may be of some concern at times, appropriate care can ensure that the method is at least as viable as any other method of remote wind measurement. At times, the technique has definite advantages.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 171-186
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  • 19
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    Techniques for measurements of horizontal and vertical velocities (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Spectrum analysis and correlation methods used to measure the horizontal and vertical velocities of radar echo signals are examined mathematically. Topics include scattering/reflection geometry, monostatic versus bistatic operation, spaced antenna measurements, radar interferometry and the Doppler method. Vertical velocity determination, optimum pointing angles, and time resolution for periodic variations are also investigated.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 150-163
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  • 20
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    Spectral characteristics of the return (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: Doppler spectra of VHF radar returns typically indicate a Gaussian back-ground shape with superimposed spikes. An average of 10 Doppler spectra are shown which are calculated from a time series of seven min of complex data. A proper Gaussian fit to the background distribution is possible by neglecting the strong amplitude spikes. If this background distribution is due to beam width broadening, either diffuse reflection or rather isotropic scattering is required. If beam width broadening is neglected, the width of the distribution is given by turbulent velocity fluctuations. The reflected component is about 1/3 of the scattered component. It is assumed that the amplitude spikes due to diffuse reflection indicate a Gaussian frequency distribution such as for the amplitudes due to scattering.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 112-113
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  • 21
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    The effects of pulse rate, power, width and coding on signal detectability (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The effects on the signal detectability of varying the pulse repetition rate (PRF), peak pulse power (p(pk)) and pulse width (tau(p)) (tp) are examined. Both coded and uncoded pulses are considered. The following quantities are assumed to be constant; (1) antenna area, (z)echo reflectivity, (3) Doppler shift, (4) spectral width, (5) spectral resolution, (6) effective sampling rate, and (7) total incoherent spectral averagaing time. The detectability is computed for two types of targets.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 100-104
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  • 22
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    Is VHF Fresnel reflectivity due to low frequency buoyancy waves? (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: VHF radar echoes are greatly enhanced near the zenith relative to other directions. This enhancement must be due to reflection from horizontally stratified laminate of refractive index. The refractivity laminate are due to the displacements of low frequency buoyancy (internal gravity) waves acting on the background vertical gradient of refractivity. VANZANDT (1982) has shown that the observed spectra of mesoscale wind fluctuations in the troposphere and lower stratosphere are modeled by a universal spectrum of buoyancy (internal gravity) waves. Since the observed frequency spectrum is red, the buoyancy wave model of the vertical displacement spectrum is strongly enhanced near the zenith. In other terms, the resulting refractivity irregularities are strongly stratified.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 78-80
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  • 23
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    Parmeterization of spectra (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: Following reception and analog to digital conversion (A/D) conversion, atmospheric radar backscatter echoes need to be processed so as to obtain desired information about atmospheric processes and to eliminate or minimize contaminating contributions from other sources. Various signal processing techniques have been implemented at mesosphere-stratosphere-troposphere (MST) radar facilities to estimate parameters of interest from received spectra. Such estimation techniques need to be both accurate and sufficiently efficient to be within the capabilities of the particular data-processing system. The various techniques used to parameterize the spectra of received signals are reviewed herein. Noise estimation, electromagnetic interference, data smoothing, correlation, and the Doppler effect are among the specific points addressed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 535-542
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  • 24
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    Parameterization of spectrum (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: Many radars used for wind sounding generate Doppler power spectra as output. For compact data archiving purposes, as well as for data analysis, several parameters were produced to characterize each spectrum. The parameters chosen were noise level, echo signal strength, velocity, and width. Because the derived parameters may be the only quantities available for future analysis, it was important that they did not contain biases imposed by the derivation techniques. This consideration led to a processing scheme in which the parameters were derived independently for each spectrum.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 546-547
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  • 25
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    Data analysis techniques: Spectral processing (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The individual steps in the data processing scheme applied to most radars used for wind sounding are analyzed. This processing method uses spectral analysis and assumes a pulse Doppler radar. Improvement in the signal to noise ratio of some radars is discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 528-531
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  • 26
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    Full versus limited versus no steerability (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: The range of phenomena of the MST radar technique to divide the steerability versus nonsteerability problem into two broad with a third subset that lies between these two limits are studied. Processes that vary on a horizontal scale which are comparable to the area of the probing radar beam can best be fully steerable beams. The use of fixed beam systems would be a long term study of the mean wind field. Orographic effects due to mountain ridges and/or land-sea interfaces demand steerable beams, particularly if the effects are three dimensional in character. In view of their lack of moving parts fixed beam systems are more reliable. It is assumed that the reliability of a system is inversely proportioned to the number of moving parts. This is not a problem for fixed beam systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 463-464
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  • 27
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    Directivity and spacing for the antenna elements (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: The optimum design choice for the MST radar antenna was considered. The following factors are required: directivity and gain; beam width and its symmetry; sidelobe levels, near and wide angle; impedance matching; feeder network losses; polarization diversity; steerability; cost effectiveness; and maintainability. The directivity and related beam forming aspects of various antenna elements and directivity aspects when such elements are formed into an array are discussed. Array performance for important variables, in particular, the spacing of the elements is considered.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 456-462
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  • 28
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    Design considerations for high-power VHF radar transceivers: T/R switch design (1983)
    In:  Other Sources
    Details
    Publication Date: 2016-06-07
    Description: The transceiver (TR) switch developed at NOAA's Aeronomy Laboratory for use in their 50 kW peak power, 50 MHz transmitter is described. The switch mounts inside the transmitter chassis and was designed to be compact while retaining the ability to handle well over 50 kW peak power at average power levels up to 2 kW. The TR switch is a conventional TR/ATR design with equivalent /4 transmission line sections constructed of lumped constant coils and transmitting capacitors in ''Tee' sections. Two TR sections are placed in series to achieve adequate receiver protection. The switch is set into the ''transmit' mode by forward biasing the 3 pin diodes to about 1.2 amperes each. The receive mode is achieved by back biasing the diodes to -15 volts. A directional coupler is also incorporated into the TR switch box to provide a convenient monitor point for forward and reflected transmitter power.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 431-432
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  • 29
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    A transceiver module of the Mu radar (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The transceiver (TR) module of a middle and upper atmospheric radar is described. The TR module used in the radar is mainly composed of two units: a mixer (MIX unit) and a power amplifier (PA unit). The former generates the RF wave for transmission and converts the received echo to the IF signal. A 41.5-MHz local signal fed to mixers passes through a digitally controlled 8-bit phase shifter which can change its value up to 1,000 times in a second, so that the MU radar has the ability to steer its antenna direction quickly and flexibly. The MIX unit also contains a buffer amplifier and a gate for the transmitting signal and preamplifier for the received one whose noise figure is less than 5 dB. The PA unit amplifies the RF signal supplied from the MIX unit up to 63.7 dBm (2350 W), and feeds it to the crossed Yagi antenna.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 421-423
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  • 30
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    Decoders for MST radars (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Decoding techniques and equipment used by MST radars are described and some recommendations for new systems are presented. Decoding can be done either by software in special-purpose (array processors, etc.) or general-purpose computers or in specially designed digital decoders. Both software and hardware decoders are discussed and the special case of decoding for bistatic radars is examined.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 416-420
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    The Urbana MST radar, capabilities and limitations (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The 41-MHz coherent-scatter radar located northeast of the University of Illinois at Urbana is being used for studies of the troposphere, stratosphere and mesosphere regions. The antenna consists of 1008 halfwave dipoles with a physical aperture of 11000 sq m. Transmitted peak power is about 750 kW. Clear-air returns may be received from 6 km to 90 km altitude. Autocorrelation functions of the scattered signal are calculated on-line. From the autocorrelation functions the scattered power, line-of-sight velocity and signal correlation time are calculated. Some aspects of the troposphere/stratosphere and the mesosphere observations are discussed. Capabilities and limitations of the Urbana MST radar are pointed out, and recent and planned improvements to the radar are described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 346-356
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  • 32
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    A comment on some drawbacks of monostatic radars (1983)
    In:  Other Sources
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    Publication Date: 2016-06-07
    Description: All Mesosphere, Stratosphere, Troposphere (MST) radars now in operation or under construction use the monostatic mode, that is to say, the same antenna for both transmitting and receiving. Consequently, it is never possible to determine more than one component of the atmospheric velocity at one point in space. Two important properties of gravity waves which are difficult if not impossible to determine by the monostatic method are discussed. The first of these is the polarization of the gravity waves; that is, the complex ratio of the wave functions of vertical and horizontal motion. A second quantity of importance is the horizontal wavelength of gravity waves. Both of these problems could be overcome by use of a bistatic system. Such a system has the additional advantage of making it possible to measure at very low altitudes, and to look away from the transmitter (for example to make a horizontal section through a thunderstorm). However, bistatic operation, in the practical sense, requires not only an additional highly directive antenna, but also that both the transmitting and receiving antennas should be fully steerable.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 170
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    Techniques for measurement of vertical and horizontal velocities: Monostatic versus bistatic measurements (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Three techniques of direct measurement are presented from which velocities may be obtained: (1) Doppler frequency shift, (2) spaced antenna drift, (3) spatially modulated transverse beam measurements. Emphasis is placed on the Doppler frequency measurement approach. It will compare bistatic with monostatic configurations as regards received power (or sensitivity), spatial resolution, Doppler shift and avoidance of ground clutter.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 164-169
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  • 34
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    The JPL 1.5-meter Clear Aperture Antenna with 84.5 Percent Efficiency (1983)
    In:  CASI
    Details
    Publication Date: 2014-09-10
    Description: The theoretical and experimental study of a 1.5-meter offset dual shaped reflector at 31.4 GHz is detailed. An efficiency of 84.5 percent, a likely new record for reflector antennas, was ascertained through careful measurements. For larger low noise reflector systems, a 2- to 3-dB improvement in G/T performance over the state of the art ultra low noise ground stations and 90 percent or better aperture efficiency now appear feasible.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 1-14
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  • 35
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    Gain Stability Measurements at S-band and X-band (1983)
    In:  CASI
    Details
    Publication Date: 2014-09-12
    Description: The Search for Extraterrestrial Intelligence (SETI) requires low noise broadband total power radiometers of high gain stability. Preliminary results of SETI field tests for a variety of receiver configurations at Deep Space Station 13 are discussed. The power spectra of Deep Space Network low noise receiving systems exhibit I/F noise whose spectral index is significantly smaller than unity. The gain stability of the S-band systems tested is almost 0.0001. An appendix presents a derivation of the power spectrum of the output of a square law detector.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 159-168
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  • 36
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    Planetary Radar (1983)
    In:  CASI
    Details
    Publication Date: 2014-09-12
    Description: The application of modern planetary radar techniques to a comet passing in close proximity to Earth is discussed. These techniques have the potential to determine the nature of cometary origins, structure, and internal dynamics. Moreover, the understanding gained could very likely negate or corroborate one of the prevailing hypotheses regarding the origin of the solar system: that comets are the remainder of the primordial out of which the planets coalesced approximately 4.5 billion years ago. In 1983, two unique opportunities were presented to observe a comet very near to Earth. The last such encounter was several centuries ago.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 114-115
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  • 37
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    Atmospheric Effects (1983)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: The Earth's atmosphere consists mostly of the dry components oxygen (about 21% by volume), nitrogen (about 78% by volume) argon (about 1% by volume), and wet components (water vapor, clouds and rain). Water vapor at 100% relative humidity is approximately 1.7% by volume assuming the U.S. Standard Atmosphere, 15 C, at sea level. A communications link through the atmosphere suffers attenuation from both the dry and wet components. This results in a decreased signal to noise ratio (SNR) of the communications link due to both the signal attenuation and the increased noise temperature resulting from thermal emission.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Deep Space Network: A Radio Commun. Instr. for Deep Space Exploration; 18 p
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  • 38
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    The System View (1983)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: Analysis of spacecraft to ground communications link performance and a description of the Deep Space Network system is provided. Due to the tremendous distances involved in communicating between the spacecraft at the edge of our solar system and Earth, communications link performance is stretched to the limit of theoretical predictions. This is required in order to return the maximum amount of data possible during critical events such as planetary flybys. The link analysis provides a basis for the initial link design before spacecraft launch and performance prediction and monitoring during spacecraft flight. Additionally, it indicates what performance upgrades are required for mission extensions and new missions. Performance is improved through the use of a larger antenna collecting area, greater transmitter power, lower receiving system noise temperature and more sophisticated data coding schemes. The performance of the Deep Space Station configuration which serves as the ground portion of the communications link is assessed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Deep Space Network: A Radio Commun. Instr. for Deep Space Exploration; 25 p
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  • 39
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    New Directions: 1982-2000 (1983)
    In:  CASI
    Details
    Publication Date: 2014-09-10
    Description: The major objective of the Deep Space Network in the period 1983-2000 is the fulfillment of the extremely diverse telecommunications requirements of the known and anticipated users. Deep space exploration projects will continue to occupy a dominant role, although in the mid-1980s, with the completion of the Networks Consolidation Program, high Earth orbiter projects will become substantial users of the Network. Also playing an increasingly important role in the Network of the next decade will be non-flight projects, such as Geodynamics, Radio Astronomy, Radar Astronomy, and the Search for Extraterrestrial Intelligence (SETI). The major challenge in meeting the primary Network objective of the next decade will be that of providing increased performance as required by users at costs which can be borne by NASA in an environment of limited resources. Emphasis will be on increased commonality, flexibility, and automation to reduce maintenance and operations costs, and lower mission costs.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Deep Space Network: A Radio Commun. Instr. for Deep Space Exploration; 21 p
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  • 40
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    Command (1983)
    In:  CASI
    Details
    Publication Date: 2014-09-10
    Description: The Command System provides the means by which a project controls the activities of its spacecraft from the Earth. An overview of the Multimission Command (MMC) System is presented. The major components within the MMC System are discussed, with emphasis on the telecommunications related implementations. Two versions of the spacecraft command detection system the Viking Heritage command detector and the NASA standard command detector are summarized. The former prevails in the existing flight projects and the latter will likely be adopted by the missions of the near future. The preparation of Design Control Tables for the control of command link performance between Deep Space Stations and the spacecraft is also discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Deep Space Network: A Radio Commun. Instr. for Deep Space Exploration; 24 p
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  • 41
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    Developments Related to the Future Use of the 32-ghz Allocation for Deep Space Research (1983)
    In:  CASI
    Details
    Publication Date: 2014-09-10
    Description: The advantage of 32-GHz links, the estimated link performance, and developments in the fields of antennas, low noise preamplifiers, radiometry, and propagation studies are discussed. A description of ways to demonstrate 32-GHz link capability concludes the discussion.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 165-175
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  • 42
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    Shuttle Imaging Radar: A/B sensors (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The exciting discoveries of the Shuttle Imaging Radar-A (SIR-A) experiment prompted a refly of the instrument to be designated the Shuttle Imaging Radar-B. The SIR-B instrument will reuse the hardware flown for the SIR-A mission and add some interesting refinements. The two radar sensors are described in detail. The SIR-A and SIR-B instruments are both tailored for use on the Space Shuttle. They are physically configured to fit in the Shuttle's payload bay, are powered and cooled by shuttle systems, are controlled by the crew or from the ground, and record data on board or beam it to the ground using the orbiter's data links. The radars are designed to accommodate a range of orbiter altitudes and have built in operating modes to cover a wide variety of mission objectives. The flexibility and utility of these radars make them ideal, cost effective instruments for research in the Space Shuttle environment.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 26-31
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  • 43
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    The finite ground plane effect on the microstrip antenna radiation patterns (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The uniform geometrical theory of diffraction (GTD) is employed for calculating the edge diffracted fields from the finite ground plane of a microstrip antenna. The source field from the radiating patch is calculated by two different methods: the slot theory and the modal expansion theory. Many numerical and measured results are presented to demonstrate the accuracy of the calculations and the finite ground plane edge effect.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-31; July 198
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    An algorithm for the empirical optimization of antenna arrays (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A numerical technique is presented to optimize the performance of arbitrary antenna arrays under realistic conditions. An experimental-computational algorithm is formulated in which n-dimensional minimization methods are applied to measured data obtained from the antenna array. A numerical update formula is used to induce partial derivative information without requiring special perturbations of the array parameters. The algorithm provides a new design for the antenna array, and the method proceeds in an iterative fashion. Test case results are presented showing the effectiveness of the algorithm.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-31; July 198
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  • 45
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    Capacity limit of the noiseless, energy-efficient optical PPM channel (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: It is shown that even though the capacity per photon can be made to increase without bound, the capacity per channel use (for best power efficiency) is always less than 2 nats per symbol. Furthermore, it approaches 2 nats per symbol as the bandwidth expansion factor goes to infinity. Previously announced in STAR as N82-20121
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-31; April 19
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  • 46
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    Observations of internal waves in the Gulf of California by SEASAT SAR (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Internal waves which are among the most commonly observed oceanic phenomena in the SEASAT SAR imagery are discussed. These waves are associated with the vertical displacements of constant water density surfaces in the ocean. Their amplitudes are maximum at depths where the water density changes most rapidly usually at depths from 50 to 100 m, whereas the horizontal currents associated with these waves are maximum at the sea surface where the resulting oscillatory currents modulate the sea surface roughness and produce the signatures detected by SAR.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 118-120
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    Performance evaluation of the JPL interim digital SAR processor (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The performance of the Interim Digital SAR Processor (IDP) was evaluated. The IDP processor was originally developed for experimental processing of digital SEASAT SAR data. One phase of the system upgrade which features parallel processing in three peripheral array processors, automated estimation for Doppler parameters, and unsupervised image pixel location determination and registration was executed. The method to compensate for the target range curvature effect was improved. A four point interpolation scheme is implemented to replace the nearest neighbor scheme used in the original IDP. The processor still maintains its fast throughput speed. The current performance and capability of the processing modes now available on the IDP system are updated.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 93-95
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  • 48
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    Processor architecture for airborne SAR systems (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Digital processors for spaceborne imaging radars and application of the technology developed for airborne SAR systems are considered. Transferring algorithms and implementation techniques from airborne to spaceborne SAR processors offers obvious advantages. The following topics are discussed: (1) a quantification of the differences in processing algorithms for airborne and spaceborne SARs; and (2) an overview of three processors for airborne SAR systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 89-92
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  • 49
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    Slotted waveguide array antennas for spaceborne SAR applications (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Starting with mission definitions and constraints for the NASA proposed Shuttle Active Microwave Experiments (SAMEX) and Free Flying Imaging Radar Experiment (FIREX), Hughes Aircraft Company has compiled and studied the technology available for slotted waveguide planar array antennas suitable for spaceborne SAR application. Antenna performance is derived, and fabrication techniques are discussed. Mission requirements will always lead to an aperture subdivided into waveguide modules, thereby validating a module definition for other mission building blocks. Finally, a specific design is proposed for a SAMEX mission using the modules as RF aperture building blocks, resulting in a (nominal) 15.1 meter by 5.5 meter extensile dual polarized L-, C-, and X-band planar array with an associated extensile graphite/epoxy support structure. Antenna development begin with a fabrication method development study involving a representative portion of an antenna module.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 35-40
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  • 50
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    Geologic application of spaceborne radars (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Geologic applications of spaceborne radar images, specifically SEASAT in southern California and SIR-A in Indonesia are illustrated.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 5-9
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  • 51
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    Real-time synthetic aperture radar image formation utilizing an electrooptic spatial light modulator (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The development of novel electro-optic spatial light modulators (both one and two dimensional) which allows real-time coherent optical SAR processors to be implemented is outlined. It is suggested that the availability of such processors may initiate new mission applications not presently envisioned due to current digital processor limitations.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 107-109
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    Radar activities of the DFVLR Institute for Radio Frequency Technology (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Aerospace research and the respective applications microwave tasks with respect to remote sensing, position finding and communication are discussed. The radar activities are directed at point targets, area targets and volume targets; they center around signature research for earth and ocean remote sensing, target recognition, reconnaissance and camouflage and imaging and area observation radar techniques (SAR and SLAR). The radar activities cover a frequency range from 1 GHz up to 94 GHz. The radar program is oriented to four possible application levels: ground, air, shuttle orbits and satellite orbits. Ground based studies and measurements, airborne scatterometers and imaging radars, a space shuttle radar, the MRSE, and follow on experiments are considered.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 136-139
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    Spaceborne radar research in the 1980's (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The SEASAT SAR and Shuttle Imaging Radar SIR-A experiments demonstrated that spaceborne synthetic aperture radars provide synoptic images of land and ocean features. Radar images clearly show geologic structures, morphologic features, clear cutting, subsurface features (in very arid regions), agricultural and urban land use, ocean surface waves, current boundaries, internal waves, ice floes and numerous other ocean features which affect the surface roughness.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 131-135
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  • 54
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    Radar image interpretation techniques applied to sea ice geophysical problems (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The geophysical science problems in the sea ice area which at present concern understanding the ice budget, where ice is formed, how thick it grows and where it melts, and the processes which control the interaction of air-sea and ice at the ice margins is discussed. The science problems relate to basic questions of sea ice: how much is there, thickness, drift rate, production rate, determination of the morphology of the ice margin, storms feeling for the ice, storms and influence at the margin to alter the pack, and ocean response to a storm at the margin. Some of these questions are descriptive and some require complex modeling of interactions between the ice, the ocean, the atmosphere and the radiation fields. All involve measurements of the character of the ice pack, and SAR plays a significant role in the measurements.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 116-117
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    Stereo imaging with spaceborne radars (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Stereo viewing is a valuable tool in photointerpretation and is used for the quantitative reconstruction of the three dimensional shape of a topographical surface. Stereo viewing refers to a visual perception of space by presenting an overlapping image pair to an observer so that a three dimensional model is formed in the brain. Some of the observer's function is performed by machine correlation of the overlapping images - so called automated stereo correlation. The direct perception of space with two eyes is often called natural binocular vision; techniques of generating three dimensional models of the surface from two sets of monocular image measurements is the topic of stereology.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 53-55
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    Use of coregistered radar, visible and IR images for geologic remote sensing (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The Shuttle Imaging Radar (SIR-A) obtained images over the southern portion of the San Rafael Swell in eastern Utah. SEASAT SAR and LANDSAT MSS images and thermal inertia data from the Heat Capacity Mapping Mission (HCMM) were correlated with the SIR-A data. Radar images obtained with different incidence angles and different illumination directions were compared with images obtained in other portions of the spectrum for geologic remote sensing.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 13-16
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    European Space Agency, ERS-1 program (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The objectives selected for ERS-1 which are primarily intended to facilitate the exploitation of coastal oceans, including ice infested waters, and to facilitate the development of improved global weather information through the provision of information on the weather conditions over the oceans of the word are outlined. Additionally, land objectives will be addressed using the synthetic aperture radar incorporated in the payload.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 140-142
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    Mechanisms for SAR imaging of ocean surface phenomena: Theory and experiment (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Understanding the SAR response to surface wave is a central issue in the analysis of SAR ocean images. The imaging mechanism for gravity waves and the practical question of just which characteristics of the ocean wave field can be measured remotely using SAR were examined. Assessments of wave imaging theory are based primarily on comparisons of the directional wave height variance spectrum psi (K) measured by in situ buoys with estimates from SAR images. Other criteria are also recommended, e.g., the effects of focus adjustments. It is assumed that fluctuations in SAR image intensity are proportional to fluctuations in ocean surface height. If this were true, the Fourier power spectrum of a SAR image and corresponding surface measurements of psi would coincide. Differences between SAR estimates based on this hypothesis and buoy measurements of psi are then used to begin the assessment of rival wave imaging theories.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 124-127
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  • 59
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    Microstrip antennas for SAR applications (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Current and future microstrip antenna technology development for Spaceborne Synthetic Aperture Radars (SAR) are summarized. Some of the electrical and mechanical characteristics of previously and presently developed microstrip SAR antennas are shown. The SEASAT, the SIR-A and presently the SIR-B antennas are all designed for operation at L-band with approximately 22 MHz of bandwidth. The antennas have linear polarization with minimum of 20 dB of polarization purity. Both the SEASAT and SIR-A antennas were designed for a fixed pointing angle of 20.5 deg and 47 deg, respectively. However, the SIR-B has the added feature of mechanical beam steering in elevation (range). With the exception of different mechanical characteristics, it is concluded that present spaceborne SAR antennas have only single frequency and single polarization performance. The lack of large spaceborne antennas operating at the higher degree of fabrication tolerance required for a given performance; and larger feed and radiating element losses.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 32-34
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    A fast, programmable hardware architecture for spaceborne SAR processing (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The launch of spaceborne SARs during the 1980's is discussed. The satellite SARs require high quality and high throughput ground processors. Compression ratios in range and azimuth of greater than 500 and 150 respectively lead to frequency domain processing and data computation rates in excess of 2000 million real operations per second for C-band SARs under consideration. Various hardware architectures are examined and two promising candidates and proceeds to recommend a fast, programmable hardware architecture for spaceborne SAR processing are selected. Modularity and programmability are introduced as desirable attributes for the purpose of HTSP hardware selection.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 99-104
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    Spaceborne SAR and sea ice (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A number of remote sensing systems deployed in satellites to view the Earth which are successful in gathering data on the behavior of the world's snow and ice covers are described. Considering sea ice which covers over 10% of the world ocean, systems that have proven capable to collect useful data include those operating in the visible, near-infrared, infrared, and microwave frequency ranges. The microwave systems have the essential advantage in observing the ice under all weather and lighting conditions. Without this capability data are lost during the long polar night and during times of storm passage, periods when ice activity can be intense. The margins of the ice pack, a region of particular interest, is shrouded in cloud between 80 and 90% of the time.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 113-115
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    Real-time digital processing of SAR data (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Current SAR data processing techniques for spaceborne SAR systems utilize commercial equipment to carry the computation load. For a data set such as SEASAT, the resulting throughput rate is two to three orders of magnitude slower than real time. Such rates impede the progress of scientific investigations and preclude the potential for any practical operational SAR mission. It is suggested that a set of special-purpose hardware could be designed for efficient SAR data processing so that real time rates are both practical and affordable.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 96-98
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    Solid state transmitters for spaceborne radars (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The SEASAT-A synthetic aperture radar, the first spaceborne SAR, utilized an all solid state RF signal synthesizer and L-band transmitter to drive a corporately fed flat plate array. The RF signal synthesizer generated a linear FM ""CHIRP'' waveform and provided stable CW reference signals used to upconvert the received signal to a unified S-band downlink channel, and to synchronize satellite control logic. The transmitter generated 1200 watts peak RF power (66 watts average) at a center frequency of 1.275 GHz from 354 watts of DC prime power. Linear FM CHIRP swept symmetrically around the center frequency with a bandwidth of 19.05 MHz and a pulse duration of 33.8 sec. Pulse repetition rate was variable from 1647 to 1944 pps. These transmitter signal parameters combined with the flat plate 34 x 7.5 ft aperture at an orbital altitude of 498 miles and a look angle 20 deg off nadir gave the SAR an 85 foot resolution over a 15.5 mile wide swath.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 41-47
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  • 64
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    Spaceborne SAR sensor architecture (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Spaceborne imaging radars for the decade of the '90s will be called upon to provide increased illumination parameter flexibility, polar orbital coverage, and to operate from the same platform with other advanced sensors such as multilinear arrays. The potential information content in accurately merged microwave infrared, or microwave visible images is enormous by comparison to either radar images alone or visible/infrared images alone, since microwave images are principally responsive to surface geometry whereas visible/infrared images are highly sensitive to surface chemistry. A strawman system concept in which a SAR and multilinear array (MLA) are flown on a polar orbiting free flyer at 800 km altitude is discussed. Data would be relayed to ground via the TDRSS (or equivalent).
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 19-25
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  • 65
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    Substance geology of the western desert in Egypt and Sudan revealed by Shuttle Imaging Radar (SIR-A) (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A correlation of known archaeologic sites with the mapped locations of the streamcourses is expected and may lead to new interpretations of early human history in the Sahara. The valley networks, faults, and other subjacent bedrock features mapped on the SIR-A images are promising areas for ground water and mineral exploration. Additionally, the analogies between the interplay of wind and running water in the geologic history of the Sahara and of Mars are strengthened by the SIR-A discoveries of relict drainage systems beneath the eolian veneer of Egypt and Sudan.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 10-12
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  • 66
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    The impact of mismatch on the performance of coded narrow-band FM with limiter/discriminator detection (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An examination of the impact of mismatch on the performance of convolutionally encoded/Viterbi decoded narrow-band FM with limiter/discriminator detection is presented. Attention was given to the potential gain available by the combination of this type of system in terms of hard and soft decision decoding. Soft decision decoding was demonstrated to offer only approximately 0.3 dB better performance than hard decision coding. It was also shown, through a technique involving the number of clicks occurring in each detection interval, that both soft and hard decision decoding bit error probability performance could be improved. It is concluded that the mismatch between the coding channel and the decoding metric of the Viterbi algorithm is responsible for reducing the difference between hard and soft decoding metrics.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications; COM-31; Jan. 198
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  • 67
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    Review of specific antenna configurations: An estimate of cost and performance versus frequency for a simple (10 Lambda)-2 clear-air radar antenna array (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The building of operational clear air radar wind profilers is discussed. The choice of operating frequency and antenna configuration for these profilers is examined. The cost and performance of a (10 lambda) 2 antenna array versus operating frequency over the range 30 to 400 MHz is compared. To simplify the comparison the array beam will be fixed and the array will be uniformly fed. Yagi and coaxial collinear (COCO) cable antennas are compared, although other configurations may be competitive. It is assumed that the array is driven by a typical 50 kW peak power, 1 kW average, power transmitter located at the array edge when calculating feedline power handling requirements and when system performance is compared. For this comparison an array aperture of (10 lambda) 2 was chosen since a one way beam width of 5 deg or less is desirable to limit beam spreading effects.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 470-476
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  • 68
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    School of Electrical Engineering. (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: The possibility of making the antenna of an MST radar too large is pointed out. It is not that the signal ceases to become stronger beyond some critical antenna size; the received scattered signal actually becomes weaker as the antenna size is increased whenever the target is in the near field, Fresnel region of the antenna. The Arecibo antenna is a case in point. It is supposed that MST work would benefit to use a feed which illuminated only a portion of the dish.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 465-466
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  • 69
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    MST radar transmitter control and monitor system (1983)
    In:  Other Sources
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    Publication Date: 2016-06-07
    Description: A generalized transmitter control and monitor card was developed using the Intel 8031 (8051 family) microprocessor. The design was generalized so that this card can be utilized for virtually any control application with only firmware changes. The block diagram appears in Figure 2. The card provides for local control using a 16 key keypad (up to 64 keys are supported). The local display is four digits of 7 segment LEDs. The display can indicate the status of all major system parameters and provide voltage readout for the analog signal inputs. The card can be populated with only the chips required for a given application. Fully populated, the card has two RS-232 serial ports for computer communications. It has a total of 48 TTL parallel lines that can define as either inputs or outputs in groups of four. A total of 32 analog inputs with a 0-5 volt range are supported. In addition, a real-time clock/calendar is available if required. A total of 16 k bytes of ROM and 16 k bytes of RAM is available for programming. This card can be the basis of virtually any monitor or control system with appropriate software.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 429-430
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  • 70
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    Design considerations for high-power VHF radar transceivers: The Poker Flat MST radar phase control system (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Sixty-four separate 50-kW peak-power transmitters are distributed throughout the 200 x 200 meter Poker Flat MST radar antenna array. The relative phase of each transmitter is automatically controlled by a 64-channel unit located in the main building at the edge of the antenna. The phase control unit is described. In operation the RF pulse from a transmitter coupler is power divided and compared with the phase reference in a mixer. The mixer output is low-pass filtered and sampled near the center of the resulting video pulse by an amplifying sample-and-hold integrated circuit. Phase control is effected by maintaining the mixer output pulse near zero volts by amplifying the sample-and-hold output which then drives the voltage-controlled phase shifter in the direction to null the mixer output. The voltage-controlled shifter achieves over 360 deg phase shift in the range from 0.7 to 24 volts. When the voltage into the shifter tracks to either voltage limit the wrap-around control resets the voltage so that the shifter is always operating within its control range.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 424-426
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  • 71
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    Design considerations for high-power VHF radar transceivers (keynote paper) (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A review and analysis of conference papers addressing the design of high power VHF radar tranceivers is presented. Specific design topics include: (1) distributed versus single transmitters; (2) coded pulses and decoder design; (3) large transmitter design considerations; and (4) T/R switch design. The topics in the discussion on future directions include the following: (1) enhanced receiver performance; (2) transmitter systems for unattended operation; (3) limitations of the current T/R switch designs; (4) data processing (is eight bits enough); and (5) new frequencies (200 MHz and/or 400 MHz).
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 403-405
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  • 72
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    Measurement of the horizontal velocity of wind perturbations in the middle atmosphere by spaced MF radar systems (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Two remote receiving sites have been set up at a distance of approx 40 km from the main MF radar system. This allows measurement of upper atmosphere winds from 60-120 km (3 km resolution) at the corners of an approximately equilateral triangle of side approx 20 km. Some preliminary data are compared through cross correlation and cross spectral analysis in an attempt to determine the horizontal velocity of wind perturbations and/or the horizontal wavelength and phase velocity of gravity waves.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 270-273
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  • 73
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    Radar interferometer measurements (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: A few attempts have been made to use MST radar interferometers in scatter probing of the ionosphere. A brief description of radar interferometer construction is given. These interferometer observations do not appear to have been successful.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 237-240
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  • 74
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    An evaluation of the accuracy of some radar wind profiling techniques (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: Major advances in Doppler radar measurement in optically clear air have made it feasible to monitor radial velocities in the troposphere and lower stratosphere. For most applications the three dimensional wind vector is monitored rather than the radial velocity. Measurement of the wind vector with a single radar can be made assuming a spatially linear, time invariant wind field. The components and derivatives of the wind are estimated by the parameters of a linear regression of the radial velocities on functions of their spatial locations. The accuracy of the wind measurement thus depends on the locations of the radial velocities. The suitability is evaluated of some of the common retrieval techniques for simultaneous measurement of both the vertical and horizontal wind components. The techniques considered for study are fixed beam, azimuthal scanning (VAD) and elevation scanning (VED).
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 192-209
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  • 75
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    Origin of refractive index fluctuations in the mesosphere as opposed to the stratosphere and troposphere (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Mesospheric echoes are strongly influenced by the electron density profile of the ionospheric D region. These echoes therefore are only observed during daylight hours or high energy particle precipitation. The turbulence occurs in layers, which often confines the radar echoes to rather thin regions of several 100 m vertical extent, although layers as thick as several kilometers are also observed. Evaluable echoes are not observed through the entire altitude region of the mesosphere for the given power aperture product. The echoes indicate temporal variation.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 143-144
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  • 76
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    Range gate dependence of specular echoes (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Some controversy has surrounded the interpretation of the enhancement of VHF radar echoes at vertical incidence (also known as partial reflections, specular reflections and Fresnel scattering) since they were reported by the Sunset and the SOUSY radars. There is little doubt as to the observational fact of this enhancement since it was observed by experimenters using at least eleven MST or ST radars. In addition to the Sunset and SOUSY radars, this result was obtained in the lower atmosphere at the Platteville, Poker Flat, Jicamarca Arecibo radars as well as the three radars of the ALPEX experiments. In the upper atmosphere, specular or partial reflections were observed. These vertical enhancements were associated with increases in the static stability of the atmosphere, with a temperature gradient in the stratosphere, were used to monitor the height of the tropopause, and were associated with the passage of fronts.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 73-77
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  • 77
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    The economics of data acquisition computers for ST and MST radars (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Some low cost options for data acquisition computers for ST (stratosphere, troposphere) and MST (mesosphere, stratosphere, troposphere) are presented. The particular equipment discussed reflects choices made by the University of Alaska group but of course many other options exist. The low cost microprocessor and array processor approach presented here has several advantages because of its modularity. An inexpensive system may be configured for a minimum performance ST radar, whereas a multiprocessor and/or a multiarray processor system may be used for a higher performance MST radar. This modularity is important for a network of radars because the initial cost is minimized while future upgrades will still be possible at minimal expense. This modularity also aids in lowering the cost of software development because system expansions should rquire little software changes. The functions of the radar computer will be to obtain Doppler spectra in near real time with some minor analysis such as vector wind determination.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 40-48
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  • 78
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    Spectral moment estimation in MST radars (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Signal processing techniques used in Mesosphere-Stratosphere-Troposphere (MST) radars are reviewed. Techniques which produce good estimates of the total power, frequency shift, and spectral width of the radar power spectra are considered. Non-linear curve fitting, autocovariance, autocorrelation, covariance, and maximum likelihood estimators are discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 548-562
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  • 79
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    Signal processing at the Poker Flat MST radar (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Signal processing for Mesosphere-Stratosphere-Troposphere (MST) radar is carried out by a combination of hardware in high-speed, special-purpose devices and software in a general-purpose, minicomputer/array processor. A block diagram of the signal processing system is presented, and the steps in the processing pathway are described. The current processing capabilities are given, and a system offering greater coherent integration speed is advanced which hinges upon a high speed preprocessor.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 532-534
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  • 80
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    Properties of echo spectra observed by MST radars (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Turbulent scatter and Fresnel reflection are the fundamental echoing mechanisms to interpret the signals observed by Mesosphere-stratosphere-troposphere (MST) radars. Turbulent scattered echoes provide information about the turbulence structure and mean flow of the atmosphere. Observational results with VHF MST radars, however, show the importance of Fresnel reflection due to the infinite gradient of reflectivity at the edges of a scattering layer. This condition is excluded for the weak fluctuation models but it is still possible to include the observed aspect sensitivity by assuming an anisotropic structure of fluctuations. Another explanation of the aspect sensitivity observed by MST radars is advanced. Spectral estimates by the widely used periodogram were related to a four-dimensional spectrum of atmospheric fluctuations with anisotropic structure. Effects of the radar system such as antenna beam width, beam direction and Fast Fourier Transformations (FFT) data length were discussed for the anisotropic turbulent atmosphere. Echo parameters were also estimated.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol.
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  • 81
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    Correlation methods (1983)
    In:  Other Sources
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    Publication Date: 2016-06-07
    Description: A method for processing complex radar data with a computer using correlation functions is reviewed. Parameters including data storage, data reduction, and real time operation are addressed. Since complex auto- and cross-correlation functions are calculated and stored, almost no information is lost. These also can be analyzed in terms of the full correlation analysis of the spaced-antenna-drifts technique. The proposed approach therefore appears to be very feasible to suit most Mesosphere-Stratosphere-Troposphere (MST) radar applications.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 527
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  • 82
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    Complementary code and digital filtering for detection of weak VHF radar signals from the mesoscale (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The SOUSY-VHF-Radar operates at a frequency of 53.5 MHz in a valley in the Harz mountains, Germany, 90 km from Hanover. The radar controller, which is programmed by a 16-bit computer holds 1024 program steps in core and controls, via 8 channels, the whole radar system: in particular the master oscillator, the transmitter, the transmit-receive-switch, the receiver, the analog to digital converter, and the hardware adder. The high-sensitivity receiver has a dynamic range of 70 dB and a video bandwidth of 1 MHz. Phase coding schemes are applied, in particular for investigations at mesospheric heights, in order to carry out measurements with the maximum duty cycle and the maximum height resolution. The computer takes the data from the adder to store it in magnetic tape or disc. The radar controller is programmed by the computer using simple FORTRAN IV statements. After the program has been loaded and the computer has started the radar controller, it runs automatically, stopping at the program end. In case of errors or failures occurring during the radar operation, the radar controller is shut off caused either by a safety circuit or by a power failure circuit or by a parity check system.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 338-343
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  • 83
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    Capabilities and limitations of the Jicamarca radar as an MST radar (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Jicamarca radar (Long. 76.52W, Lat. 11.56S), located at 20 km from Lima at approximately 500 meters over sea level, is surrounded by mountains which provide a good shield from man-made interference. The radio horizon goes from a few hundred meters, across the dry valley where it is located, to 15 km, along the valley in the direction of the continental divide. This limits the clutter to 15 km, except for one high peak at 21 km. It is the most equatorial of all existing MST radars. Its proximity to the Andes, makes its location unique for the study of lee waves and orographic-induced turbulence. Vertical as well as horizontal projections of MST velocities are obtained by simultaneously pointing with different sections of the antenna into three or four different directions. The transmitters, receivers, and systems for data acquisition, processing, and control are included.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 315-319
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  • 84
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    Parametrization of Fresnel returns (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: It appears appropriate to use the intensity correlation function to investigate variations of a reflected signal component, and a scattered signal component, because it is determined by the relative motions, i.e., fluctuations of structual changes. An example of a correlation function is shown which can be separated into three parts: (1) a very fast drop between zero and the neighboring lag which is due to uncorrelated noise; (2) a smooth decrease at small large up to a few seconds which is due to scattering (this decrease can be approximated by a parabola); (3) a rather slow fadeout which is due to Frensel reflection and very gradually approaches zero correlation for longer lags. The noise contribution (part 1) must be eliminated by normalizing the correlation function by means of the zero-lag value which follows from a parabolic approximation. As signal intensity variations are directly connected to turbulent variations in a scattering medium or the changes of a reflecting discontinuity, parts (2) and (3) of the normalized correlation functions in terms of characteristic structure parameters, are evaluated.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 286-288
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  • 85
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    Signal processor architecture for backscatter radars (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: Real time signal processing for backscatter radars which requires computational throughput and I/O rates is discussed. The operations that are usually performed in real time are highly repetitive simple accumulations of samples or of products of samples. The control logic does not depend on the values of the data and general purpose computers are not required for the initial high speed processing. The implications of these facts on the architectures of preprocessors for backscatter radars are explored and applied to the design of the Radar Signal Compender.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 513-519
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  • 86
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    Delay line and mutual coupling considerations for MST radar antenna arrays (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: Basic antenna theory which states that the field radiated from an antenna array is equal to the sum of the currents flowing in each element of the array is discussed. The feedline distribution system guarantees the proper amplitude and phase of the current for each element of an array. The difference in electrical lengths of the feedlines to the elements has to equal the desired phase angle. The current for voltage delay in a transmission line is equal to the transmission line electrical length in only a few special cases, when the transmission line is terminated in its characteristic impedance or when the transmission line's electrical length is a multiple of 90 degrees.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 467-469
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  • 87
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    The mobile Sousy-Doppler radar: Technical design and first results (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A mobile VHF Doppler system was developed. The electronic part is installed in a 20 ft container and tested using a special log periodic aerial to illuminate the 300 m dish. The system was extended by designing a mobile phased antenna array with finally 576 Yagi elements. The grouping of the single Yagis, the system of transmission lines, the phase shifters, the power splitters and the T/R switch are described. Results from the first two campaigns and a survey of future programs demonstrating the flexibility of this mobile system are summarized.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 433-446
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  • 88
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    Design considerations for high-power VHF radar transceivers: Phase matching long coaxial cables using a cable radar (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Poker Flat 49.92-MHz MST radar uses 64 phase-controlled transmitters in individual shelters distributed throughout the antenna array. Phase control is accomplished by sampling the transmitted pulse at the directional coupler of each transmitter and sending the sample pulse back to a phase-control unit. This method requires phase matching 64 long (256 meter) coaxial cables (RG-213) to within several electrical degrees. Tests with a time domain reflectometer showed that attenuation of high frequency components in the long RG-213 cable rounded the leading edge of the reflected pulse so that the cables could only be measured to within 50 cm (about 45 deg at 49.92 MHz). Another measurement technique using a vector voltmeter to compare forward and reflected phase required a directional coupler with unattainable directivity. Several other techniques were also found lacking, primarily because of loss in the long RG-213 cables. At this point it was realized that what was needed was a simple version of the phase-coherent clear-air radar, i.e., a cable radar. The design and operation of this cable are described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 427-428
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  • 89
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    Pulse compression using binary phase codes (1983)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: In most MST applications pulsed radars are peak power limited and have excess average power capacity. Short pulses are required for good range resolution, but the problem of range ambiguity (signals received simultaneously from more than one altitude) sets a minimum limit on the interpulse period (IPP). Pulse compression is a technique which allows more of the transmitter average power capacity to be used without sacrificing range resolution. As the name implies, a pulse of power P and duration T is in a certain sense converted into one of power nP and duration T/n. In the frequency domain, compression involves manipulating the phases of the different frequency components of the pulse. One way to compress a pulse is via phase coding, especially binary phase coding, a technique which is particularly amenable to digital processing techniques. This method, which is used extensively in radar probing of the atmosphere and ionosphere is discussed. Barker codes, complementary and quasi-complementary code sets, and cyclic codes are addressed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 410-414
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  • 90
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    Design considerations of a proposed UK VHF radar (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The major features of a proposed UK VHF radar for meso-, strato-, and tropospheric studies are discussed. The research interests of potential users which were considered in the design analysis are listed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 387-397
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  • 91
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    Outline of the Mu radar (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A middle and upper atmospheric radar system is described. The antenna array consists of 25 groups each of which consists of 19 crossed-Yagis with three elements; each antenna has semiconductor transmitter and receiver, called a module, and each group of 19 antennas works as an independent small radar steering its radar beam under the control of a microcomputer. Thus, the total system consists of 25 small radars of this kind, enabling one to do various sophisticated operations with the system. The system is controlled by two other computers, one for radar controlling (HP9835A) and the other for data taking and on-line analysis (VAX11/750). The computer-controlled system is simple in operation for users and reliable in observation. Very quick beam steering (as quick as in a msec) is also possible because of electronic phase-changing of each module output under control of the microcomputer which is further controlled by the radar controller.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 381-382
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  • 92
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    The Arecibo Observatory as an MST radar (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The radars and other systems at the Arecibo Observatory were designed and built, originally, for incoherent-scatter and radio-astronomy research. More recently, important additions have been made for planetary radar and artificial RF heating of the ionosphere. Although designed and built for a different application, these systems have shown to be very powerful tools for tropospheric, stratospheric and mesospheric research. The Observatory at present has two main radars: one at 430 and the other at 2380 MHz. In addition, 50-MHz MST radar work has been done using portable transmitters brought to the Observatory for this purpose. This capability will become permanent with the recent acquisition of a transmitter at this frequency. Furthermore, control and data processing systems have been developed to use the powerful HF transmitter and antennas of the HF-heating facility as an HF bistatic radar. A brief description of the four radars available at the Observatory is presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 369-374
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  • 93
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    VHF radar measurements during MAP/WINE (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Sensitive Doppler radars which operate in the very high frequency (VHF) band, usually near 50 MHz can measure profiles of background winds, tides, atmospheric gravity waves and turbulence at tropospheric, stratospheric and mesospheric heights. Their ability to observe simultaneously large and small-scale processes makes them unique instruments for studying not only each process separately but also their nonlinear interactions. The mobile VHF radar to be used during the MAP/WINE campaign on Andoya is a modified version of the SOUSY VHF radar being in operation for six years in the Harz Mountains.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 344-345
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  • 94
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    Capabilities and limitations of existing MST radars: Poker Flat (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Designed as a prototype system to continuously monitor the atmosphere up to approximately 100 km, the Poker Flat MST radar began operating in 1979 at a relatively low sensitivity. In almost continuous operation since then, the system is steadily increasing in sensitivity to its ultimate design characteristics. Current and final parameters are listed. The advantages of its modular design, which uses 64 transmitting modules distributed through the 200 mx 200 m antenna array include: easy maintenance, beam switching using very low power switching, air cooled transmitting tubes, lower feedline costs, and no moving parts. Continuous, uninterrupted operation ( 4 years) and less man-made interference because of the remote location) are other assets. Most disadvantages are related to its not-yet-finished status, climate, moose excursions, and operating expenses.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 330-337
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  • 95
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    Characteristics of Sunset radar (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Located in a narrow canyon 15 km west of Boulder, Colorado, the Sunset pulsed Doppler radar was the first radar designed and constructed specifically as a VHF ST radar. The antenna system is a phased array of coaxial-colinear dopoles with computer-controlled phase shifters for each line of dipoles. It operates at a frequency of 40.475 MHz and a wavelength of 7.41M. Peak transmitter power is 100 kW. Aperture efficiency is 0.58 and resistive loss is 0.30 for its 3600 sq m area. The practical steering rate is 1 record/minute/position to any arbitrary antenna beam position. The first clear-air turbulence echoes and wind velocity measurements were obtained in 1974. Significant accomplishments are listed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 320-324
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  • 96
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    The delta S (delta R)-2 question: The pulse-length dependence of signal power for Fresnel scatter (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: It is proposed that the enhanced echoes from the atmosphere observed with a vertically pointing radar are due to reflections from horizontally stratified layers. The general case in which there are many closely spaced layers at random heights is called Fresnel scatter. The variation of received power with transmitter pulse length is examined for various models of Fresnel backscatter. It is shown that for the model most often used in previous work, the power is proportional to the pulse length, and not to the pulse length squared. However, for more general models a more complex pulse length dependence is found.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 124-135
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  • 97
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    Discrimination against interfering signals at the Poker Flat MST radar (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Several on line and off line data processing techniques are used to remove interfering signals due to ground clutter, aircraft, instrumental effects, and external transmissions from the desired atmospheric echoes of Mesosphere Stratosphere, Troposphere (MST) radar. The on line, real time techniques are necessarily simple in order to minimize processing delays. This algorithm examines the individual Doppler spectra which are computed every two to four seconds (for oblique antenna beams). The total spectral power in each individual spectrum is computed by summing all the spectral points. If this integrated power increases from one spectrum to the next by a factor greater than a preselected threshold, then that spectrum is not added to the spectral sum. Succeeding spectra are compared to the last acceptable spectrum. Only a certain maximum number of spectra are allowed to be rejected in succession.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 120-121
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  • 98
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    Interpretation of radar returns from clear air: Discrimination against clutter (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Different kinds of inteference may cause problems to the proper detection and analysis of the atmospheric signals, when using VHF and UHF radars. These are separated into passive and active contributions. Passive contributions are existent in the receiving system without the radar transmitter switched on. Active contributions are due to scatter and reflection of the own transmitted radar signal from unwanted targets, which are called clutter. Of major importance to radar systems are active interference contributions. Different methods can be applied for elimination or at least suppressing unwanted effects. These are; (1) Directional filtering, i.e., applying optimum suppression of antenna sidelobes, (2) Range filtering, i.e., suppressing unwanted signals only in affected range gates, (3) selection by amplitude distributions, (4) Temporal filtering, i.e., recognizing typical temporal variations of the clutter signals, through spectral characteristics, and applying matched filters.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 114-119
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  • 99
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    Effects of pulse width and coding on radar returns from clear air (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: In atmospheric radar studies it is desired to obtain maximum information about the atmosphere and to use efficiently the radar transmitter and processing hardware. Large pulse widths are used to increase the signal to noise ratio since clear air returns are generally weak and maximum height coverage is desired. Yet since good height resolution is equally important, pulse compression techniques such as phase coding are employed to optimize the average power of the transmitter. Considerations in implementing a coding scheme and subsequent effects of an impinging pulse on the atmosphere are investigated.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 98-99
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  • 100
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    On the morphology of the scattering medium as seen by MST/ST radars (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Much is learned about the morphology of the small scale structures of the atmosphere from analysis of echoes observed by MST radars. The use of physical models enables a synthesis of diverse observations. Each model contains an implicit assumption about the nature of the irregularity structure of the medium. A comparison is made between the irregularity structure implicit in several models and what is known about the structure of the medium.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 57-67
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