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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The observation of ocean surface phenomena using imagery from the Seasat synthetic aperture radar - An assessment

The principles governing synthetic aperture radar (SAR) and its use on the Seasat spacecraft are reviewed. The way in which wind stress, surface currents, long gravity waves, and surface films modulate the scattering properties of resonant (approximately 30-cm-wavelength) waves is discussed, with particular emphasis placed on the mechanisms that could produce images of long gravity waves. Doppler effects by ocean motion are also described. Measurements of long (wavelength more than about 100 m) gravity waves made using Seasat SAR imagery are compared with surface measurements during several experiments. Combining these results, it is found that dominant wavelength and direction are measured by Seasat SAR within + or - 12% and + or - 15 deg, respectively. It is noted, however, that ocean waves are not always visible in SAR images, and detection criteria are discussed in terms of wave height, length, and direction.

Vesecky, J. F.↗
NASA NTRS1982

Photogrammetry of the Viking Lander imagery

The problem of photogrammetric mapping which uses Viking Lander photography as its basis is solved in two ways: (1) by converting the azimuth and elevation scanning imagery to the equivalent of a frame picture, using computerized rectification; and (2) by interfacing a high-speed, general-purpose computer to the analytical plotter employed, so that all correction computations can be performed in real time during the model-orientation and map-compilation process. Both the efficiency of the Viking Lander cameras and the validity of the rectification method have been established by a series of pre-mission tests which compared the accuracy of terrestrial maps compiled by this method with maps made from aerial photographs. In addition, 1:10-scale topographic maps of Viking Lander sites 1 and 2 having a contour interval of 1.0 cm have been made to test the rectification method.

Wu, S. S. C.↗
NASA NTRS1982

Automatic classification of clouds on Meteosat imagery - Application to high-level clouds

A statistical classification method based on clustering on three-dimensional histograms is applied to the three channels of the Meteosat imagery. The results of this classification are studied for different cloud cover cases over tropical regions. For high-level cloud classes, it is shown that the bidimensional IR-water vapor histogram allows one to deduce the cloud top temperature even for semi-transparent clouds.

Desbois, M.↗
NASA NTRS1980

Interpretation of surface-water circulation, Aransas Pass, Texas, using Landsat imagery

The development of plumes of turbid surface water in the vicinity of Aransas Pass, Texas has been analyzed using Landsat imagery. The shape and extent of plumes present in the Gulf of Mexico is dependent on the wind regime and astronomical tide prior to and at the time of satellite overpass. The best developed plumes are evident when brisk northerly winds resuspend bay-bottom muds and flow through Aransas Pass is increased by wind stress. Seaward diversion of nearshore waters by the inlet jetties was also observed. A knowledge of surface-water circulation through Aransas Pass under various wind conditions is potentially valuable for monitoring suspended and surface pollutants

Finley, R. J.↗
NASA NTRS1982

Determination of surface albedos and aerosol extinction characteristics from satellite imagery

A procedure is developed for calculating atmospheric extinction characteristics (optical thickness, scattering height, single scattering albedo) and surface albedo from radiometric images made at satellite altitudes. The procedure - a fast, computerized method - is suitable for the high-volume processing of satellite imagery data and thus can be used to map temporal and spatial distributions of aerosol parameters. Based on an analytical approximate solution to the equation of radiative transfer in a plane parallel atmosphere, the procedure is primarily applicable to the 0.4-micron to 0.8-micron wavelength range for solar zenith angles from 10 deg to 60 deg, surface albedos between 0.03 and about 0.5, and atmospheric optical thicknesses from 0.2 to 2. With a step-like change in the surface albedo (for example, a seashore or river bank or other similar change of terrain), both surface reflectivity and atmospheric optical thickness can be derived from radiance measurements. In this case, the resultant optical thickness is not based on a known surface reflectivity and is in essence independent of the radiometer calibration.

Kaufman, Y. J.↗
NASA NTRS1982

Location of spaceborne SAR imagery

A method has been developed to determine the location of a pixel in a digital SAR image. This technique utilizes the spacecraft ephemeris data and the characteristics of the SAR data collection system to produce an estimate of the latitude and longitude of an arbitary pixel. This approach has an advantage over previous techniques in that it requires no reference points and is independent of spacecraft attitude knowledge or control. Tests were conducted using Seasat SAR imagery, comparing predicted feature location with the location as determined by high precision area maps. Rusults indicate an accuracy of 200 m is attainable with this method. Error sources are analyzed and recommendations are given to improve image location accuracy in future spaceborne SAR's.

Curlander, J. C.↗
NASA NTRS1982

Familiarization with LANDSAT imagery

Learning objectives of the activities provided include: (1) reading the annotation of a LANDSAT image; (2) becoming acquainted with the characteristics of 1:1,000,000 scale transparencies and prints of MSS images; (3) noting the general information visible in LANDSAT photo products; (4) observing changes of appearance of any ground feature or class in the black and white images made from the four MSS bands and the characteristic color of each class in color composites; (5) determining the degree to which a LANDSAT image meets map accuracy standards and can be fitted to map projections; (6) assessing the effects of LANDSAT enlargements and scale changes and of the limitations of satellite resolution relative to aerial photos; (7) observing the influence of time of acquisition (season) on a scene; (8) getting a feel for image quality as dependent on processing and photoreproduction; (9) appreciating the characteristics of the RBV and thermal band imagery obtained from LANDSAT-3; and (10) becoming familiar with certain attributes of adjacent LANDSAT images which permit them to be joined in mosaics and to be viewed in stereo.

Source record↗
NASA NTRS1981

Diazo processing of LANDSAT imagery: A low-cost instructional technique

Diazo processing of LANDSAT imagery is a relatively simple and cost effective method of producing enhanced renditions of the visual LANDSAT products. This technique is capable of producing a variety of image enhancements which have value in a teaching laboratory environment. Additionally, with the appropriate equipment, applications research which relys on accurate and repeatable results is possible. Exposure and development equipment options, diazo materials, and enhancement routines are discussed.

Lusch, D. P.↗
NASA NTRS1981

Area estimation of forestlands in southwestern Michigan from LANDSAT imagery

The accuracy of mapping and estimating the area of forestlands in southwestern Michigan from winter and fall LANDSAT images was evaluated. All omission and commission errors in the LANDSAT forest maps were identified and mapped through comparison with an existing detailed forest cover type map. Accuracies ranged from 74.0% to 98.5% and were higher for the winter imagery. Most errors (85%) occurred along the perimeter of forestlands and were less than 4 hectares (10 acres) and size. Other factors affecting interpretation are reported as well as time and image availability considerations.

Karteris, M. A.↗
NASA NTRS1982

Vertical eddy diffusion coefficient from the LANDSAT imagery

Analysis of five stable cases of the smoke plumes that originated in eastern Cabo Frio (22 deg 59'S; 42 deg 02'W), Brazil using LANDSAT imagery is presented for different months and years. From these images the lateral standard deviation (sigma sub y) and the lateral eddy diffusion coefficient (K sub y) are obtained from the formula based on Taylor's theory of diffusion by continuous moment. The rate of kinetic energy dissipation (e) is evaluated from the diffusion parameters sigma sub y and K sub y. Then, the vertical diffusion coefficient (K sub z) is estimated using Weinstock's formulation. These results agree well with the previous experimental values obtained over water surfaces by various workers. Values of e and K sub z show the weaker mixing processes in the marine stable boundary layer. The data sample is apparently to small to include representative active turbulent regions because such regions are so intermittent in time and in space. These results form a data base for use in the development and validation of mesoscale atmospheric diffusion models.

Viswanadham, Y.↗
NASA NTRS1981

The estimation of convective precipitation from GOES imagery with the Griffith/Woodley technique

Improved rainfall monitoring using satellite and conventional data are described. A method was developed to: (1) provide rainfall evaluations more uniform, accurate and complete than can be derived from satellite or conventional data alone; (2) serve current operational environmental program in countries with special needs for improved rainfall data; (3) invoke either polar orbiting and/or geostationary imagery as the satellite inputs; (4) utilize global telecommunication system (GTS) SYNOP messages as the basic conventional data inputs; (5) be applicable to any and all types of weather situations in the operational areas; (6) be undemanding in hardware and software so as to be an option available for use even by nations or agencies with very limited financial resources.

Griffith, C. G.↗
NASA NTRS1980

Monitoring land degradation in southern Tunisia: A test of LANDSAT imagery and digital data

The possible use of LANDSAT imagery and digital data for monitoring desertification indicators in Tunisia was studied. Field data were sampled in Tunisia for estimation of mapping accuracy in maps generated through interpretation of LANDSAT false color composites and processing of LANDSAT computer compatible tapes respectively. Temporal change studies were carried out through geometric registration of computer classified windows from 1972 to classified data from 1979. Indications on land degradation were noted in some areas. No important differences, concerning results, between the interpretation approach and the computer processing approach were found.

Hellden, U.↗
NASA NTRS1981

Analysis of Jamaican lineaments visible in Seasat-SAR imagery

Three digitally correlated Seasat SAR frames of Jamaica are used to examine the fault-related topography of the island. The major fault-controlled lineaments visible in the imagery are described, and some generalizations are made with respect to the recent tectonics of Jamaica. It is suggested that: (1) the island of Jamaica may represent the original position of a bend or discontinuity in the northern Caribbean Plate boundary; (2) the present tectonic regime may indicate the complex modification of a regional stress field at a discontinuity in an otherwise linear shear zone; (3) the island represents a tectonically maintained mass excess; and (4) the observed rapid uplift along the island's north coast may be related to compression-induced reverse faulting.

Dixon, T. H.↗
NASA NTRS1982

Evaluation of photographic enhancements of Landsat imagery

The photographic processing of color Landsat imagery was evaluated to determine the optimal enhancement techniques. Twenty-six images were examined to explore the effects of gamma values upon image interpretation in a subarctic environment. Gamma values were varied on the images of bands 4 through 7 prior to the creation of the color composites. This yielded color-composited images with various color balances. These images were evaluated in terms of visible geological features (drainage, lineaments, landforms, etc.) and landcover features (exposed rock and ground, coniferous forest, etc.). The results indicate that the most informative images are created by using gamma values of 2.0 for band 4, 1.0 for band 5, and 2.0 for band 6 or 7. Other photographic enhancements tend to enhance some features at the expense of others.

Dean, K. G.↗
NASA NTRS1982

Thermal infrared pushbroom imagery acquisition and processing

A 9-element focal plane detector array and signal processing electronics was developed and delivered in December 1977. It was integrated into a thermal infrared imaging system using LSI microprocessor image processing and CRT display. After three years of laboratory operation, the focal plane has demonstrated high reliability and performance. On the basis of the 9-channel breadboard, the 90-element Aircraft Pushbroom IR/CCD Focal Plane Development Program was funded in October 1977. A follow-on program was awarded in July 1979, for the construction of a field test instrument and image processing facility. The objective of this project was to demonstrate thermal infrared pushbroom hard-copy imagery. It is pointed out that the successful development of the 9-element and 90-element thermal infrared hybrid imaging systems using photoconductive (Hg,Cd)Te has verified the operational concept of 8 to 14 micrometer pushbroom scanners.

Brown, T. J.↗
NASA NTRS1981

Information density and efficiency of two-dimensional /2-D/ sampled imagery

Information density and efficiency (i.e., the ratio of information density to data density) are used as criteria for assessing the quality of 2-D sampled and quantized imagery as a function of the statistical properties of random radiance fields, the spatial response (PSF or MTF) and sensitivity of imaging systems, and the sampling and quantization intervals. Computational results are intuitively satisfying: they are consistent with experimental and theoretical results obtained by earlier investigators concerned with the performance of TV cameras, and they provide useful guidelines for optimizing the design of line-scan and sensor-array imaging systems, especially if these systems use a digital communication link for transmitting data.

Huck, F. O.↗
NASA NTRS1982

Amplitude calibrating the Seasat SAR imagery

The Seasat Synthetic Aperture Radar is described with emphasis placed on those aspects of the system that affect the amplitude calibration of the radar. Imagery produced by several Seasat passes over Death Valley, California are examined in an effort to determine the reproducibility of the data and the potential for relative and absolute calibration of the overall SAR image data set.

Held, D.↗