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Geoscience Electronics, IEEE Transactions on

Issue 4 • Date Oct. 1979

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Displaying Results 1 - 25 of 33
  • [Front cover]

    Page(s): c1
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  • IEEE Geoscience Electronics Society

    Page(s): c2
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  • Table of contents

    Page(s): 101 - 102
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  • Scanning the issue

    Page(s): 103 - 104
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  • Applications of Meteorological Doppler Radar for Weather Surveillance near Air Terminals

    Page(s): 105 - 112
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    Meteorological Doppler radar, heretofore a tool for research, can now be considered for operational applications. One important application is to provide data for air traffic controllers to identify weather that may be hazardous to aircraft in terminal areas. Its use at large commercial airports may be justified both by safety and by savings in fuel and operating costs that should result from more precise definitions of hazardous atmospheric conditions. Five measurement tasks are proposed for an airport Doppler radar. The first two, measurement of radar reflectivity in precipitation systems, and measurement of the vertical profile of horizontal winds, have been shown to be ready for operational implementation. Preliminary evidence shows that two others, identification of shear or turbulence in thunderstorms, and identification of wind shear hazards along approach paths, can provide warning of dangerous wind, but work remains to tie the radar measurements to aircraft hazards. The last suggested use, identification and tracking of wake vortex turbulence, has not yet been demonstrated. An airport Doppler radar can certainly provide some data that will increase flight safety; if it proves capable of all the above, it would be in demand. View full abstract»

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  • Estimation of Spectral Moments for Weather Echoes

    Page(s): 113 - 128
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    Estimators of echo signal power, mean Doppler velocity, and spectrum width are investigated. Maximum likelihood (ML) solutions can improve the estimate variances by an order of magnitude over those by the autocovariance or the Fourier method. However, the required computations are excessive for routine implementations on weather radars. Spectrum power estimation together with two conventional methods of mean Doppler and width estimation are reviewed. Several results previously not available are presented. View full abstract»

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  • A Dual-Channel Microwave Radiometer for Measurement of Precipitable Water Vapor and Liquid

    Page(s): 129 - 136
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    The design and performance of a two-channel ground-based microwave radiometer (20.6 and 31.6 GHz) for measurement of total integrated water vapor and cloud liquid in a vertical column are discussed. Unique features of this instrument are a single antenna producing equal beamwidth for the two frequencies, and incorporation of two stable reference loads in a three-way Dicke switching sequence. The latter allows an automatic gain control (AGC) to be applied in a minicomputer. Linear statistical inversion is used to retrieve the precipitable water vapor and liquid quantities which are provided in real time. The instrument has been in reliable operation, continuously and unattended, at the National Weather Service Forecast Office, Denver, CO, for a six-month period. The radiometrically derived precipitable water vapor compares favorably with that obtained from radiosondes. View full abstract»

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  • Design of a Wind Shear Detection Radar for Airports

    Page(s): 137 - 142
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    Designing a radar to detect hazardous wind shear is treated in two steps. First, a field experiment was conducted to determine the strength of the return signal, and statistical results from this experiment are given. Second, these results are used in design of a clear-air radar for shear detection. The tradeoff between wavelength, transmitted power, and antenna size is shown. A simple display technique using a plan shear indicator is also described. View full abstract»

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  • Radar Measurement of Precipitation-Related Depolarization in Thunderstorms

    Page(s): 142 - 150
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    Observations of thunderstorm regions above 4 km have been made by means of a two-channel polarization diversity radar at 16.5 GHz. There is a brief description of the radar equipment. Computer-generated plots of the radar data show regions of depolarization presumably originating in ice-crystal clouds, and abrupt changes in depolarization induced by lightning strokes. There is a discussion of the physical processes causing the various effects. View full abstract»

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  • Simultaneous Observations of Cloud and Precipitation Particles with Vertically Pointing X-Band and Ka-Band Radars

    Page(s): 151 - 153
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    The backscattered energy received at a radar from a cloud is proportional to several parameters which include peak power, antenna constants, and ¿-4, where ¿ is the radar wavelength. The wavelengths of weather radars vary from centimeters to millimeters. In theory, all such radars should be able to detect both cloud and precipitation particles but, because of practical limitation on antenna size and power output, only the shortest wavelength weather radars are sensitive to the full range of sizes covered by these particles (0.01 mm to over 5 mm in dimensions) which can produce echoes ranging over 160 dB. Simultaneous observations of cloud and precipitation systems with X-band (3-cm wavelength) and Ka-band (0.86-cm wavelength) radars provide the needed realizable dynamic range. Simultaneous measurements of this type are described and are shown to reveal the locations within clouds where precipitation is developing and the growth of precipitation with fall distance, as well as providing continuous measurements of cloud top heights. The inadequacy of X-band radars to measure cloud top heights is demonstrated. View full abstract»

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  • Complementary Code and Digital Filtering for Detection of Weak VHF Radar Signals from the Mesosphere

    Page(s): 154 - 161
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    Measurements of the structure and the dynamics of the middle atmosphere with a fine height resolution have been carried out using the SOUSY-VHF-Radar (SOUSY = SOUnding SYstem), operated by the Max-Planck-Institute for Aeronomy in the Harz mountains in Germany. Since the echoes from the middle atmosphere are coherent within a time scale of the order of a second, the received signals are over-sampled and added coherently for that time period. This integration, which is equivalent to a digital combfiltering, improves the signal-to-noise ratio. It is carried out by a hardware adder. In order to detect echoes from the mesosphere, an increase in the effective radiated power is necessary. By applying a 32-element complementary code to long transmitted pulses, the average power is increased and radar returns from the height range between about 65 and 90 km have been recorded with a height resolution of 300 m. The special hardware and software used is described. Some observational results from mesospheric measurements are presented. View full abstract»

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  • Doppler Radar and Radio Observations of Thunderstorms

    Page(s): 162 - 171
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    Three-dimensional motion fields in a thunderstorm are compared to measurements of the radar reflectivity structure of the storm and to the locations of VHF radiation from electrical discharges, in an attempt to determine the physical conditions which prevailed during the electrically active phase of the storm. The observations were obtained from a network of three Doppler radars and a long-baseline radiation source location system during the 1978 Thunderstorm Research International Program (TRIP 78) at Kennedy Space Center, FL. The analysis shows that two cells developed sequentially on the upshear side of the storm. In the second cell, the updraft velocity between 6- and 7-km altitude (-10 to -15°C) increased rapidly to greater than 20 ms-1; and coincided with a substantial increase in the VHF radiation burst rate. Growth of the updraft was accompanied by the simultaneous development of an upper level downdraft on its upshear side. Reflectivity values in excess of 50 dBZ were observed within the vicinity of the updraft, and have been attributed to graupel or hail that was suspended in the updraft and which grew by riming of supercooled water droplets. Initial source locations for each radiation burst formed an umbrella-like pattern above the high-reflectivity core. We interpret the results to be consistent with an ice-ice electrical charging interaction first investigated by Reynolds et al. View full abstract»

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  • A Video Recorder for Coherent Doppler Radar

    Page(s): 171 - 178
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    A system for recording coherent pulse Doppler radar signals on an inexpensive video tape recorder is described. A recording processor translates the radar receiver IF output to a center frequency of 1 MHz. To this is added an amplitude modulated 200-kHz pilot carrier. This unique pilot carrier provides a coherent reference for synchronous demodulation, a timing reference, and synchronization signals for the video tape recorder. A reproducing processor reconstructs the original radar signals from the information contained in the reproduced tape through the use of a pilot tracking loop, which recovers the synchronous reference in the presence of added noise and tape recorder flutter. An analysis of system performance characteristics is included. Of note is the good definition of the start time of the radar interval. Maximum timing jitter at the end of the 1-ms radar interval is about 400-ns peak, and is under 10 ns for the first 10 ¿s of the interval. The linear dynamic range of 27 dB can be used to provide about 4-dB resolution over a 90-dB dynamic range using a log compression technique to be discussed. Comparisons between radar signals measured directly and signals recorded on the radar video recorder indicate that velocity information present in a coherent Doppler radar is preserved with high accuracy. View full abstract»

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  • A Metric Wave Radio-Acoustic Tropospheric Sounder

    Page(s): 179 - 181
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    A metric wavelength version of the radio-acoustic sounding system (RASS) at Trino Vercellese, near Turin, Italy, is presented. Evidence is shown of satisfactory soundings in conditions of calm or light winds. View full abstract»

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  • High-Resolution VHF Radar Sounding of the Troposphere and Stratosphere

    Page(s): 182 - 189
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    Measurements of the fine structure of tropospheric and stratospheric refractivity variations with a vertically beamed pulsed VHF radar are presented. The scheme of radar operation and data acquisition by means of coherent detection and preintegration is described. Special emphasis is placed upon the evaluation of the fine structure through the application of pulse scanning, filtering, and signal deconvolution by means of contrast enhancement. These techniques yield a height resolution of about 30 m in the troposphere. Laminae or thin sheets of refractivity changes are regularly found in the troposphere and lower stratosphere. A cat's eye turbulence structure of 100-m thickness, observed at 4.4-km height, is described in detail. It is concluded from the evaluation of the correlation function that scattering from turbulent refractivity fluctuations occurs in the middle of this layer whereas partial reflection from refractivity gradients dominates at the layer boundaries. Several mechanisms, such as the Kelvin-Helmholtz instability, wave-induced shear generation, or lateral convection, are discussed as possible origin of the refractivity structures revealed by VHF radar. View full abstract»

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  • Polarization and Dual-Wavelength Radar Observations of the Bright Band

    Page(s): 190 - 195
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    Polarization and dual-wavelength radar data are presented for two days on which a radar bright band was observed. The polarization parameters (reflectivity, Circular Depolarization Ratio, and the phase correlation between the main and orthogonal components) are found to yield interpretations about the hydrometeors that are consistent with those obtained from the ratio of the 10- and 5-cm reflectivity factors. Data from stratiform precipitation suggest that wet non-Rayleigh scatterers are present in the vicinity of the 0°C level and in the bright band. The combination of both polarization and dual-wavelength techniques is proven to be more powerful than either technique on its own for the determination of hydrometeor type and size. View full abstract»

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  • A Broad-Band Noise Technique for Fast-Scanning Radar Observations of Clouds and Clutter Targets

    Page(s): 196 - 204
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    This paper describes a relatively simple technique for suppressing interference fluctuations from precipitation and other cluttertype targets. The technique utilizes noise as a transmitted signal and receives the returns in a simple radiometer-type receiver. For noise of bandwidth B and an averaging time equal to transmitted pulselength T, the root-mean-square (rms) fluctuation in the return from a given volume in range is a fraction, ¿¿/¿BT of the mean return, down from a fractional value of unity for unaveraged single-frequency returns. Using this technique, a fast-scanning radar has been constructed which scans the hemisphere overhead every 20 s with a 2.2° beam. For this system, B = 30-40 MHz and T = 1 ¿s, and the error in the reflectivity estimate per transmitted pulse is ¿1-dB rms. Observations of precipitation returns using 300-MHz bandwidth noise are compared to simultaneous single-frequency observations to demonstrate the clutter reducing ability of the noise technique. For 300-MHz bandwidth noise transmissions and an averaging time of 1 ¿s, interference fluctuations are reduced by 25 dB from the single-frequency case, and the mean reflected signal is determined to within 0.3-dB rms in a single transmitted pulse. View full abstract»

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  • Comparison of Remote Measurements by Single- and Dual-Wavelength Meteorological Radars

    Page(s): 205 - 218
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    Dual-wavelength radar was used routinely to observe and record, in digital form, severe convective storms in northeastern Colorado in 1972-1974. By postprocessing, the precipitation-caused attenuation of the attenuating wavelength of the dual-wavelength pair is determined while the other wavelength remains essentially unattenuated. Precipitation rate computed from this attenuation is more accurate than that computed from the radar reflectivity factor Z, the quantity popularly associated with meteorological measurements of storms. The attenuation-derived precipitation over an artificial catchment shows the greatest improvement over that derived from Z at the highest precipitation rates. The attenuation technique has particular strength in that it discounts regions of hail that occur in the heaviest storms which greatly perturb the simple radar reflectivity estimates. The hail signal H is the ratio (expressed in decibels) of the S-band and X-band normalized echo powers from a point in a storm less the attenuation. Using the assumption of spherical hail with exponential size spectra randomly truncated at the upper limit, the equation D0 = 0.31 + 0.12H is a reasonable relationship between this hail signal and the median volume diameter, in centimeters, of the hail. Theoretical relationships relating the hail mass deposition rate and the vertical hail energy flux density are derived and are shown to be correlated with hail totals over the artificial catchment with correlation coefficients exceeding 0.8 for mass and 0.65 for energy. View full abstract»

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  • A Review on the Application of Nonattenuating Frequency Radars for Estimating Rain Attenuation and Space-Diversity Performance

    Page(s): 218 - 239
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    Cumulative rain fade statistics are used by space communications engineers to establish transmitter power and receiver sensitivities for systems operating under various geometries, climates, and radio frequencies. Space-diversity performance criteria are also of interest. This work represents a review, in which are examined the many elements involved in the employment of single nonattenuating frequency radars for arriving at the desired information. The elements examined include radar techniques and requirements, phenomenological assumptions, path attenuation formulations and procedures, as well as error budgeting and calibration analysis. Included are the pertinent results of previous investigators who have used radar for rain-attenuation modeling. Suggestions are made for improving present methods. View full abstract»

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  • Differential Reflectivity Measurements in Rain: First Experiments

    Page(s): 240 - 244
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    Results of the first measurements of differential reflectivity (ZDR) in rain are reported. ZDR = 10 log (ZH/ZV) dB involves copolar measurements of ZH and ZV, the radar reflectivity factors at horizontal and vertical polarizations, respectively. The data were obtained with the University of Chicago-Illinois State Water Survey (CHILL) radar facility in Oklahoma during Spring 1977 and confirmed theoretical expectations that ZDR should be positive, ranging between around 0-4 dB. By combining ZDR measurements with ZH, it is shown how estimates of N0 and D0, the parameters of an exponential raindrop size distribution, can be obtained. These estimates were subsequently used to compute rainfall rates as a function of range along a radar ray. These results illustrate that ZDR can have important applications in the quantitative, remote measurement of drop-size distributions and rainfall. View full abstract»

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  • A Model for the Microwave Emissivity of the Ocean's Surface as a Function of Wind Speed

    Page(s): 244 - 249
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    A quantitative model is presented, which describes the ocean surface as an ensemble of flat facets with a normal distribution of slopes. The variance of the slope distribution is linearly related to frequency up to 35 GHz and constant at higher frequencies. These facets are partially covered with an absorbing nonpolarized foam layer. Experimental evidence is presented for this model. View full abstract»

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  • Automatic Cell Detection and Tracking

    Page(s): 250 - 262
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    Algorithms for the automatic detection and tracking of precipitation cells have been developed for the processing of digital weather radar data. The basic premise of the processing procedure is to represent the essential information in the weather radar data with a significantly smaller data set that describes the characteristics of the radar echo cells and their surrounding echo regions. Radar echo cells are defined by contours 3 dB below enclosed reflectivity peaks which do not enclose other cells. Attributes such as reflectivity, area, and location are tallied for each detected cell. Similar attributes are also tallied for the larger echo regions enclosed by preselected reflectivity value contours that encompass the cells. The attributes are used to extablish and maintain cell tracks within a tilt scan sequence and from one scan sequence to the next. Detected cells persist and produce tracks which last an average of 15 min. The detected cells are relatively small, typically 3 km in diameter, and often occur in clusters. The automatic detection and tracking programs provide a new tool for the analysis of large volumes of weather radar data. View full abstract»

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  • Atmospheric Measurements by VHF Pulsed Doppler Radar

    Page(s): 262 - 280
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    In the past decade the technique of using sensitive Doppler radars to measure wind, turbulence, and stability in the free atmosphere has been developed. Because this technique can be used to study the atmosphere at all heights from near the ground up to about 100 km, it has been named the MST (mesosphere-stratosphere-troposphere) radar technique. Radars that are sensitive enough to make measurements in all three regions are called MST radars; those that can observe only in the troposphere and lower stratosphere are called ST radars. All MST and some ST radars operate in the VHF (30-300-MHz) frequency band. The history, design, measurement capability, and meteorological applications of the VHF MST radar technique are reviewed in this paper. The radar echoes come from refractive index structures in the air that have length scales of the order of half the radar wavelength, 3-4 m for VHF radars in use. The refractive index structures are primarily of two kinds: turbulent and laminar. The former results in turbulent scatter of the radar signal and the latter results in Fresnel (or partial) reflection. Meteorological applications include 1) measurement of wind profiles, particularly for the study of mesoscale phenomena such as gravity waves, fronts, jet steams, tides, wind variability, etc. These applications take advantage of the fact that wind profiles can be measured much more frequently with the MST radar technique than with other techniques. A frequency of about one profile per minute is typical. 2) Measurement of vertical winds. View full abstract»

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  • The RONSARD Radars: A Versatile C-Band Dual Doppler Facility

    Page(s): 281 - 288
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    In this paper, the authors describe a system of two Doppler radars (the RONSARD system) operated for the study of precipitating clouds (fronts and convective storms). In a first part, emphasis is placed on the system requirements concerning both transportability and flexibility, due to the wide range of atmosphere phenomena to be observed. These requirements lead to an original implementation of the aerial, to a special design of the receiving chain (dual-polarization capability, wide dynamic range, absolute selfcalibration capability) and to the implementation of real-time digital subsystems (amplitude and phase memory, ground clutter cancellor, Fourier transform processor, ambiguous velocity corrector, and a spectrum moment computer). The second part is devoted to a brief review of the scientific programs involving the RONSARD system and to the presentation of some preliminary results. View full abstract»

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  • The RONSARD Radars: Internal Calibration Techniques Using Coherent and Noise Sources

    Page(s): 288 - 295
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    The methods for calibrating each meteorological radar of the RONSARD system are described in this paper. The special procedures used have their origin in the complexity of the equipment. The internal calibration of the receiver chain, which is the first step of the overall radar calibration, is described first. The complex structure of the receiver is analyzed and each element replaced by an equivalent circuit, thus yielding a reduced block diagram of the receiver chain. This diagram is then used to determine the receiver gain as a function of the receiver parameters. Special attention is given to the behavior of the receiver adapted filter (preintegrator) and to that of the hard-wired Fourier transformer when processing various types of signal spectra. Three measurements of the receiver gain are finally carried out using calibrated sources (coherent RF source, 10 600 K noise source, and internal radar noise). The results exhibit a correct stability of the radar constant obtained from independent measurements. The addition of quantization noise in the Fourier transformer is also analyzed and discussed. View full abstract»

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Aims & Scope

This Transactions ceased production in 1979. The current retitled publication is IEEE Transactions on Geoscience and Remote Sensing.

Full Aims & Scope