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All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Directivity and spacing for the antenna elements

The optimum design choice for the MST radar antenna was considered. The following factors are required: directivity and gain; beam width and its symmetry; sidelobe levels, near and wide angle; impedance matching; feeder network losses; polarization diversity; steerability; cost effectiveness; and maintainability. The directivity and related beam forming aspects of various antenna elements and directivity aspects when such elements are formed into an array are discussed. Array performance for important variables, in particular, the spacing of the elements is considered.

Koshy, V. K.↗
NASA NTRS1985

The SIR-C experiment - Measuring new variables from space with SAR

SIR-C is a continuation of the Shuttle Imaging Radar (SIR) series of synthetic aperture radar (SAR) imaging systems flown by the Jet Propulsion Laboratory aboard the Space Shuttle. SIR-A, flown in 1981, showed that SAR can be a useful remote sensing tool in the fields of geology, hydrology, and oceanography. SIR-B added the capability of moving the radar's antenna in 1984, showing that multiple incidence angle images add materially to the usefulness of SAR. SIR-C will add the dimensions of wavelength and polarization, providing the most powerful system ever flown for SAR scientific studies of the earth.

Wall, S. D.↗
NASA NTRS1987

Multipolarization SAR data for surface feature delineation and forest vegetation characterization

This paper presents the utility of multipolarization Synthetic Aperture Radar (SAR) data for surface feature delineation and forest vegetation characterization. Three channels of radioed data (VV/HH, VH/HH, and VH/VV) are generated from the HH, VV, and VH polarization data (V = vertical, H = horizontal). The radioed data are linearly stretched to yield a digital number within a range of 0 to 255. The techniques for reducing SAR speckle noise and for measuring the degree of separation are discussed. For surface feature delineation, the results indicate that cross polarization as well as cross polarization radioed data better delineate those surface features that are difficult to separate by like polarization data. The results suggest using a median value filtering technique to reduce within-plot data fluctuation to increase the separability measure. For forest vegetation characterization, the results indicate that multipolarization SAR data may be used to estimate forest properties such as total-tree biomass, basal area, and tree height.

Wu, Shih-Tseng↗
NASA NTRS1988

Multifrequency imaging radar polarimetry: Depolarisation of radar echoes at three wavelengths

It is shown that high resolution imaging radar polarimeters can describe depolarization effects in great detail by measuring the complete Stokes matrix for small regions on the Earth's surface, permitting to distinguish between coherent polarization transformation by the surface and diffuse interactions that randomize the polarization state of the received wave. Multiwavelength polarimeter observations of a variety of types of terrain, including images of the coherent and diffuse parts of the received signal are presented. The diffuse image, in particular, is highly indicative of small-scale surface roughness, an effect illustrated by analyzing a set of polarimeter images acquired over lava fields of varying roughness.

Zebker, H. A.↗
NASA NTRS1992

Analysis of volcanic surface morphology on Venus from comparison of Arecibo, Magellan, and terrestrial airborne radar data

The paper compares Arecibo Observatory and Magellan radar data for Venus to airborne radar images for potential terrestrial analog surfaces. Volcanic deposits in western Eistla Regio and northern Sedna Planitia are characterized. It is shown that the expected-sense circularly polarized echoes in the 'dark plains' and broad flow aprons of Eistla Regio decrease rapidly with incidence angle. This angular scattering behavior implies surfaces no rougher than terrestrial pahoehoe flows. Polarization ratio comparisons show that the extensive lava flows in Western Eistla Regio and Sedna Planitia are generally consistent with the properties of terrestrial pahoehoe flows, with only limited occurrences of a'a morphology. Three scenarios are suggested. Many of the large flow units in the two study regions were emplaced as complexes of low-effusion rate pahoehoe flows, rather than as higher eruption rate events which might be expected to produce a'a surface textures; the long lava flows were originally emplaced as a'a but have since weathered to a smoother texture; or a combination of atmospheric and magma compositional effects combine to inhibit a'a formation even at high volume eruption rates.

Campbell, Bruce A.↗
NASA NTRS1992

Relative phase calibration of the NASA/DC-8 three-frequency polarimetric SAR system

Relative phase calibration of radar polarimetry data may be achieved by utilizing the phase information of the receiver calibration tone and knowledge of the antenna path differences among channels measured upon installation of the radar polarimeter. This calibration method does not require any assumptions on the scattering behavior of the scene. This method of phase calibration may be verified by examining the polarization signatures of calibration instruments such as the trihedral corner reflectors.

Lou, Yunling↗
NASA NTRS2003

A Proposed Robotic Astronomy Mission to the Lunar South Polar Regions

This paper outlines a possible mission to emplace a robotic infrared / submillimeter wave interferometer array near the lunar south pole. This region has now been investigated by the Clementine and Lunar Prospector missions, and by Earth-based radar, and its topography and thermal environment are fairly well-known. The area would be exceptionally suitable for infrared / submillimeter astronomy because of the continually low temperatures, approaching that of liquid nitrogen (77K) in some places. A submillimeter spaceborne interferometer mission, Submillimeter Probe of the Evolution of the Cosmic Structure (SPECS) has been proposed by John Mather and others, covering the 40 - 500 micron region with 3 formation flying telescopes. The present paper proposes a lunar adaptation of the SPECS concept, LSPECS. This adaptation would involve landing 4 telescopes on the area north of Shackleton crater at zero degrees longitude. This is in nearly year round darkness but is continually radar visible from Earth. The landed payload of LSPECS would include a telerobotic rover, 4 three meter submm telescopes, a solar power array to be emplaced on the continually sunlit north rim of Shackleton crater, and an S-band antenna for data relay to Earth. Passive cooling without the use of expendable cryogenics. might be possible, trading long exposure time for instrument temperatures above that of liquid helium. The LSPECS would permit long-term study of an extremely wide range of cosmic and solar system phenomena in the southern celestial hemisphere. For complete sky coverage, a similar installation near the north pole would be required. The LSPECS site would also be suitable other types of observation, such as optical interferometry or centimeter wavelength radio astronomy. The lunar south pole is also of great interest because of its extensive ice deposits, which may represent cometary infall with pre-biotic compounds.

Lowman, Paul D., Jr.↗
NASA NTRS2009

Cold Season QPF: Sensitivities to Snow Parameterizations and Comparisons to NASA CloudSat Observations

As operational numerical weather prediction is performed at increasingly finer spatial resolution, precipitation traditionally represented by sub-grid scale parameterization schemes is now being calculated explicitly through the use of single- or multi-moment, bulk water microphysics schemes. As computational resources grow, the real-time application of these schemes is becoming available to a broader audience, ranging from national meteorological centers to their component forecast offices. A need for improved quantitative precipitation forecasts has been highlighted by the United States Weather Research Program, which advised that gains in forecasting skill will draw upon improved simulations of clouds and cloud microphysical processes. Investments in space-borne remote sensing have produced the NASA A-Train of polar orbiting satellites, specially equipped to observe and catalog cloud properties. The NASA CloudSat instrument, a recent addition to the A-Train and the first 94 GHz radar system operated in space, provides a unique opportunity to compare observed cloud profiles to their modeled counterparts. Comparisons are available through the use of a radiative transfer model (QuickBeam), which simulates 94 GHz radar returns based on the microphysics of cloudy model profiles and the prescribed characteristics of their constituent hydrometeor classes. CloudSat observations of snowfall are presented for a case in the central United States, with comparisons made to precipitating clouds as simulated by the Weather Research and Forecasting Model and the Goddard single-moment microphysics scheme. An additional forecast cycle is performed with a temperature-based parameterization of the snow distribution slope parameter, with comparisons to CloudSat observations provided through the QuickBeam simulator.

Molthan, A. L.↗
NASA NTRS1988

Effects of variation in look angle and wavelength in radar images for geologic applications: Implications for SIR-C and Magellan

Implications for SIR-C and Magellan of Seasat, SIR-A/B, and aircraft radar images which show that a variety of geologic targets can have similar backscatter and be indistinguishable under given observing wavelengths and/or look angles are discussed. The SIR-C/X-SAR combination provides three wavelengths, each of which may provide significant information not provided by another, and HH, VV, and one cross polarization each provide different and significant information. For study of unvegetated geological targets in relatively flat terrain, images made at smaller look angles probably provide more information than images from larger look angles. For Magellan, the possible existence of aeolian landforms such as sand dunes or sand sheets on Venus cannot be ruled out simply because they are not seen on radar images. The problem of dissimilar features having identical backscatter must also be considered in the Venusian context, where perhaps lava flows and impact ejecta could have similar high backscatter, or conversely, smooth aeolian materials and smooth volcanic ash (if either exist) could have a similar backscatter.

Blom, R. G.↗
NASA NTRS1993

Radio stimulation and diagnostics of space plasmas

We have investigated the small-scale topside ionospheric plasma structures first observed at Millstone Hill, Massachusetts with the 440 MHz incoherent scatter radar. These small-scale obliquely propagating plasma modes occurring in the vicinity of the midlatitude ionospheric trough, have large radar cross-sections and narrow spectral widths. They have, until recently, been dismissed solely as hard target contamination of the incoherent scatter radar. The geophysical conditions associated with the ionospheric trough, such as the field-aligned current activity and steep plasma density gradients, suggest that these recently discovered small-scale topside ionospheric plasmas may also appear in the auroral and polar ionosphere. In fact, this speculation has been corroborated by the preliminary experiments and data analyses at Tromso, Norway and Sondrestromfjord, Greenland. The primary research results are highlighted. Described in Section 3 are the experiments conducted at Arecibo, Puerto Rico in the past summer for simulating the geophysical conditions of generating these topside ionospheric plasma structures. Recommendation for the future research is finally given. Attached as the appendix of this report are several chapters which present the detailed results of research in the concerned topside ionospheric clutter. Highlights of the research results include: (1) causes of the enhanced radar backscatter (ERB) phenomenon; (2) occurrence of the ERB phenomenon; (3) altitudes of the ERB phenomenon; (4) strength of the ERB returns; (5) range of altitudes of the ERB returns; (6) occurrence frequency of the ERB phenomenon; (7) Doppler effect of the ERB phenomenon; (8) persistency of the ERB; and (9) distinction between ERB phenomenon and space object signatures.

Lee, Min-Chang↗
NASA NTRS1985

Age-dating volcanic and alluvial surfaces with multipolarization data

A false-color multipolarization version of one of the images of Owens Valley area acquired by the JPL Synthetic Aperture Radar (SAR) is given. A geologic map of the alluvial fans there (Gillespie, 1982) is also given for comparison. In general, brightness in the multipolarization images can be seen to be inversely proportional to the age of the surfaces. A more detailed investigation of the relationship between backscatter and age of the surfaces was undertaken with calibrated aircraft SAR data. The quantitative relationship between backscatter coefficient and age for the three polarizations is shown. The straight lines connecting the measured data points imply a steady-state process, although the process or processes leading to this relationship may have operated at rates that varied with climate fluctuations, such as the glacial ages. It is expected that the relationship between radar brightness and age is a consistent one, and that with the wider availability of calibrated radar backscatter data, these relationships can be less well-known areas. The effect of variable such as past climate fluctuations, tectonic disturbance, and rock type must be understood before extension beyond the Mojave Desert region can be attempted.

Farr, T. G.↗
NASA NTRS1986

Mapping diverse vegetation with multichannel radar images

Airborne-SAR, SIR-A, Seasat SAR, and Landsat TM images of the Savannah River Plant, a gently sloping area of South Carolina covered with diverse vegetation, are presented and briefly characterized. Preliminary results indicate that multiple-polarization images constructed from the airborne-SAR data give some indication of forest density and understory growth but do not permit discrimination between evergreen and deciduous forests. Heat-tolerant vegetation growing on sand bars in streams bearing thermal effluents from nuclear reactors on the site is found to have a distinguishing polarization signature.

Ford, J. P.↗
NASA NTRS2012

Bright and Dark Polar Deposits on Mercury: Evidence for Surface Volatiles

Measurements of surface reflectance of permanently shadowed areas near Mercury's north pole reveal regions of anomalously dark and bright deposits at 1064-nanometer wavelength. These reflectance anomalies are concentrated on poleward-facing slopes and are spatially collocated with areas of high radar backscatter postulated to be the result of near-surface water ice. Correlation of observed reflectance with modeled temperatures indicates that the optically bright regions are consistent with surface water ice, whereas dark regions are consistent with a surface layer of complex organic material that likely overlies buried ice and provides thermal insulation. Impacts of comets or volatile-rich asteroids could have provided both dark and bright deposits.

Polar Deposits↗
NASA NTRS1980

The role of satellite altimetry in climate studies

The results of three generations of satellite-borne radar altimetry experiments are summarized. The diverse measurements possible from this instrument are shown to be directly applicable to studies of the importance of the oceans in climate. The radar altimeter has unique value for investigations seeking knowledge of the interconnections between ocean dynamics, heat and momentum transfer across the air-sea interface, sea ice extent, and polar ice sheet thickness.

Parsons, C. L.↗
NASA NTRS1982

FIREX mission requirements document for nonrenewable resources

The proposed mission requirements and a proposed experimental program for satellite synthetic aperture radar (SAR) system named FIREX (Free-Flying Imaging Radar Experiment) for nonrenewable resources is described. The recommended spacecraft minimum SAR system is a C-band imager operating in four modes: (1) low look angle HH-polarized; (2) intermediate look angle, HH-polarized; (3) intermediate look angle, IIV-polarized; and (4) high look angle HH-polarized. This SAR system is complementary to other future spaceborne imagers such as the Thematic Mapper on LANDSAT-D. A near term aircraft SAR based research program is outlined which addresses specific mission design issues such as preferred incidence angles or polarizations for geologic targets of interest.

Dixon, T.↗
NASA NTRS1986

Multiple incidence angle SIR-B experiment over Argentina

The Shuttle Imaging Radar (SIR-B), the second synthetic aperture radar (SAR) to fly aboard a shuttle, was launched on October 5, 1984. One of the primary goals of the SIR-B experiment was to use multiple incidence angle radar images to distinguish different terrain types through the use of their characteristic backscatter curves. This goal was accomplished in several locations including the Chubut Province of southern Argentina. Four descending image acquisitions were collected providing a multiple incidence angle image set. The data were first used to assess stereo-radargrammetric techniques. A digital elevation model was produced using the optimum pair of multiple incidence angle images. This model was then used to determine the local incidence angle of each picture element to generate curves of relative brightness vs. incidence angle. Secondary image products were also generated using the multi-angle data. The results of this work indicate that: (1) various forest species and various structures of a single species may be discriminated using multiple incidence angle radar imagery, and (2) it is essential to consider the variation in backscatter due to a variable incidence angle when analyzing and comparing data collected at varying frequencies and polarizations.

Cimino, Jobea↗
NASA NTRS1990

Satellite radar altimetry over ice. Volume 4: Users' guide for Antarctica elevation data from Seasat

A gridded surface-elevation data set and a geo-referenced data base for the Seasat radar altimeter data over Greenland are described. This is a user guide to accompany the data provided to data centers and other users. The grid points are on a polar stereographic projection with a nominal spacing of 20 km. The gridded elevations are derived from the elevation data in the geo-referenced data base by a weighted fitting of a surface in the neighborhood of each grid point. The gridded elevations are useful for the creating of large-scale contour maps, and the geo-referenced data base is useful for regridding, creating smaller-scale contour maps, and examinating individual elevation measurements in specific geographic areas. Tape formats are described, and a FORTRAN program for reading the data tape is listed and provided on the tape.

Zwally, H. Jay↗