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  • 2015-2019  (1)
  • 1990-1994  (10)
  • 1
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    Conceptual design of a spaceborne radar for rain and cloud sensing (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A conceptual design for a mid-latitude orbiting precipitation and cloud mapping radar is discussed. In this conceptual design the radar utilizes a narrow, dual-frequency beam, electronically scanned antenna to achieve 4-km spatial resolution and 300-km cross-track swath. Vertical resolution of 500 m is achieved by short-pulse transmission. It is expected that such system can measure rain rates up to 100 mm/hr for precipitation at the cloud base, surface precipitation up to 20 mm/hr, and cloud reflectivities as low as -39 dBz. By averaging over 100 independent samples, signal reflectivities can be estimated to better than 20 percent. Other rain and cloud characteristics, such as height, thickness, and cell size, can also be extracted from the data.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: In: Atmospheric propagation and remote sensing; Proceedings of the Meeting, Orlando, FL, Apr. 21-23, 1992 (A93-37102 14-74); p. 363-369.
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  • 2
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    Cassini Titan Radar Mapper (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Cassini Titan Radar Mapper is a multimode radar instrument designed to probe the optically inaccessible surface of Titan, Saturn's largest moon. The instrument is to be included in the payload of the Cassini Saturn Mission, scheduled for launch in 1995. The individual modes of Cassini Radar Mapper will allow topographic mapping and surface imaging at few hundred meters resolution. The requirements that lay behind the design are briefly discussed, and the configuration and capability of the instrument are described. The present limited knowledge of Titan's surface and the measurement requirements imposed on the radar instrument are addressed. Also discussed are the Cassini mission and the projected orbits, which imposed another set of design constraints that led to the multitude of modes and to an unconventional antenna configuration. The antenna configuration and the different radar modes are described.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: IEEE, Proceedings (ISSN 0018-9219); 79; 867-880
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  • 3
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    System Design for a Spaceborne Cloud Rada (1994)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: This paper presents some crucial design parameters and a strawman system design for a nadir-looking, 94-GHz spaceborne cloud profiling radar. This sensor is expected to provide cloud measurements at vertical resolution of 500 m and with a minimum detectable cloud reflectivity of slightly better than -30 dBZ. The radar design is intended to be accommodated by a spacecraft with limited resources. It uses a 2-m antenna and an extended interaction amplifier (EIA) that are readily available in either ground-based and airborne applications. For space application, improvements in the EIA lifetime and space qualification will be required. For various reasons, the spaceborne cloud radar system development is expected to be greatly benefited by the implementation of an aircraft cloud radar instrument.
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  • 4
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    Optimal Estimation of Rain Rate Profiles from Single-Frequency Radar Echoes (1992)
    In:  Other Sources
    Details
    Publication Date: 2018-06-11
    Description: The significant ambiguities inherent in the determination of a particular vertical rain intensity profile from a given time profile of radar echo powers measured by a downward-looking (spaceborne or airborne) radar at a single attenuating frequency are well-documented. Indeed, one already knows that by appropriately varying the parameters of the reflectivity-rain-rate (Z - R) and/or attenuation-rain-rate (k - R) relationships, one can produce several substantially different hypothetical rain rate profiles which would have the same radar power profile. Imposing the additional constraint that the path-averaged rain-rate be a given fixed number does reduce the ambiguities but falls far short of eliminating them. While we now know how to generate as many mutually ambiguous rain-rate profiles from a given profile of received radar reflectivities as we like, there remains to produce a quantitative measure to assess how likely each of these profiles is, what the appropriate 'average' profile should be, and what the 'variance' of these multiple solutions is. Of course, in order to do this, one needs to spell out the stochastic constraints that can allow us to make sense of the words 'average' and 'variance' in a mathematically rigorous way. Such a quantitative approach would be particularly well-suited for such systems as the proposed Precipitation Radar of the Tropical Rainfall Measuring Mission (TRMM). Indeed, one would then be able to use the radar reflectivities measured by the TRMM radar from one particular look in order to estimate the most likely rain-rate profile that would have produced the measurements, as well as the uncertainty in the estimated rain-rates as a function of range. Such an optimal approach is described in this paper.
    Keywords: Meteorology and Climatology
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  • 5
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    SAR Ambiguity Study for the Cassini Radar (1993)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: The Cassini Radar's synthetic aperture radar (SAR) ambiguity analysis is unique with respect to other spaceborne SAR ambiguity analyses owing to the non-orbiting spacecraft trajectory, asymmetric antenna pattern, and burst mode of data collection. By properly varying the pointing, burst mode timing, and radar parameters along the trajectory this study shows that the signal-to-ambiguity ratio of better than 15 dB can be achieved for all images obtained by the Cassini Radar.
    Keywords: Earth Resources and Remote Sensing
    Type: IEEE IGARSS '93 Geoscience and Remote Sensing; Tokyo; Japan
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  • 6
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    Simultaneous Retrieval of Surface and Rain Backscattering Parameters from Spaceborne Radar Measurements (1993)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: The precipitation radar planned for the Tropical Rainfall Measuring Mission (TRMM) will be the first of its kind to measure vertical rainfall distributions from space. The TRMM radar will scan +/- 20 degrees across the nadir track. The range-gated backscattering powers over the entire scan swath will be measured, classified (rain versus no-rain), averaged, and processed to derive the rainfall rates. With this observation scheme, there are two major reasons why it is important to know the rain-perturbed backscattering coefficient of the surface background (tilde over sigma_0)...
    Keywords: Meteorology and Climatology
    Type: American Meteorological Society, 26th Intl. Conf. on Radar Meteorology; Norman, OK; United States
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  • 7
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    Development Status of Cassini Radar For Remote Sensing of Titan (1994)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: Cassini Radar is a multimode rada instrument designed to probe the optically inaccessible surface of Titan, Saturn's largest moon. The individual modes will allow surface imaging, surface emissivity measurements. Recently, the breadboard model of this instrument was built and has undergone a series of functional and perfomance tests. The results obtained from these tests indicate that the instrument design is satisfactory and that the various required performance parameters are suffieciently met.
    Keywords: Earth Resources and Remote Sensing
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  • 8
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    Suppression Of Range Sidelobes In Spaceborne Rain-Mapping Radar (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Adequate suppression of range sidelobes in chirp pulse-compression radar system for spaceborne rain-mapping application demonstrated in operation of aircraft version of system. Radar system operates at center frequency of 13.8 GHz, developed for operation aboard NASA DC-8 aircraft to measure vertical rainfall-rate profiles and rain-cell dimensions. Sidelobes suppressed by at least 55 dB. Technique applied to other frequencies, therefore, useful in other radar systems in which low sidelobes at mid to far range needed.
    Keywords: ELECTRONIC SYSTEMS
    Type: NPO-18515 , NASA Tech Briefs (ISSN 0145-319X); 18; 5; P. 85
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  • 9
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    Spaceborne Radar Would Measure Rain And Clouds (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Report describes conceptual design of spaceborne radar system mapping precipitation and clouds at mid-latitudes to provide data for research on global weather and climate. Radar operates at two frequencies. Lower (35 GHz) provides vertical profiles of rainfall at rates up to 20 mm/h and enables probing of cirrus clouds. Higher (94 GHz) enables detection and quantitative measurements of clouds of all types and provides rain profiles at rates up to 10 mm/h.
    Keywords: ELECTRONIC SYSTEMS
    Type: NPO-18274 , NASA Tech Briefs (ISSN 0145-319X); 16; 7; P. 44
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  • 10
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    Radar Altimetry For Topographical Mapping (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Two altimeter concepts based on spaceborne synthetic-aperture-radar (SAR) proposed to gather global, uniformly sampled, high-resolution, topographical data on land and ice. Wide swath and high pulse rate of SAR makes possible to acquire spatially contiguous data over large areas in reasonable amount of time, and time needed for altimetric processing of SAR data considerably less than that needed to generate topographical maps from stereoscopic photographs. Radar less vulnerable to cloud cover and other weather conditions than optical techniques.
    Keywords: ELECTRONIC SYSTEMS
    Type: NPO-18254 , NASA Tech Briefs (ISSN 0145-319X); 16; 10; P. 37
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