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  • COMMUNICATIONS AND RADAR  (8)
  • EARTH RESOURCES AND REMOTE SENSING  (5)
  • 1
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    Spectral and correlation analysis with applications to middle-atmosphere radars (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The correlation and spectral analysis methods for uniformly sampled stationary random signals, estimation of their spectral moments, and problems arising due to nonstationary are reviewed. Some of these methods are already in routine use in atmospheric radar experiments. Other methods based on the maximum entropy principle and time series models have been used in analyzing data, but are just beginning to receive attention in the analysis of radar signals. These methods are also briefly discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions, Kyoto Middle Atmosphere Program. Handbook for MAP. Volume 30: International School on Atmospheric Radar; p 184-227
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  • 2
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    Criteria and algorithms for spectrum parameterization of MST radar signals (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The power spectra S(f) of MST radar signals contain useful information about the variance of refractivity fluctuations, the mean radial velocity, and the radial velocity variance in the atmosphere. When noise and other contaminating signals are absent, these quantities can be obtained directly from the zeroth, first and second order moments of the spectra. A step-by-step procedure is outlined that can be used effectively to reduce large amounts of MST radar data-averaged periodograms measured in range and time to a parameterized form. The parameters to which a periodogram can be reduced are outlined and the steps in the procedure, that may be followed selectively, to arrive at the final set of reduced parameters are given. Examples of the performance of the procedure are given and its use with other radars are commented on.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program: Handbook for MAP. Vol. 14; p 289-293
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  • 3
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    Interference detection and correction applied to incoherent-scatter radar power spectrum measurement (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A median filter based interference detection and correction technique is evaluated and the method applied to the Arecibo incoherent scatter radar D-region ionospheric power spectrum is discussed. The method can be extended to other kinds of data when the statistics involved in the process are still valid.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions, Middle Atmosphere Program. Handbook for MAP, Vol. 20; 10 p
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  • 4
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    An overview of data acquisition, signal coding and data analysis techniques for MST radars (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: An overview is given of the data acquisition, signal processing, and data analysis techniques that are currently in use with high power MST/ST (mesosphere stratosphere troposphere/stratosphere troposphere) radars. This review supplements the works of Rastogi (1983) and Farley (1984) presented at previous MAP workshops. A general description is given of data acquisition and signal processing operations and they are characterized on the basis of their disparate time scales. Then signal coding, a brief description of frequently used codes, and their limitations are discussed, and finally, several aspects of statistical data processing such as signal statistics, power spectrum and autocovariance analysis, outlier removal techniques are discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions, Middle Atmosphere Program. Handbook for MAP, Vol. 20; 10 p
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  • 5
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    A note on the use of coherent integration in periodogram analysis of MST radar signals (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The effect of coherent integration on the periodogram method to estimate the power spectra of MST radar signals is examined. The spectrum estimate usually is biased, even when care is taken to reduce the aliasing effects. Due to this bias, the signal power for Doppler shifted signals is underestimated by as much as 4 dB. The use of coherent integration in reducing the effect of aliased power line harmonics is pointed out.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 509-512
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  • 6
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    Parametrization of Fresnel returns in middle-atmosphere radar experiments (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Weak reflections from sharp discontinuities in radio refractivity are usually invoked to explain the results of radio propagation experiments. The characteristics of refractivity structures required to produce Fresnel returns are examined and experimental evidence for Fresnel returns in middle-atmosphere radar experiments is reviewed. The consequences of these returns on estimating the turbulence and wind parameters are outlined.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 280-285
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  • 7
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    Data processing techniques used with MST radars: A review (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The data processing methods used in high power radar probing of the middle atmosphere are examined. The radar acts as a spatial filter on the small scale refractivity fluctuations in the medium. The characteristics of the received signals are related to the statistical properties of these fluctuations. A functional outline of the components of a radar system is given. Most computation intensive tasks are carried out by the processor. The processor computes a statistical function of the received signals, simultaneously for a large number of ranges. The slow fading of atmospheric signals is used to reduce the data input rate to the processor by coherent integration. The inherent range resolution of the radar experiments can be improved significant with the use of pseudonoise phase codes to modulate the transmitted pulses and a corresponding decoding operation on the received signals. Commutability of the decoding and coherent integration operations is used to obtain a significant reduction in computations. The limitations of the processors are outlined. At the next level of data reduction, the measured function is parameterized by a few spectral moments that can be related to physical processes in the medium. The problems encountered in estimating the spectral moments in the presence of strong ground clutter, external interference, and noise are discussed. The graphical and statistical analysis of the inferred parameters are outlined. The requirements for special purpose processors for MST radars are discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 477-488
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  • 8
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    On long-wavelength magnetic anomalies over Indian region (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A data set composed of vector magnetic measurements obtained by MAGSAT and very accurate altitude determinations made using Sun sensors and star cameras was used to obtain data for very quiet days over the Indian region at 10 S to 40 N and 60 E to 110 E in an effort to determine the validity of quantitative estimates made from aeromagnetic data obtained by removing the core field. To further account for the external effects, the ring current contributions estimated using both X and Z variations were subtracted from the observed values. Before this, the core contribution was eliminated through a spherical harmonic expansion with terms up to N=13. Analysis of the residual measurements using Fast Fourier techniques indicates that the anomalies contain substantial power for wavelengths of about 1500 kms. Because the ring current effect has a spatial structure of this dimension over India, efforts are being made to exactly eliminate these two interfering effects from the data.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: E83-10135 , NASA-CR-169763 , NAS 1.26:169763
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  • 9
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    Spectral characteristics of the MST radar returns (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The salient features of the spectra of atmospheric returns due to random refractivity fluctuations in the Mesosphere, Stratosphere, Troposphere MST region are reviewed. The nonhomogeneous layered structure of turbulence is often evident as multiple peaks in the spectra. The time evolution of the spectra observed with a fine Doppler resolution provides evidence for thin regions of turbulence associated with gravity waves and shear instabilities. Embedded in these regions are horizontally extended refractivity structures that produce enhanced returns due to specular reflections. It is conceivable that some enhanced returns arise due to anisotropy of small scale refractivity structures. Observed correlations of the strength of the returns with their Doppler spread, wind shears, and winds provide insights into the physical mechanisms that produce turbulence.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 105-111
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  • 10
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    MAGSAT for geomagnetic studies over Indian region (1982)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The major activities of the period are summarized. Data tapes generated on an IBM system were read on DEC-10 system new tapes compatible with DEC-10 system were prepared for data sections of interest. Core and external current contributions were removed from selected passes over the Indian region and the residuals analyzed. Possible equatorial electrojet contributions to the MAGSAT data were studied.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: E82-10296 , NASA-CR-168865 , NAS 1.26:168865 , M-38 , PR-2
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