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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Observations of internal waves in the Gulf of California by SEASAT SAR

Internal waves which are among the most commonly observed oceanic phenomena in the SEASAT SAR imagery are discussed. These waves are associated with the vertical displacements of constant water density surfaces in the ocean. Their amplitudes are maximum at depths where the water density changes most rapidly usually at depths from 50 to 100 m, whereas the horizontal currents associated with these waves are maximum at the sea surface where the resulting oscillatory currents modulate the sea surface roughness and produce the signatures detected by SAR.

Fu, L. L.↗
NASA NTRS1984

Utilization of spaceborne SAR data for mapping

Recent developments in automated processing of digital SEASAT SAR imagery have made feasible the generation of large-scale high-resolution maps. Standard preprocessing of raw data into digital images results in geometrically distorted imagery. Computer algorithms have been developed for unsupervised pixel location, geometric rectification, and mosaicking of multiple-image frames without ground control points. These algorithms utilize knowledge of the spacecraft trajectory data, the imaging geometry, and the coherent properties of the sensor to generate the required processing parameters. This paper discusses the advantages as well as the inherent limitations of this technique, analyzes the associated errors, and presents results using SEASAT SAR imagery. Also discussed are the results of the recent shuttle imaging radar (SIR-A) experiment as well as a follow-on experiment (SIR-B) planned for 1984.

Curlander, J. C.↗
NASA NTRS1984

SAR internal wave signature experiment

Internal wave and surface wave observations by research vessels will be conducted in conjunction with aircraft SAR images. Synthetic Aperture Radar Internal Wave Signature Experiment (SARSEX) provides an opportunity to acquire aircraft and spacecraft SAR imagery of internal waves with appropriate sea truth data. Objectives are to investigate basic mechanisms (both hydrodynamic and electromagnetic) responsible for internal wave signatures and quantitatively test theories and models for predicting internal wave signatures from given ocean and radar parameters.

Winokur, R. S.↗
NASA NTRS1984

SAR image enhancement via post-correlation signal processing

Seventeen interpreters ranked sets of computer-generated radar imagery to assess the value of post-correlation processing on the interpretability of SAR (synthetic aperture radar) imagery. The post-correlation processing evaluated amounts to a nonlinear mapping of the signal exiting a digital correlator and allows full use of signal bandwidth for improving the spatial resolution or for noise reduction. The results indicate that it is reasonable to hypothesize an optimal SAR presentation format for specific applications even though this study was too limited to be specific.

Matthews, N. D.↗
NASA NTRS1983

Spaceborne SAR data for land-cover classification and change detection

Supervised maximum-likelihood classifications of Seasat, SIR-A, and Landsat pixel data demonstrated that SIR-A data provided the most accurate discrimination (72 percent) between five land-cover categories. Spatial averaging of the SAR data improved classification accuracy significantly due to a reduction in both fading and within-field variability. The best multichannel classification accuracy (97.5 percent) was achieved by combining the SIR-A data with two Seasat images (ascending and descending orbits). In addition, semiquantitative analysis of Seasat-A digital data shows that orbital SAR imagery can be successfully used for multitemporal detection of change related to hydrologic and agronomic conditions by using simple machine processing techniques.

Brisco, B.↗
NASA NTRS1983

An improvement in SAR image interpretability provided by post-correlation signal processing

A presentation on the basis of subjective analysis of computer-generated SAR imagery depicts the improvement in interpretability obtained by post-correlation signal processing. A parametric study was conducted to determine the improvement in interpretability obtained by the application of signal weighting functions on the post-processed returns. The results suggest that a marked improvement in interpretability results from symmetrizing the exponential distribution of the fading signal. Preliminary analysis indicates that signal weighting improves the contrast ratio between the mean value of adjacent homogeneous regions in a SAR scene.

Matthews, N. D.↗
NASA NTRS1985

CV-990 L-band SAR: A calibration experiment

Calibrated image data is required by most users of synthetic aperture radar (SAR) data particularly those attempting to classify targets based upon their radar backscatter signature as a function of frequency polarization or incidence angle. In this experiment, the backscatter derived by calibrating the NASA/JPL CV-990 L-band SAR, and the backscatter reported from a pass of the NASA/JSC C-130 scatterometer as the two instruments flew over the same site at different times are compared.

Held, D. N.↗
NASA NTRS1985

Lithologic mapping in a sedimentary environment using multipolarization SAR images

Multipolarization Synthetic Aperture Radar (SAR) data from the NASA/JPL aircraft SAR were used in conjunction with LANDSAT Thematic Mapper (TM), Thermal Infrared Multispectral Scanner (TIMS), and Airborne Imaging Spectrometer (AIS) data as part of a three-year research program to evaluate the utility of remote sensing measurements for analysis of sedimentary basins. The purpose of this research effort is to construct stratigraphic columns, map variations in the lithology, geometry, and structure of sedimentary rocks in the Wind River/Bighorn Basin area, Wyoming, and to integrate remote sensing data with conventional rain models of basin formation and evolution.

Evans, D. L.↗
NASA NTRS1985

Potential applications of multipolarization SAR for pine plantation biomass estimation

This study was conducted as a part of the research tasks under the Radar Land Cover Analysis Program. The Radar Land Cover Analysis objective is, through utilization of multisensor data, to gain a basic understanding of the measurements and data characteristics in the visible-IR-microwave regions of the electromagnetic spectrum associated with specific surface features and cover types. Since the results of analysis of data acquired by Shuttle Imaging Radar (SIR-A) and LANDSAT Thematic Mapper (TM) over the study area were reported (NSTL/ERL Report No. 228, December 1984), this study focused on the analysis and evaluation of the L-band multipolarization airborne SAR data acquired over a southeastern pine forest scene. The data acquisition mission was flown on September 8 and 9, 1983. The HH, HV polarizations and the VV, VH polarizations were used on the first and the second day, respectively. Due to instrumentation difficulties, the digital recorder recorded only the second day's data. Because of this, only the VV and VH polarization data were used in this analysis. However, the HH and HV polarization images were available for visual comparison. It appears that SAR digital numbers correlate with the index of green biomass.

Wu, S. T.↗
NASA NTRS1985

Absolute calibration for SAR systems

Absolute calibration of synthetic aperture radar data is desirable for space and time continuity in earth resource investigations. For this purpose, a calibration signal is used to compare data from a calibration flight, during which precision reflectors are imaged, to data from subsequent SAR flights. The calibration signal duplicates the SAR response from a point source. This signal is amplified and converted by the radar system and processed in precisely the same way as data.

Jackson, P. L.↗
NASA NTRS1985

Extracting sea ice data from satellite SAR imagery

With the prospect operational satellite SAR's by the end of the decade, there is a clear need to develop automated algorithms for the extraction of geophysical data about sea ice from high resolution radar imagery. To this end, techniques were developed for distinguishing ice from open water and for resolving the details of deformation within areas 100 km square imaged by SEASAT SAR. The classification of ice and open water is based on the creation of two bands of lower resolution image data: local average brightness, and the local variance of brightness. In the space of these two variables, ice and open water are separated into two distinct clusters. The deformation is found on a 3.4 km mesh by local cross-correlations of the brightness. Comparison with manually determined deformation shows room for improvement in regions of high deformation by using smaller areas for cross-correlation. Th concentration and deformation data are used together to determine localized regions of the scene where open water is produced or lost.

Fily, M.↗
NASA NTRS1985

The NASA/JPL multipolarization SAR aircraft program

The NASA/JPL aircrft program has been in existence for more than a decade. However, during the past two years, there has been a dramatic increase in the capability and scientific utility of this system as an L-band, 4-polarization synthetic aperture radar (SAR) system has become operational. The system is capable of simultaneously and coherently acquiring four independent complex polarization measurements for every pixel in the image. This capability has been exploited by a number of experimenters to generate several new data types that appear to contain significantly more information than was previously available from single or dual polarized SAR systems. The system will ultimately be capable of estimating the entire complex scattering matrix for every pixel on the ground. Within the next year the system will be extended to C-band so that it will be possible to simultaneously acquire 4-polarization imagery at L-band and C-band. This system will be the prototype for the SIR-C experiment that will have similar capabilities and be flown on the Space Shuttle in 1989.

Held, D. N.↗
NASA NTRS1985

Acousto-optic techniques for real SAR imaging

Recent advancements in the development of the Real Time Acousto-optic SAR Processor are presented. In particular, the technique for introducing the azimuth reference function into the processor via an acousto-optic Bragg cell is discussed. This approach permits the reference function to be stored in electronic memory, thus giving the processor the flexibility needed to adapt rapidly to changes in the radar/target geometry. The architecture is described and results are presented which show the applicability of the technique to both spot-light and strip-map SAR.

Haney, M.↗
NASA NTRS1986

Geological applications of multipolarization SAR data

Spaceborne Synthetic Aperture Radar (SAR) data acquired by SEASAT and the Shuttle Imaging Radar (SIR-A/B) operating at L-band with HH polarization were found to be useful in conjunction with other sensors for lithologic discrimination in arid environments with limited vegetation cover. In order to assess the utility of more advanced sensors for geologic research and define the unique contributions each sensor makes, remote sensing data were collected over the Deadman Butte area of the Wind River Basin, Wyoming. The Wind River Basin is an asymmetric sedimentary basin in central Wyoming created during the early Eocene Laramide orogeny. The stratigraphic section of the Deadman Butte study area, which was measured by Woodward is made up of Paleozoic and Mesozoic marine shales, siltstones, limestones, and sandstones. Sensor systems included LANDSAT 4 Thematic Mapper (TM), Thermal Infrared Multispectral Scanner (TIMS) and the Multipolarization, L-band airborne SAR, a prototype for the next Shuttle Imaging Radar (SIR-C). Sensor parameters are given.

Evans, Diane L.↗
NASA NTRS1986

Operational wave forecasting with spaceborne SAR: Prospects and pitfalls

Measurements collected in the Shuttle Imaging Radar (SIR-B) Extreme Waves Experiment confirm the ability of Synthetic Aperture Radar (SAR) to yield useful estimates of wave directional energy spectra over global scales, at least for shuttle altitudes. However, azimuth fall-off effects tend to become severe for wavelengths shorter than about 100 m in most sea states. Moreover, the azimuth fall-off problem becomes increasingly severe as the platform altitude increases beyond 300 km. The most viable solution to the global wave measurements problem may be a low altitude spacecraft containing a combination of both the SAR and the Radar Ocean Wave Spectrometry (ROWS). Such a combination could have a synergy which yield global spectral estimates superior to those of either instrument singly employed.

Beal, R. C.↗
NASA NTRS1986

RADARSAT high throughput SAR processor development

MacDonald Dettwiler & Associates has been involved with the Canadian Radarsat (RSAT) project for a number of years. This included Phase A definition studies and for the past two years, Phase B ground station design and processor prototyping efforts. The current baseline design for the SAR processing facility (SARDPF) is described along with its requirements and functional decomposition. This forms the context for then discussing the prototype SAR processor and extensions necessary to meet current ground station processing requirements.

George, P.↗
NASA NTRS1986

SIR-C, the next generation spaceborne SAR

SIR-C represents a significant advance in spaceborne SAR system capabilities. The design approach is responsive to the requirements identified by the Science Steering Committee. This multimode feature of the sensor will provide science investigators with new dimensions in acquiring and interpreting scientific data. The flexibility of the SIR-C design will provide a core instrument which will meet the needs of SAR data users into the 1990's and serve as a foundation for ultimate incorporation into the EOS platform.

Caro, E. R.↗
NASA NTRS1986

NASA/JPL aircraft SAR operations for 1984 and 1985

The NASA/JPL aircraft synthetic aperture radar (SAR) was used to conduct major data acquisition expeditions in 1983 through 1985. Substantial improvements to the aircraft SAR were incorporated in 1981 through 1984 resulting in an imaging radar that could simultaneously record all four combinations of linear horizontal and vertical polarization (HH, HV, VH, VV) using computer control of the radar logic, gain setting, and other functions. Data were recorded on high-density digital tapes and processed on a general-purpose computer to produce 10-km square images with 10-m resolution. These digital images yield both the amplitude and phase of the four polarizations. All of the digital images produced so far are archived at the JPL Radar Data Center and are accessible via the Reference Notebook System of that facility. Sites observed in 1984 and 1985 included geological targets in the western United States, as well as agricultural and forestry sites in the Midwest and along the eastern coast. This aircraft radar was destroyed in the CV-990 fire at March Air Force Base on 17 July 1985. It is being rebuilt for flights in l987 and will likely be operated in a mode similar to that described here. The data from 1984 and 1985 as well as those from future expeditions in 1987 and beyond will provide users with a valuable data base for the multifrequency, multipolarization Spaceborne Imaging Radar (SIR-C) scheduled for orbital operations in the early 1990's.

Thompson, T. W.↗