Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “SARS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Features and technologies of ERS-1 (ESA) and X-SAR antennas

Features and technologies of planar waveguide array antennas developed for spaceborne microwave sensors are described. Such antennas are made from carbon fiber reinforced plastic (CFRP) employing special manufacturing and metallization techniques to achieve satisfactory electrical properties. Mechanical design enables deployable antenna structures necessary for satellite applications (e.g., ESA ERS-1). The slotted waveguide concept provides high aperture efficiency, good beamshaping capabilities, and low losses. These CFRP waveguide antennas feature low mass, high accuracy and stiffness, and can be operated within wide temperature ranges.

Schuessler, R.↗
NASA NTRS1986

SAR imaging of bottom topography in the ocean: Results from an improved model

A two-space dimensional model, which is applicable to arbitrary bottom topography and wind, is applied to Seasat Revs. 762, 957, 1430, and 1473. The model includes the additional modulational effects of a long-wave field on the short Bragg waves, both in the presence of a variable current field and results compared to data. Modulations associated with other radar frequencies are also calculated under Rev. 762 conditions. It is shown that when the long-wave field effects are included, signature strength does not decrease with increasing radar frequency. The percentage enhancement due to long waves ranges from 7% for L band to 850% for K band.

Yuen, H. C.↗
NASA NTRS1986

Optimal Doppler centroid estimation for SAR data from a quasi-homogeneous source

This correspondence briefly describes two Doppler centroid estimation (DCE) algorithms, provides a performance summary for these algorithms, and presents the experimental results. These algorithms include that of Li et al. (1985) and a newly developed one that is optimized for quasi-homogeneous sources. The performance enhancement achieved by the optimal DCE algorithm is clearly demonstrated by the experimental results.

Jin, M. Y.↗
NASA NTRS1986

406-MHz geostationary SAR experiment

The ability of a 406-MHz satellite to detect and locate aeronautical, maritime, and terrestrial distress incidents is investigated. The geostationary satellite, uplink and downlink budgets, and processors utilized in the experiment are described. The experiment involves: (1) benchmark testing, (2) verification of spacecraft repeater performance, (3) system evaluation, and (4) environmental testing. The Canadian processor data reveal that the processor threshold is 28 dB Hz, the degradation at 27 dB Hz is significant, the median distress message throughput time is 6 minutes, and the microcomputer can handle 10 distress incidents per hour.

Dumont, P.↗
NASA NTRS1986

A possible SAR arc energization source - Precipitating electrons

Coincident measurements by ground-based photometers and satellite-borne electron sensors have shown the association of precipitating electrons and Stable Auroral Red Arcs at midlatitudes. Modeling of these events has suggested that, within the constraints imposed by uncertainties of the electron energy spectrum, the electron influx carries sufficient energy to establish ionospheric temperatures required to power the arcs.

Slater, D. W.↗
NASA NTRS1988

Locating Spaceborne SAR Imagery

TLOCATE computer program developed to determine precise location of arbitrary picture element in digital synthetic-aperture-radar image. Written in FORTRAN 77.

Curlander, J. C.↗
NASA NTRS1988

Modelling of SAR polarisation phase difference from trees

The data for polarization phase difference Delta Phi between the HH- and VV-polarized backscattered waves from tree-covered fields were obtained with an airborne synthetic aperture radar at 1.225 GHz. The mean values over tree-covered fields were derived from the images of the phase difference and were examined as a function of incident beam angle from 15 to 55 deg. A theoretical model for simulating these data, based on the electromagnetic wave scatterings from the tree trunk and its branches, both of which are assumed as very long dielectric cylinders was developed. The radius and direction of a tree branch are taken as random variables and are chosen by a Monte Carlo method to encounter the incident waves in producing the scattering events. The Monte Carlo simulated results are in good agreement with the observations within experimental uncertainty.

Mo, Tsan↗
NASA NTRS1988

Design considerations for advanced multi-polarisation SAR

System design and verification of an airborne imaging radar (AIR) system are discussed. Issues of importance to multipolarization systems (e.g., mutual coherence and amplitude balance between channels) are emphasized. Methods of detecting and correcting channel imbalances are discussed, and AIR test results are presented.

Klein, J. D.↗
NASA NTRS1988

The NASA/JPL multifrequency, multipolarisation airborne SAR system

Polarimetric synthetic aperture radars, operating at L-, C- and P-band, were designed to replace and upgrade a system destroyed in an aircraft accident. Ground and flight tests were conducted, and the radar was flown over a calibration site in a sequence of experiments designed to calibrate the system. The radar also took part in science campaigns.

Held, D. N.↗
NASA NTRS1988

Concepts for processing and analyzing of multiple SAR and Landsat images

The use and application of multisensor data sets are an absolute necessity for remote sensing to fulfill its promise. Initial efforts at registering dissimilar images have been made, but results are not widely available. This paper describes some initial work to better understand the difficulties of multisensor registration. Accuracies achieved are in excess of a pixel diameter.

Thomas, J.↗
NASA NTRS1989

Radar interpretation of lava fields as a function of incidence angle - Implications for interpretation of Magellan SAR data on Venus

The capability of a single frequency, single polarization radar to distinguish different lava flows solely on the basis of their relative radar backscatter as measured by scatterometer profiles is addressed. It is found that mantled and unmantled flow surfaces can be separated by their radar backscatter and become more distinct with increasing incidence angle. Pristine pahoehoe surfaces have backscatter coefficients distinctly different from older flows at small angles, whereas the most modified pahoehoe units are identifiable at larger incidence angles. At all latitudes on Venus, it should be possible to distinguish the style of volcanism responsible for volcanic plains emplacement.

Theilig, E.↗
NASA NTRS1989

Illumination requirements for orbital SAR - Experience from SIR-B Canadian Shield experiments

Synthetic aperture radar illumination requirements for accurate rendition of geological structure in low-relief regions of uniform radar roughness are considered, along with the effect of illumination azimuth biasing. Results of two Shuttle imaging radar Canadian Shield experiments are discussed with emphasis on look azimuth, look direction, and look angle. It is found out that at least two look azimuths, preferably orthogonal, are essential for adequate rendition of regional structure of the area, while four nearly-orthogonal looks are necessary to compensate for slope orientation. This can be accomplished by orbital design with crossing ground tracks or utilizing a squint mode. Attention is given to the acquisition of coverage from look directions 180 deg apart and to multiple look angles desirable for geological applications.

Lowman, P. D.↗
NASA NTRS1990

Object-oriented feature-tracking algorithms for SAR images of the marginal ice zone

An unsupervised method that chooses and applies the most appropriate tracking algorithm from among different sea-ice tracking algorithms is reported. In contrast to current unsupervised methods, this method chooses and applies an algorithm by partially examining a sequential image pair to draw inferences about what was examined. Based on these inferences the reported method subsequently chooses which algorithm to apply to specific areas of the image pair where that algorithm should work best.

Daida, Jason↗