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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The effect of radar azimuth angle on cultural data

Emphasis is placed on the role that the orientation of observed features has on the grey tone of the resulting positive image. As an example it is shown that in the Los Angeles urbanized region, large areas have significantly lower grey tones than adjacent areas having similar land cover. It is determined that this effect is the result of the angle difference between the radar azimuth and the street pattern and especially the orientation of the walls of the structures imaged. Therefore, knowledge of this information is essential in order to ensure accurate interpretation of radar imagery. It is concluded that for radar systems operated from platforms which have fixed azimuth angles (e.g., satellite systems such as Seasat-A), an interpretation methodology, which considers street patterns, is considered especially critical for proper and accurate SAR imagery.

Bryan, M. L.↗
NASA NTRS1979

A 94/183 GHz multichannel radiometer for Convair flights

A multichannel 94/183 GHz radiometer was designed, built, and installed on the NASA Convair 990 research aircraft to take data for hurricane penetration flights, SEASAT-A underflights for measuring rain and water vapor, and Nimbus-G underflights for new sea ice signatures and sea surface temperature data (94 GHz only). The radiometer utilized IF frequencies of 1, 5, and 8.75 GHz about the peak of the atmospheric water vapor absorption line, centered at 183.3 GHz, to gather data needed to determine the shape of the water molecule line. Another portion of the radiometer operated at 94 GHz and obtained data on the sea brightness temperature, sea ice signatures, and on areas of rain near the ocean surface. The radiometer used a multiple lens antenna/temperature calibration technique using 3 lenses and corrugated feed horns at 94 GHz and 183 GHz. Alignment of the feed beams at 94 GHz and 183 GHz was accomplished using a 45 deg oriented reflecting surface which permitted simultaneous viewing of the feeds on alternate cycles of the chopping intervals.

Gagliano, J. A.↗
NASA NTRS1980

Antenna pattern correction procedures for the Scanning Multichannel Microwave Radiometer /SMMR/

Procedures for correcting antenna temperature measurements and retrieving the true brightness temperatures are developed for the Scanning Multichannel Microwave Radiometer (SMMR) flown on the Seasat-A and Nimbus-G satellites. These procedures are necessary to meet the measurement accuracies required for deriving sea surface temperatures and wind speeds. It is shown that sidelobe contributions and polarization cross-coupling are major effects to be accounted for, in addition to some unique features of the SMMR instrument such as integration times and antenna scan characteristics. Methods are presented for data averaging and data reformatting, these are to be used with geophysical parameter retrieval algorithms.

Njoku, E. G.↗
NASA NTRS1980

The SASS scattering coefficient algorithm

This paper describes the algorithms used to convert engineering unit data obtained from the Seasat-A satellite scatterometer (SASS) to radar scattering coefficients and associated supporting parameters. A description is given of the instrument receiver and related processing used by the scatterometer to measure signal power backscattered from the earth's surface. The applicable radar equation used for determining scattering coefficient is derived. Sample results of SASS data processed through current algorithm development facility (ADF) scattering coefficient algorithms are presented which include scattering coefficient values for both water and land surfaces. Scattering coefficient signatures for these two surface types are seen to have distinctly different characteristics. Scattering coefficient measurements of the Amazon rain forest indicate the usefulness of this type of data as a stable calibration reference target.

Bracalente, E. M.↗
NASA NTRS1980

Seasat: - JASIN workshop report. Volume 1: Findings and conclusions

Data acquired from the Joint Air-Sea Interaction (JASIN) Experiment and Seasat data from overpasses that covered the JASIN area were compared and evaluated. The JASIN data were used as a high quality withheld data set. The Seasat data were prepared for each instrument: the Seasat-A Satellite Scatterometer (SASS), the Scanning Multichannel microwave radiometer (SMMR), and the synthetic aperture radar (SAR). The following results demonstrate the performance of Seasat: it was possible to identify mesoscale systems with the SASS as well as fronts; the SMMR provided accurate water vapor content of the atmosphere; the SAR showed evidence of helical rolls in the marine boundary layer; a SASS anomaly could be traced back to thunderstorm activity.

Source record↗
NASA NTRS1980

Digital preprocessing of SEASAT imagery

A model for radar image data is derived for use in developing enhancement techniques. This model describes the image data as the result of a multiplicative-convolved noise process. This information is then used to design a minimum mean square error (MMSE) filter. The resulting filter is implemented adaptively to change with local statistics. A radar image processing technique which provides the MMSE estimate inside homogeneous areas and tends to preserve edge structure is thus developed. This technique has been implemented and tested using digitally correlated SEASAT-A synthetic aperture radar (SAR) imagery.

Frost, V. S.↗
NASA NTRS1981

Flight performance of SEASAT-1 attitude control system

The paper describes the attitude control flight performance of SEASAT-A, (launched in June 1978), until failure of the power subsystem terminated the mission in Oct. 1978. Information provided by the satellite pertained to surface winds and coastal storm activity, currents and wave heights, ocean topography and temperature. The ACS used three-axis momentum exchange and magnetic momentum containment and was set in a nose-down configuration. Attitude control sensing was via horizon sensors and attitude anomalies, resulting from solar interference with the sensors, is covered in detail. Remedial action was taken by reconfiguring the IR scanners, but failure resulted nevertheless. Recommendations for similar future missions include consideration of the effect of light sources and circuit time constants and scan rates. A block diagram of the ACS is included.

Beach, S. W.↗
NASA NTRS1981

Satellite detection of oil on the marine surface

The ability of two widely dissimilar spaceborne imaging sensors to detect surface oil accumulations in the marine environment has been evaluated using broadly different techniques. Digital Landsat multispectral scanner (MSS) data consisting of two visible and two near infrared channels has been processed to enhance contrast between areas of known oil coverage and background clean surface water. These enhanced images have then been compared to surface verification data gathered by aerial reconnaissance during the October 15, 1975, Landsat overpass. A similar evaluation of oil slick imaging potential has been made for digitally enhanced Seasat-A synthetic aperture radar (SAR) data from July 18, 1979. Due to the premature failure of this satellite, however, no concurrent surface verification data were collected. As a substitute, oil slick configuration information has been generated for the comparison using meteorological and oceanographic data. The test site utilized in both studies was the extensive area of natural seepage located off Coal Oil Point, adjacent to the University of California, Santa Barbara.

Wilson, M. J.↗
NASA NTRS1980

Radar image preprocessing

Standard image processing techniques are not applicable to radar images because of the coherent nature of the sensor. Therefore there is a need to develop preprocessing techniques for radar images which will then allow these standard methods to be applied. A random field model for radar image data is developed. This model describes the image data as the result of a multiplicative-convolved process. Standard techniques, those based on additive noise and homomorphic processing are not directly applicable to this class of sensor data. Therefore, a minimum mean square error (MMSE) filter was designed to treat this class of sensor data. The resulting filter was implemented in an adaptive format to account for changes in local statistics and edges. A radar image processing technique which provides the MMSE estimate inside homogeneous areas and tends to preserve edge structure was the result of this study. Digitally correlated Seasat-A synthetic aperture radar (SAR) imagery was used to test the technique.

Frost, V. S.↗
NASA NTRS1981

The study of mesoscale ocean winds

SAR data gathered over the U.S. East Coast are used to infer near-surface wind speed, using a simplified model to relate the strength of the 30 to 40 cm SAR backscatter to surface wind speed. It is found that the SAR backscatter is nearly isotropic with a wind speed exponent of 0.4. Using this exponent, the model is tested against an independent data set. Subsequent agreement between wind speeds simultaneously determined by SAR and the Seasat-A Satellite Scatterometer (SASS) is within 0.7 m/s rms. A one-dimensional Fourier transform of the SAR-derived wind field shows an increasing energy content in rough agreement with the Van der Hoven spectrum.

Jones, W. L.↗
NASA NTRS1981

Seasat data utilization project

During the three months of orbital operations, the satellite returned data from the world's oceans. Dozens of tropical storms, hurricanes and typhoons were observed, and two planned major intensive surface truth experiments were conducted. The utility of the Seasat-A microwave sensors as oceanographic tools was determined. Sensor and geophysical evaluations are discussed, including surface observations, and evaluation summaries of an altimeter, a scatterometer, a scanning multichannel microwave radiometer, a synthetic aperture radar, and a visible and infrared radiometer.

Born, G. H.↗
NASA NTRS1981

Anomalous wind estimates from the Seasat scatterometer

The Seasat-A Satellite Scatterometer (SASS) measured the radar backscatter intensity from the sea surface using a four-beam microwave antenna. Estimates of wind speed and direction derived from these data agree well with surface measurements made during the Joint Air-Sea Interaction experiment, but there are occasions (3 out of 23 satellite passes) when the results are anomalous. One such occasion when the satellite measurements differed substantially from those at the surface of the sea has been studied, and it has been concluded that the interpretation of the SASS measurements may have been vitiated by a mid-level convective system deep enough to produce thunderstorms and lightning.

Guymer, T. H.↗
NASA NTRS1982

Sigma/deg/ signature of the Amazon rain forest obtained from the Seasat scatterometer

Scatterometer data from Seasat of the Amazon rain forest were examined to determine if the region is suitable to use as a reference for calibration of radars. The consistency of Skylab data viewing the Amazon region prompted the analyses, and the Seasat-A scatterometer system (SASS) gathered data of the same region at varying angles. The instrument employed a 100 W 14.6 GHz signal with the reflected power sampled 61 times during each 1.89 sec measurement period. Doppler filters were used in 15 parallel channels of reception, and represented areas 20 km by 50-70 km. Tests were made of regional and temporal stability of the Amazon area, with five measurement angles averaged at different incidence angles to find the mean deviation, which was found to be less than 0.5 dB. Diurnal effects were confined to early morning, and further tests are recommended to obtain results for an entire year, to develop screening methods for thick clouds and rain, and to determine the deviation more precisely.

Birrer, I. J.↗
NASA NTRS1982

SASS measurements of the Ku-band radar signature of the ocean

SeaSat-A Satellite Scatterometer (SASS) measurements of normalized radar cross section (NRCS) have been merged with high quality surface-wind fields based on in situ, to create a large data base of NRCS-wind signature data. These data are compared to the existing NRCS-wind model used by the SASS to infer winds. Falso-color maps of SASS NRCS and ocean winds from multiple orbits show important synoptic trends.

Schroeder, L. C.↗
NASA NTRS1982

The recognition of extended targets - SAR images for level and hilly terrain

Radar image simulation techniques are used to determine the character of SAR images of area-extensive targets, for the cases of flat underlying terrain and of moderate relief, with a view to the severity of elevation change effects on the detection and recognition of boundaries and shapes. The experiment, which demonstrated these effects on shapes and boundaries, was performed in order to establish Seasat-A SAR performance. Attention is given to the geometry/propagation effects in range perspective imaging that must be known for information extraction.

Stiles, J. A.↗
NASA NTRS1982

SASS wind ambiguity removal by direct minimization

An objective analysis procedure is presented which combines Seasat-A satellite scatterometer (SASS) data with other available data on wind speeds by minimizing an objective function of gridded wind speed values. The functions are defined as the loss functions for the SASS velocity data, the forecast, the SASS velocity magnitude data, and conventional wind speed data. Only aliases closest to the analysis were included, and a method for improving the first guess while using a minimization technique and slowly changing the parameters of the problem is introduced. The model is employed to predict the wind field for the North Atlantic on Sept. 10, 1978. Dealiased SASS data is compared with available ship readings, showing good agreement between the SASS dealiased winds and the winds measured at the surface. Expansion of the model to take in low-level cloud measurements, pressure data, and convergence and cloud level data correlations is discussed.

Hoffman, R. N.↗
NASA NTRS1981

A survey of the goals and accomplishments of the Seasat mission

The objectives of the Seasat mission, which was dedicated to establishing the utility of microwave sensors for the remote sensing of the earth's oceans, and data collected during some three months of orbital operations are briefly reviewed. In particular, consideration is given to the Seasat sensors and measurement goals, surface and in situ observations, evaluation organization, and current status of geophysical evaluation for each sensor (altimeter, Seasat-A scatterometer system, scanning multichannel microwave radiometer, visible and infrared radiometer, and synthetic aperture radar). Finally, future plans related to the Seasat project are discussed.

Born, G. H.↗