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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

xsacrcfrspccross (a1)

ARM's scanning cloud radars are fully coherent dual-frequency, dual-polarization Doppler radars mounted on a common scanning pedestal. Each pedestal includes a Ka-band radar (2kW peak power) and the deployment location determines whether the second radar is a W-band (WSACR; 1.7 kW peak power) or X-band (XSACR; 20 kW peak power). At ARM's tropical sites, X-band radars are paired with the Ka-band because they are better suited for the atmospheric attenuation in this region. Beamwidth for the X-band is approximately 1 degree, and the Ka-band beamwidth is roughly 0.3 degrees. Due to the narrow antenna beamwidth, ARM’s scanning cloud radars use scanning strategies unlike typical weather radars. Rather than focusing on plan position indicator, or PPI, scans, the XSACR uses range height indicator, or RHI, scans at numerous azimuths to obtain cloud volume data. For the second ARM Mobile Facility (AMF2), the XSACR can be dismounted from the pedestal it shares with the KASACR and mounted on a separate pedestal. This allows the XSACR to operate more like a weather (precipitation) radar in deployments where such local coverage is lacking. Measurements collected with the XSACR are copolar and cross-polar radar reflectivity, Doppler velocity, spectra width and spectra when not scanning, differential Reflectivity (Zdr), correlation coefficient (rho-hv), and specific differential phase (phi-dp). XSACR data from the 2018–2019 Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign in Argentina are now available as b1-level products. Building on the original CACTI operational data, the b1-level products feature improved data quality resulting from extensive analyses and corrections. The data are cross-calibrated to a common point, datastreams are corrected for operational issues that occurred during the campaign, and several data quality masks and basic derived products are incorporated. For more information, read the CACTI radar b1-level processing report.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

wsacr2cfrcrras (a1)

ARM's scanning cloud radars are fully coherent dual-frequency, dual-polarization Doppler radars mounted on a common scanning pedestal. Each pedestal includes a Ka-band radar (2kW peak power) and the deployment location determines whether the second radar is a W-band (WSACR; 1.7 kW peak power) or X-band (XSACR; 20 kW peak power). Beamwidths at Ka and W bands are roughly matched at 0.3 degrees. Due to the narrow antenna beamwidth, ARM’s scanning cloud radars use scanning strategies that are unlike typical weather radars. Rather than focusing on plan position indicator, or PPI, scans, the Ka-SACR uses range height indicator, or RHI, scans at numerous azimuths to obtain cloud volume data. Measurements collected with the W-SACR are copolar and cross-polar radar reflectivity, Doppler velocity, spectra width and spectra when not scanning, and linear depolarization ration.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

wsacr2cfrvpt (a1)

ARM's scanning cloud radars are fully coherent dual-frequency, dual-polarization Doppler radars mounted on a common scanning pedestal. Each pedestal includes a Ka-band radar (2kW peak power) and the deployment location determines whether the second radar is a W-band (WSACR; 1.7 kW peak power) or X-band (XSACR; 20 kW peak power). Beamwidths at Ka and W bands are roughly matched at 0.3 degrees. Due to the narrow antenna beamwidth, ARM’s scanning cloud radars use scanning strategies that are unlike typical weather radars. Rather than focusing on plan position indicator, or PPI, scans, the Ka-SACR uses range height indicator, or RHI, scans at numerous azimuths to obtain cloud volume data. Measurements collected with the W-SACR are copolar and cross-polar radar reflectivity, Doppler velocity, spectra width and spectra when not scanning, and linear depolarization ration.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

W-Band ARM Scanning Cloud Radar (WSACR) 2nd Generation CF-Radial Spectral Data, Vertically-Pointing Scan, Cross Mode (a1)

ARM's scanning cloud radars are fully coherent dual-frequency, dual-polarization Doppler radars mounted on a common scanning pedestal. Each pedestal includes a Ka-band radar (2kW peak power) and the deployment location determines whether the second radar is a W-band (WSACR; 1.7 kW peak power) or X-band (XSACR; 20 kW peak power). Beamwidths at Ka and W bands are roughly matched at 0.3 degrees. Due to the narrow antenna beamwidth, ARM’s scanning cloud radars use scanning strategies that are unlike typical weather radars. Rather than focusing on plan position indicator, or PPI, scans, the Ka-SACR uses range height indicator, or RHI, scans at numerous azimuths to obtain cloud volume data. Measurements collected with the W-SACR are copolar and cross-polar radar reflectivity, Doppler velocity, spectra width and spectra when not scanning, and linear depolarization ration.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1983

The VPI&SU multiple polarization plane ZDR radar - The OCTOPOD radar

The 'OCTOPOD' radar extends the concept of differential reflectivity (ZDR) to multiple polarization planes, so that ZDR measurements can be made in any pair of orthogonal linear polarizations. This allows the mean canting angle of oblate raindrops or ice particles to be determined. Attention is given to the radar hardware employed, the rotating feed system that generates the multiple polarization planes, and the computer controlled data acquisition system which extracts both reflectivity and ZDR data.

Andrews, J. H.↗
NASA NTRS1986

Observing the polar oceans with spaceborne radar

The application of spaceborne imaging radar data to polar oceanography and sea ice is explored. Several problems come to mind which are presently ripe with ideas and models, but are in need of new data, SAR data, for any progress to be made. These are the study of the ice mass balance, the ice momentum balance, and the circulation of the Arctic Ocean. These problems are described along with the data which is applicable to them and can be extracted from SAR imagery. Some uses are discussed of these data to explore mesoscale processes which affect the oceans and ice cover.

Rothrock, Drew↗
NASA NTRS1993

Imaging radar studies of polar ice

A vugraph format presentation is given. The following topics are discussed: scientific overview, radar data opportunities, sea ice investigations, and ice sheet investigations. The Sea Ice Scientific Objectives are as follows: (1) to estimate globally the surface brine generation, heat flux, and fresh water advection (as ice); (2) to monitor phasing of seasonal melt and freeze events and accurately estimate melt and growth rates; and (3) to develop improved treatment of momentum transfer and ice mechanics in coupled air-sea-ice models.

Carsey, Frank↗
NASA NTRS1992

Mercury radar imaging - Evidence for polar ice

The first unambiguous full-disk radar mapping of Mercury at 3.5-centimeter wavelength, with the Goldstone 70-meter antenna transmitting and 26 antennas of the Very Large Array receiving, has provided evidence for the presence of polar ice. The radar experiments, conducted on 8 and 23 August 1991, were designed to image the half of Mercury not photographed by Mariner 10. The orbital geometry allowed viewing beyond the north pole of Mercury; a highly reflective region was clearly visible on the north pole during both experiments. This polar region has areas in which the circular polarization ratio was 1.0 to 1.4; values less than about 0.1 are typical for terrestrial planets. Such high values of this ratio have hitherto been observed in radar observations only from icy regions of Mars and icy outer planet satellites.

Slade, Martin A.↗
NASA NTRS1987

Rain measurement results derived from a two-polarization frequency-diversity S-band radar at Wallops Island, Virginia

A dual polarization meteorological radar is described. It operates with a slow switch having a cycle time of 0.7 sec and incorporates a frequency diversity technique to achieve independent sampling over short intervals of time. Rain rate measurements derived from the dual polarization radar and low and high resolution rain gages located at a remote site are compared. Average percent differences in rainfall of less than 5 percent and 16 percent are demonstrated when comparing the dual polarization radar measurements with the low and high resolution rain gages, respectively. Striking correlations of the rain rates are present during one rain day. The rain measurement cases examined were limited to only light rain rates (less than 7 mm/hr).

Goldhirsh, Julius↗
NASA NTRS2016

Secondary Crater-Initiated Debris Flow on the Moon

In recent work, radar circular polarization echo properties have been used to identify "secondary" craters without distinctive secondary morphologies. Because of the potential for this method to improve our knowledge of secondary crater population-in particular the effect of secondary populations on crater- derived ages based on small craters-it is important to understand the origin of radar polarization signatures associated with secondary impacts. In this paper, we utilize Lunar Reconnaissance Orbiter Camera photographs to examine the geomorphology of secondary craters with radar circular polarization ratio enhancements. Our investigation reveals evidence of dry debris flow with an impact melt component at such secondary craters. We hypothesize that these debris flows were initiated by the secondary impacts themselves, and that they have entrained blocky material ejected from the secondaries. By transporting this blocky material downrange, we propose that these debris flows (rather than solely ballistic emplacement) are responsible for the tail-like geometries of enhanced radar circular polarization ratio associated with the secondary craters investigated in this work. Evidence of debris flow was observed at both clustered and isolated secondary craters, suggesting that such flow may be a widespread occurrence, with important implications for the mixing of primary and local material in crater rays.

Martin-Wells, K. S.↗
NASA NTRS1992

Enhancement of Thomson scatter by charged aerosols in the polar mesosphere - Measurements with a 1.29-GHz radar

The summer polar mesosphere was observed with the Sondrestrom 1.29-GHz radar with a new high-resolution data acquisition mode. On one occasion, a spatially narrow enhancement in the backscattered power was seen near an altitude of 88 km. Possible explanations are discussed and it is proposed that this layer may be the first example of polar mesosphere summer echoes detected above 1 GHz. Specifically, suggested that these echoes are enhanced Thomson scatter from a layer of charged aerosols, and speculate on the size and charge state.

Cho, John Y. N.↗
NASA NTRS1981

A parametric study of tillage effects on radar backscatter

An experiment was conducted to study the effects of tillage and row spacing on radar backscatter without the variables of moisture and vegetation. To accomplish this objective, a test site was selected in an area characterized by minimal rainfall and sparse vegetation, and simulation rows were plowed on two adjacent 762 x 152.4 m plots, across the 762-m dimension on one plot and along the 762-m dimension on the other plot. It is found that row direction is a significant contributor to radar linearly polarized backscatter from cropland and must be considered when making radar measurements over bare or sparsely vegetated fields. Although the effect decreases with increasing frequency, it is still large (5 dB) at 13.3 13.3 GHz. It is also found that row effects may not exist in cross-polarized radar returns, in which case further measurements with an improved scatterometer system (30-35 dB cross-polarization isolation) are needed.

Fenner, R. G.↗
NASA NTRS1978

Significance of dual polarized long wavelength radar for terrain analysis

Long wavelength systems with improved penetration capability have been considered to have the potential for minimizing the vegetation contribution and enhancing the surface return variations. L-band imagery of the Arkansas geologic test site provides confirmatory evidence of this effect. However, the increased wavelength increases the sensitivity to larger scale structure at relatively small incidence angles. The regularity of agricultural and urban scenes provides large components in the low frequency-large scale portion of the roughness spectrum that are highly sensitive to orientation. The addition of a cross polarized channel is shown to enable the interpreter to distinguish vegetation and orientational perturbations in the surface return.

Macdonald, H. C.↗
NASA NTRS1978

Dual polarized long wavelength radar for discrimination of agricultural land use

The scattered return of imaging radars is primarily sensitive to target structure or roughness and to composition of complex permittivity. The relative degree of penetration, or the depth of material to which the return is sensitive, also varies directly with the wavelength. Where vegetation can be eliminated as a factor, the surface return may be analyzed for variations in roughness or composition (primarily moisture content). L-band (25-cm) imagery has provided evidence that long-wavelength systems with improved penetration capability have the potential for minimizing the vegetation contribution and enhancing the surface return variations. However, the increased wavelength increases the sensitivity to large-scale structure. In the present paper, it is shown that addition of a cross polarized channel enables the interpreter to distinguish vegetation and orientation perturbations in the surface return.

Waite, W. P.↗