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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

SAR squint analysis of directional extended targets

Results are presented for multisquint processing of L-band like-polarized (HH) SAR data. Images of agricultural fields were generated by Doppler filtering of SAR signal film, with an angular width and step size of 0.8 deg. The results indicate that field reflectivities may vary by more than 10 dB over a range of less than 1 deg. Implications of observing extremely narrow-beamwidth targets are discussed for platform-pointing and antenna-stability requirements. It is suggested that a multiazimuth Venus-orbiting imaging radar could provide a significant amount of information at a relatively low weight penalty.

Daily, M. I.↗
NASA NTRS1981

Microwave remote sensing measurements of oil pollution on the ocean

Microwave and optical remote sensors were flown over fresh and weathered crude oil released from a surface research vessel and also over a slick formed on the sea by frozen oleyl alcohol cubes released from a helicopter. For the crude oil experiments, microwave radiometric measurements at 1.43, 2.65, 22, and 31 GHz are reported, along with the variable incidence angle scattering measurements at 13.9 GHz. For these experiments, unusual depressions in the L-band brightness temperature were observed, possibly related to dispersants applied to the crude oil. Similar depressions, but with much larger values, were observed over the oleyl alcohol monomolecular slicks. Images obtained at 31 and 22 GHz were used to infer oil volume, yielding values which bound the known amounts spilled. Ku band measurements obtained in repeated passes over crude oil slicks are also discussed.

Croswell, W. F.↗
NASA NTRS1981

Earth resources observation with the Shuttle imaging radar

To fully understand the radar signature of different surface features and covers, observations must be made in a variety of sensor parameters (that is, frequency, polarization, and incidence angle). This makes it possible to choose those sensor parameters that will provide the greatest amount of information about the surface. The Shuttle Imaging Radar (SIR) will be able to obtain surface images at two frequencies (L-band and C-band), at multiple polarizations, and at all incidence angles from near vertical to near grazing. The SIR will operate in the synthetic aperture imaging mode and provide digital images of the surfaces with a resolution of approximately 20 m. As part of the SIR flights, a number of planned large-scale experiments will be carried out in the fields of geologic mapping, vegetation classification, land cover mapping, surface moisture measurements, and ocean surface observation.

Elachi, C.↗
NASA NTRS1982

Use of the Space Shuttle for remote sensing research - Recent results and future prospects

The successful November 1981 test flight of the Space Shuttle Orbiter Columbia has demonstrated the Shuttle's utility and versatility for earth resources-related research. A series of remote sensing experiments is planned for the mid-1980s which will more fully exploit the Shuttle's earth observation capability. The OSTA-1 experiment package of the mission mentioned incorporated the Shuttle Imaging Radar, a synthetic aperture, side-looking device which artificially illuminated the earth's surface with horizontally polarized microwave radiation transmitted at L-band frequency, the Shuttle Multispectral IR Radiometer, which measured the intensity of solar radiation reflected from the earth's surface, the Measurement of Air Pollution from Satellites experiment, which determined the concentration of CO in the earth's atmosphere, the proof-of-concept Feature Identification and Location Experiment, and the Night/Day Optical Survey of Lightning experiment.

Settle, M.↗
NASA NTRS1982

An evaluation of Seasat SAR imagery for urban analysis

Digitally processed Seasat SAR imagery of the Denver, Colorado, area is analyzed with regard to the types of urban data that can be detected and/or inferred from satellite-borne L-band systems. Black-and-white images of the scene were generated at three scales to determine the advantages and detail discernible at each level of display. The large-scale imagery was density-sliced to evaluate the feasibility of producing a semiautomated land-cover classification from the SAR data. Gray level classes were assigned colors to aid interpretation and subsequently compared with the black-and-white images to assess the contribution of each technique and benefits of combining the data from both procedures.

Henderson, F. M.↗
NASA NTRS1982

The effect of monomolecular surface films on the microwave brightness temperature of the sea surface

It is pointed out that monomolecular surface films of biological origin are often encountered on the ocean surface, especially in coastal regions. The thicknesses of the monomolecular films are of the order of 3 x 10 to the -9th m. Huehnerfuss et al. (1978, 1981) have shown that monomolecular surface films damp surface waves quite strongly in the centimeter to decimeter wavelength regime. Other effects caused by films are related to the reduction of the gas exchange at the air-sea interface and the decrease of the wind stress. The present investigation is concerned with experiments which reveal an unexpectedly large response of the microwave brightness temperature to a monomolecular oleyl alcohol slick at 1.43 GHz. Brightness temperature is a function of the complex dielectric constant of thy upper layer of the ocean. During six overflights over an ocean area covered with an artificial monomolecular alcohol film, a large decrease of the brightness temperature at the L-band was measured, while at the S-band almost no decrease was observed.

Alpers, W.↗
NASA NTRS1983

Shuttle Imaging Radar-A information and data availability

The performance characteristics of the Shuttle Imaging Radar (SIR-A), carried aloft on the STS-2 flight, are described and the results of its initial use are evaluated. The SIR-A is an SAR system operated at 1278 MHz (L-band), i.e., a wavelength of 23 cm. A seven panel antenna 9.4 m long was used, and scans were performed at a 50 deg angle of incidence to the center of a 50 km swath. Resolution is 40 m, and imagery is generated on a scale of 1:500,000. Sample images of a Brasilian island and the California coast are provided. Comparisons of the SIR-A imagery with Seasat SAR composite imagery demonstrate that the SIR-A is more sensitive to local roughness and only slightly dependent on terrain slope.

Holmes, A. L.↗
NASA NTRS1983

Improved spatial mapping of rainfall events with spaceborne SAR imagery

The Seasat satellite acquired the first spaceborne synthetic-aperture radar (SAR) images of the earth's surface, in 1978, at a frequency of 1.275 GHz (L-band) in a like-polarization mode at incidence angles of 23 + or - 3 deg. Although this may not be the optimum system configuration for radar remote sensing of soil moisture, interpretation of two Seasat images of Iowa demonstrates the sensitivity of microwave backscatter to soil moisture content. In both scenes, increased image brightness, which represents more radar backscatter, can be related to previous rainfall activity in the two areas. Comparison of these images with ground-based rainfall observations illustrates the increased spatial coverage of the rainfall event that can be obtained from the satellite SAR data. These data can then be color-enhanced by a digital computer to produce aesthetically pleasing output products for the user community.

Ulaby, F. T.↗
NASA NTRS1982

Urban land use classification using synthetic aperture radar

In the cases of such land uses as the commercial and industrial, the incorporation of microwave data to that available from the visible and near visible regions may increase classification accuracy, provided that the limitations inherent in radar data are taken into consideration. Attention is presently given to several approaches to the use of radar data in land use classification of urban and near urban areas, with emphasis on L-band horizontal transmit and horizontal receive data available from Seasat-A. The Los Angeles, CA metropolitan area provides the geographic focus for this study.

Bryan, M. L.↗
NASA NTRS1983

Identification of corn fields using multidate radar data

Airborne C- and L-band radar data acquired over a test site in western kansas were analyzed to determine corn-field identification accuracies obtainable using single-channel, multichannel, and multidate radar data. An automated pattern-recognition procedure was used to classify 144 fields into three categories: corn, pasture land, and bare soil (including wheat stubble and fallow). Corn fields were identified with accuracies ranging from 85 percent for single channel, single-date data to 100 percent for single-channel, multidate data. The effects of radar parameters such as frequency, polarization, and look angle as well as the effects of soil moisture on the classification accuracy are also presented.

Shanmugan, K. S.↗
NASA NTRS1982

Landsat-D, about to be reality

The space and ground segments of the Landsat-D thematic mapper (TM) for remote sensing of a 185 km swath with 30 m resolution are described. Scanning the full earth once every 16 days from its 705 km sunsynchronous orbit, Landsat-D will relay its data on the ku-band through the TDRSS satellite to a ground station. The X-band will also be used to transmit data directly to foreign and domestic ground stations; the S-band will be reserved for MSS data only. Landsat-D comprises the multimission modular spacecraft and the instrument module, which features the MSS and TM, a wideband communication subsystem, a solar array, and an L-band global positioning system. Three computers on the ground provide a high degree of automation for reception, storage, retrieval, back-up, and transmission of data and commands. Additionally, a van is equipped with transportable equipment, including an antenna. Procedures followed for image generation from the MSS and TM are detailed, noting storage at Goddard until dispersal of tapes under the direction of the EROS data center.

Aepli, T. C.↗
NASA NTRS1982

The effects of vegetation cover on the radar and radiometric sensitivity to soil moisture

The measured effects of vegetation canopies on radar and radiometric sensitivity to soil moisture are compared to emission and scattering models. The models are found to predict accurately the measured emission and backscattering for various crop canopies at frequencies between 1.4 and 5.0 GHz, especially at theta equal to or less than 30 deg. Vegetation loss factors, L(theta), increase with frequency and are found to be dependent upon canopy type and water content. In addition, the radiometric power absorption coefficient of a mature corn canopy is 1.75 times that calculated for the radar. Comparison of an L-band radiometer with a C-band radar shows the two systems to be complementary in terms of accurate soil moisture sensing over the extreme range of naturally occurring soil moisture conditions.

Ulaby, F. T.↗
NASA NTRS1983

Radar backscattering properties of corn and soybeans at frequencies of 1.6, 4.75, and 13.3. GHz

The NASA Johnson Space Center made an observational study of the radar-backscattering properties of corn and soybeans in commercial fields in a test site in Webster County, IA. Aircraft-based radar scatterometers measured the backscattering coefficient of the crops at three frequencies, 1.6 GHz (L-band), 4.75 GHz (C-band), and 13.3 GHz (Ku-band), at 10 sensor look-angles (5 to 50 degrees from the nadir in steps of 5 degrees), and with several polarization combinations. Among other findings, it was determined that: (1) row direction differences among fields affected significantly the radar-backscattering coefficient of the fields when the radar system used like-polarization at look-angles from 5 to 25 degrees; (2) row-direction differences had no effect on radar backscattering when the system used either cross-polarization or look-angles greater than 25 degrees regardless of the polarization; (3) wet surface-soil moisture conditions resulted in significantly poorer spectral separability of the two crops as compared to dry-soil conditions; and (4) on the dry-soil date, the best channel for separating corn from soybeans was the C-band cross-polarized measurement at a look-angle of 50 degrees.

Paris, J. F.↗
NASA NTRS1983

Internationally supported data acquisition for solar system exploration in the 1990's

Procedures that could be followed for cooperative agreements between countries with large ground station antennas to help provide mission telemetry support for increasing solar system exploration are outlined. It is noted that mission cost reductions, and thereby greater chances that missions will be approved, are offered by the opportunity to make planetary probes multinational efforts. The Canberra station is a suitable site for the Japanese Planet A Halley's comet intercept probe. The French have requested U.S. cooperation in developing VLBI stations in the L-band to receive signals from the Venus balloons and landers being sent as part of a joint French-Soviet mission to Venus and Halley's comet. The construction of the stations would extend the capabilities already present with NASA's deep space network, particularly for tracking the Voyager visits to Uranus and Neptune.

Reid, M. S.↗
NASA NTRS1983

Microstrip antennas for SAR applications

Current and future microstrip antenna technology development for Spaceborne Synthetic Aperture Radars (SAR) are summarized. Some of the electrical and mechanical characteristics of previously and presently developed microstrip SAR antennas are shown. The SEASAT, the SIR-A and presently the SIR-B antennas are all designed for operation at L-band with approximately 22 MHz of bandwidth. The antennas have linear polarization with minimum of 20 dB of polarization purity. Both the SEASAT and SIR-A antennas were designed for a fixed pointing angle of 20.5 deg and 47 deg, respectively. However, the SIR-B has the added feature of mechanical beam steering in elevation (range). With the exception of different mechanical characteristics, it is concluded that present spaceborne SAR antennas have only single frequency and single polarization performance. The lack of large spaceborne antennas operating at the higher degree of fabrication tolerance required for a given performance; and larger feed and radiating element losses.

Haddad, H. A.↗
NASA NTRS1983

Solid state transmitters for spaceborne radars

The SEASAT-A synthetic aperture radar, the first spaceborne SAR, utilized an all solid state RF signal synthesizer and L-band transmitter to drive a corporately fed flat plate array. The RF signal synthesizer generated a linear FM ""CHIRP'' waveform and provided stable CW reference signals used to upconvert the received signal to a unified S-band downlink channel, and to synchronize satellite control logic. The transmitter generated 1200 watts peak RF power (66 watts average) at a center frequency of 1.275 GHz from 354 watts of DC prime power. Linear FM CHIRP swept symmetrically around the center frequency with a bandwidth of 19.05 MHz and a pulse duration of 33.8 sec. Pulse repetition rate was variable from 1647 to 1944 pps. These transmitter signal parameters combined with the flat plate 34 x 7.5 ft aperture at an orbital altitude of 498 miles and a look angle 20 deg off nadir gave the SAR an 85 foot resolution over a 15.5 mile wide swath.

Turlington, T. R.↗
NASA NTRS1982

Multisensor data analysis and its application to monitoring of cropland, forest, strip mines and cultural targets

Seasat L-band and aircraft X-band dual polarized synthetic aperture (SAR) data of the Western Kentucky Coal Region were examined, preprocessed and combined with Landsat Multispectral Scanner (MSS) data to form a seven-band multisensor data set. Analysis of classified data sets show that the three-band SAR data contain moderate discrimination accuracy for the strip mine class but low accuracy for the residential class. The four-band MSS data contain low classification accuracy for the strip mine and residential classes. The integrated five-band SAR/MSS data show that significant improvement in classification accuracy is obtained for both strip mine and residential classes.

Wu, S. T.↗
NASA NTRS1983

The SIR-B radar on the Shuttle

The Shuttle Imaging Radar-B (SIR-B) will be the third in a series of spaceborne SAR experiments which began with the 1978 launch of Seasat and continued with the 1981 launch of Seasat and continued with the 1981 launch of SIR-A. Like Seasat and SIR-A, SIR-B will operate at L-band and be horizontally polarized. However, SIR-B will allow digitally processed imagery to be acquired at selectable look angles between 15 and 60 deg, thereby permitting for the first time quantitative and analytical studies of the geometric variables associated with a radar image. These geometric variables include look angle and look direction which have never been studied with previous fixed parameter radar systems.

Cimino, J. B.↗