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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Forth system for coherent-scatter radar data acquisition and processing

A real time collection system was developed for the Urbana coherent scatter radar system. The new system, designed for use with a microcomputer, has several advantages over the old system implemented with a minicomputer. The software used to collect the data is described as well as the processing software used to analyze the data. In addition a magnetic tape format for coherent scatter data exchange is given.

Rennier, A. D.↗
NASA NTRS2019

Adaptive Antenna Pattern Notching of Interference in Synthetic Aperture Radar Data Using Digital Beamforming

Radio Frequency Interference (RFI) is a growing problem in Synthetic Aperture Radar (SAR)systems as scientific motivations push the radars to lower frequencies and as more wireless services share the frequency spectrum. New, advanced SAR instruments, such as NASA's EcoSAR, DBSAR and DLR's Tandem-L mission, employ a multichannel architecture capable of Digital Beamforming (DBF). Radars with DBF are capable of notching the antenna pattern in specific directions, which can be utilized to suppress RFI on board or in post-processing. A well-researched beamformer for this purpose is the Minimum Variance Distortionless Response (MVDR) Beamformer. However, the number of interferers that can be removed through notching is limited by the number of receive channels. It is therefore essential to adaptively change the antenna pattern notching throughout the image in time and frequency for the best results with a given number of receive channels. In this paper, we present several methods to achieve this notching by making use of the spatial SAR signal distribution in range time, range frequency, azimuth time and azimuth Doppler that is inherent to the SAR imaging geometry. Because this distribution is time-variable and yet predictable, it can be used to improve the angle of arrival estimation of the RFI and the adaptive notching. The presented methods can be applied to a Digital Beamforming (DBF) SAR signal with multiple channels in elevation and/or in azimuth. Simulations show that the proposed methods increase the ability to notch out-of-swath interference from multiple directions and lessen the impact on in-swath interference. The improvement of the interferometric coherence for a single-pass interferogram acquired by NASA's EcoSAR system (capable of DBF in elevation) is demonstrated. The removal of periodic RFI artifacts is achieved.

RFI↗
NASA NTRS1984

Parametric analysis of synthetic aperture radar data acquired over truck garden vegetation

An airborne X-band SAR acquired multipolarization and multiflight pass SAR images over a truck garden vegetation area. Based on a variety of land cover and row crop direction variations, the vertical (VV) polarization data contain the highest contrast, while cross polarization contains the least. When the radar flight path is parallel to the row direction, both horizontal (HH) and VV polarization data contain very high return which masks out the specific land cover that forms the row structure. Cross polarization data are not that sensitive to row orientation. The inclusion of like and cross polarization data help delineate special surface features (e.g., row crop against non-row-oriented land cover, very-rough-surface against highly row-oriented surface).

Wu, S. T.↗
NASA NTRS1980

Determination of spacecraft attitude using synthetic aperture radar data

A method has been developed for precise sensor platform attitude determination which exploits the availability of synthetic aperture radar (SAR) sensors on future planned NASA earth orbiting spacecraft. Using the ephemeris along with data on planet shape and rotation, the relative motion between sensor and target area and therefore the Doppler frequency shift in the returned echo data is determined. Equations have been developed that relate the Doppler shift to the antenna attitude. The method is tested by comparing attitude predictions from SEASAT SAR digital echo data with available conventionally determined SEASAT attitude information.

Wu, C.↗
NASA NTRS1994

Study of auroral dynamics with combined spacecraft and incoherent scatter radar data

The objectives of this project were to study the coupling between the ionosphere and the magnetosphere, and to understand how this coupling was affected by changes in the solar wind. The data used consisted of satellite measurements coordinated with Sondrestrom incoherent scatter radar observations. We focused our efforts on the study of temporal and spatial changes in the dayside auroral precipitation and electric field.

Thayer, Jeffrey P.↗
NASA NTRS2003

An Automated Cloud-edge Detection Algorithm Using Cloud Physics and Radar Data

An automated cloud edge detection algorithm was developed and extensively tested. The algorithm uses in-situ cloud physics data measured by a research aircraft coupled with ground-based weather radar measurements to determine whether the aircraft is in or out of cloud. Cloud edges are determined when the in/out state changes, subject to a hysteresis constraint. The hysteresis constraint prevents isolated transient cloud puffs or data dropouts from being identified as cloud boundaries. The algorithm was verified by detailed manual examination of the data set in comparison to the results from application of the automated algorithm.

Ward, Jennifer G.↗
DOE OSTI2024

Effective Visualization of Radar Data for Users Impacted by Color Vision Deficiency

Color vision deficiency (CVD) is a decreased ability to discern between particular colors. Eight percent of genetic males and half a percent of genetic females have some form of CVD, with many in the radar community falling into this group. When presenting data on a two-dimensional plane, it is common to use colors to represent values via a colormap. Colormap choice in the radar community is influenced by the ability to highlight scientifically interesting features in data, institutional choices, and domain dominance of legacy colormaps. The problem with these current colormaps is that many do not project well for those with CVD (i.e., green next to red). In working with the CVD community to address this problem, multiple colormaps for moments such as equivalent reflectivity factor and Doppler velocity were created for users with forms of CVD such as deuteranomaly, protanomaly, protanopia, and deuteranopia using Python tools such as colorspacious and viscm. We show how these colormaps can improve interpretability for four cases: a mesoscale convective system, a pyrocumulonimbus storm, a wintertime midlatitude cyclone, and widespread storms with a large bird migration. These new radar equivalent reflectivity factor, Doppler velocity, and polarization colormaps are designed to highlight rain, frozen precipitation, nonmeteorological targets, and velocity-based items, are perceptually uniform, and are visually friendly for those with CVD.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2024

Effective Visualization of Radar Data for Users Impacted By Color Vision Deficiency

Color Vision Deficiency (CVD) is a decreased ability to discern between particular colors. Eight percent of genetic males and half a percent of genetic females have some form of CVD, with many in the radar community falling into this group. When presenting data on a two-dimensional plane, it is common to use colors to represent values via a colormap. Colormap choice in the radar community is influenced by the ability to highlight scientifically interesting features in data, institutional choices, and domain dominance of legacy colormaps. The problem with these current colormaps is that many do not project well for those with CVD (i.e., green next to red). In working with the CVD community to address this problem, multiple colormaps for moments such as equivalent reflectivity factor and Doppler velocity were created for users with forms of CVD such as deuteranomaly, protanomaly, protanopia, and deuteranopia using Python tools such as colorspacious and viscm. We show how these colormaps can improve interpretability for four cases: a mesoscale convective system, a pyrocumulonimbus storm, a wintertime mid-latitude cyclone, and widespread storms with a large bird migration. These new radar equivalent reflectivity factor, Doppler velocity, and polarization colormaps are designed to highlight rain, frozen precipitation, non-meteorological targets, velocity-based items, be perceptually uniform, and visually friendly for those with CVD.

Zachary Sherman↗
NASA NTRS1972

Calibration of radar data from Apollo 16 results, part X

Predictions of surface and near surface blockiness using earth based radar measurements were made. Two polarizations of the radar echoes were measured - polarized and depolarized. Particular attention was given to the depolarized echoes. North Ray and South Ray Craters and a 512-m diameter lunar crater in the Flamsteed Ring were used for the study.

Zisk, S. H.↗
NASA NTRS1990

Tropical Rainfall Measuring Mission (TRMM) project. VII - Techniques for radar data processing

The paper describes algorithms for rain-rate profiling with an airborne or space-borne radar. Some problems involved in the radar measurements from an airborne or space-borne platform are discussed. An outline of a dual-frequency algorithm is described and its performance is confirmed by a computer simulation and an airborne experiment. A single-frequency algorithm is developed by introducing a path-integrated rain rate estimated from an attenuation of surface echoes or from microwave brightness temperature. The computer simulation shows good performance for an airborne or space-borne radar.

Meneghini, Robert↗
NASA NTRS1982

Seasat synthetic-aperture radar data reduction using parallel programmable array processors

This paper presents a digital processing system that produces the Seasat synthetic-aperture radar (SAR) imagery. The system consists of a SEL 32/77 host minicomputer and three AP-120B array processors. The partitioning of the SAR processing functions and the design of software modules is described. The rationale for selecting the parallel array processor architecture and the methodology for developing the parallel processing scheme on this system is described. This system attains a Seasat SAR data reduction speed of 2.5 h per 25-m resolution 4-look and 100 km x 100 km image frame. A preliminary performance evaluation of this parallel processing system and potential future applications for remote sensing data reduction are described.

Wu, C.↗
NASA NTRS1972

Venus - Topography revealed by radar data.

Surface height variations over the entire equatorial region on Venus have been estimated from extended series of measurements of interplanetary radar echo delays. Most notable is a mountainous section of about 3-kilometer peak height located at a longitude of 100 degrees (International Astronomical Union coordinate system). The eastern edge has an average inclination of about 0.5 degrees, which is unusually steep for a large-scale slope on Venus. The resolution of the radar measurements along the surface of Venus varied between about 200 and 400 kilometers with a repeatability in altitude determination generally between 200 and 500 meters. The mean equatorial radius was found to be 6050.0 plus or minus 0.5 kilometers.

Campbell, D. B.↗
NASA NTRS1985

Radio phase characteristics of terrain from multipolarized synthetic aperture radar data

Recent advances in digital data acquisition and signal processing technology permit simultaneous measurement of the complex (amplitude and phase) radar backscatter from several polarization-diverse antennas. While absolute phase mesurements remain to be analyzed in detail. The differential phase of signals polarized parallel and perpendicular to the plane of incidence provide information on the scattering mechanisms that dominate the interaction of the radio waves with the terrain. Analysis of phase backscatter maps from a typical urban area yields a bimodal distribution with the two peaks separated by approximately 180 degrees, highly indicative of a dominant simple geometric one bounce-two bounce mechanism. Some maps of agricultural areas exhibit a similar distribution, however, other agricultural areas yield a distribution that, while still bimodal, consists of two peaks separated by about 110 deg. Still other agricultural areas exhibit a more complex distribution. All of the observed phase shifts appear to be independent of incidence angle from at least 20 deg to 55 deg, therefore the 110 degree shifts are inconsistent with both the geometric model used for the urban area and with common dielectric slab models.

Zebker, H. A.↗