The U.S. ASTER science team activities
Explore the source record for details and available documents.
ASTER ERSDAC VNIR SWIR↗
Engineering topics
Gillespie, A. R.
Publications and source records attributed to Gillespie, A. R..
The U.S. ASTER Science Team activities
Explore the source record for details and available documents.
ASTER↗
Remote Sensing of Earth's Surface and Atmosphere: Interdisciplinary Scientific Commission A of the COSPAR Plenary Meeting, 29th, Washington, DC, 28 Aug. - 5 Sep., 1992
This conference reviewed the recent developments in remote monitoring of surface temperatures, which will be significant in future global change studies. Various techniques to derive surface temperature from existing and future remote sensing systems such as earth observing system (EOS) are discussed. Five sessions were held: (1) The nature of the problem of remote sensing of surface temperatures; (2) Surface temperature measurements from current satellites; (3) Modeling and surface observations of various techniques to measure temperature and/or emissivity, modeling of vegetation; (4) The effects of variable spectral emissivity from the determination of surface kinetic temperature using multispectral thermal infrared measurements; and (5) Future satellite systems including EOS/ASTER, EOS/MODIS-N, and EOS/AIRS.
Kahle, A. B.↗
Calibrating AIS images using the surface as a reference
A method of evaluating the initial assumptions and uncertainties of the physical connection between Airborne Imaging Spectrometer (AIS) image data and laboratory/field spectrometer data was tested. The Tuscon AIS-2 image connects to lab reference spectra by an alignment to the image spectral endmembers through a system gain and offset for each band. Images were calibrated to reflectance so as to transform the image into a measure that is independent of the solar radiant flux. This transformation also makes the image spectra directly comparable to data from lab and field spectrometers. A method was tested for calibrating AIS images using the surface as a reference. The surface heterogeneity is defined by lab/field spectral measurements. It was found that the Tuscon AIS-2 image is consistent with each of the initial hypotheses: (1) that the AIS-2 instrument calibration is nearly linear; (2) the spectral variance is caused by sub-pixel mixtures of spectrally distinct materials and shade, and (3) that sub-pixel mixtures can be treated as linear mixtures of pure endmembers. It was also found that the image can be characterized by relatively few endmembers using the AIS-2 spectra.
Smith, M. O.↗
Enhancement of time images for photointerpretation
The Thermal Infrared Multispectral Scanner (TIMS) images consist of six channels of data acquired in bands between 8 and 12 microns, thus they contain information about both temperature and emittance. Scene temperatures are controlled by reflectivity of the surface, but also by its geometry with respect to the Sun, time of day, and other factors unrelated to composition. Emittance is dependent upon composition alone. Thus the photointerpreter may wish to enhance emittance information selectively. Because thermal emittances in real scenes vary but little, image data tend to be highly correlated along channels. Special image processing is required to make this information available for the photointerpreter. Processing includes noise removal, construction of model emittance images, and construction of false-color pictures enhanced by decorrelation techniques.
Gillespie, A. R.↗
Lithologic mapping of silicate rocks using TIMS
Common rock-forming minerals have thermal infrared spectral features that are measured in the laboratory to infer composition. An airborne Daedalus scanner (TIMS) that collects six channels of thermal infrared radiance data (8 to 12 microns), may be used to measure these same features for rock identification. Previously, false-color composite pictures made from channels 1, 3, and 5 and emittance spectra for small areas on these images were used to make lithologic maps. Central wavelength, standard deviation, and amplitude of normal curves regressed on the emittance spectra are related to compositional information for crystalline igneous silicate rocks. As expected, the central wavelength varies systematically with silica content and with modal quartz content. Standard deviation is less sensitive to compositional changes, but large values may result from mixed admixture of vegetation. Compression of the six TIMS channels to three image channels made from the regressed parameters may be effective in improving geologic mapping from TIMS data, and these synthetic images may form a basis for the remote assessment of rock composition.
Gillespie, A. R.↗
Mapping alluvial fans in Death Valley, California, using multichannel thermal infrared images
Alluvial fans have been mapped in Death Valley, California using NASA's 8-12 micron six-channel airborne Thermal Infrared Multispectral Scanner (TIMS). Both composition and relative age differences were recognized. Age unit boundries are generally consistent with those obtained by conventional mapping. Composition was verified by field investigation and comparison with existing geologic maps. Bedrock and its young derived fan gravels have similar emissivities. The original composition of the fans is modified by differential erosion and weathering, permitting relative age mapping with TIMS.
Gillespie, A. R.↗
Eruption age of an approximately 100,000-year-old basalt from Ar-40/Ar-39 analysis of partially degassed xenoliths
Eleven samples from five partially degassed Mesozoic granitic xenoliths and two late Pleistocene host basalt samples from Sawmill Canyon in Sierra Nevada, California, have been analyzed using stepwise Ar-40/Ar-39 dating techniques. The petrography and analytic techniques are described and the results are presented. Isotopic compositions of Ar released from the xenoliths in several extraction steps at temperatures below about 900 C were colinear in Ar-36/Ar-40 versus Ar-39/Ar-40 diagrams and defined isochrons, giving a mean age of degassing of 119,000 + or - 7000 yr. Ar-40 extracted at higher temperatures included ancient radiogenic Ar-40 that never diffused from the xenoliths during immersion in the magma. This Ar-40 caused an increase in the apparent age for the high-temperature extractions. The high precision of the eruption age determined by this method is comparable to that obtained elsewhere by conventional K/Ar dating of sanidine.
Gillespie, A. R.↗
Eruption age of a Pleistocene basalt from Ar-40-Ar-39 analysis of partially degassed xenoliths
Explore the source record for details and available documents.
Gillespie, A. R.↗
Correlation of infrared reflectance ratios at 2.3 microns/1.6 micron and 1.1 micron/1.6 micron with delta O-18 values delineating fossil hydrothermal systems in the Idaho batholith
Reflectance ratios from laboratory spectra and airborne multispectral images are found to be strongly correlated with delta O-18 values of granite rocks in the Idaho batholith. The correlation is largely a result of interactions between hot water and rock, which lowered the delta O-18 values of the rocks and produced secondary hydrous material. Maps of the ratio of reflectivities at 2.3 and 1.6 microns should delineate fossil hydrothermal systems and provide estimates of alteration intensity. However, hydrous minerals produced during deuteric alteration or weathering cannot be unambiguously distinguished in remotely sensed images from the products of propylitic alteration without the use of narrow-band scanners. The reflectivity at 1.6 micron is strongly correlated with rock density and may be useful in distinguishing rock types in granitic terranes.
Gillespie, A. R.↗
Geologic utility of improved orbital measurements
From a geologists point of view, the most important use of orbital cameras is probably to provide spatial or context information in remote areas. This information can be extracted even from broad-band, single channel images provided that the spatial resolution is adequate for the problem at hand. Topographic information, usually provided by stereoscopic images, is next in importance. Any satellite system designed to satisfy general geologic requirements must produce stereo images, preferably with large base/height ratios of 0.5 or more. Satellite coverage at different illumination geometries could provide low Sun angles for regions of low relief where topography must be accentuated, and high Sun angles for areas of high relief or when multispectral data are being collected. Thus a different polar orbit than that of LANDSAT would be advantageous. The extended spectral sensitivity of scanner permits interferences of the composition of rocks in the scene to be drawn directly, rather than from contextual clues.
Gillespie, A. R.↗
Artifacts in digital images
Three kinds of artifacts unique to digital images are illustrated, namely aliasing caused by undersampling, interference phenomena caused by improper display of images, and harmonic overtones caused by quantization of amplitudes. Special attention is given to undersampling when the sample size and interval are the same. It is noted that this situation is important because it is typical of solid-state cameras. Quantization of image data of necessity introduces energy at harmonic overtones of the image spectrum. This energy is aliased if the frequency of the overtones is greater than 0.5 cycle/pixel. It cannot be selectively removed from the image through filtering, and the best way to suppress it is to maximize the amplification of the sensor before digital encoding.
Lorre, J. J.↗
Use of thermal-inertia properties for material identification
It is noted that a knowledge of the thermal inertia of the earth's surface can be used in geologic mapping as a complement to surface reflectance data as provided by Landsat. Thermal inertia, which is a body property, cannot be determined directly but can be inferred from radiation temperature measurements made at various times in the diurnal heating cycle, combined with a model of the surface heating processes. A model of this type is developed and applied along with temperature measurements made in the field and by satellite to determine thermal properties of surface materials. An example from a test site in western Nevada is used to demonstrate the utility of this technique.
Schieldge, J. P.↗
Construction and interpretation of a digital inertia image
An image representing the thermal inertia in the vicinity of Pisgah Crater and Lavic Lake in Southern California has been generated from visible, near IR, and thermal images taken from aircraft. Construction of the thermal inertia image required radiometric calibration and geometric rectification of the acquired images as well as registration to a topographic map. The Kahle thermal model used in the construction of the thermal inertia image requires specification of albedo, topographic slope and slope azimuth, diurnal temperature range and local meteorological conditions. Albedo information was derived from the visible image; digital topographic information was computed from digitized stereo aerial photographs; and thermal ranges were calculated by subtracting the predawn from the afternoon thermal image data. Our computed values of thermal inertia were in close agreement with published values for similar surface materials. Thermal inertia provides complementary information to conventional images of reflected solar radiation for use in lithologic mapping.
Gillespie, A. R.↗
Comparison of Skylab and LANDSAT images for geologic mapping in Northern Arizona
The author has identified the following significant results. It was found that based on resolution, the Skylab S190A products were superior to LANDSAT images. Based on measurements of shoreline features in Lake Mead S190A images had 1.5 - 3 times greater resolution than LANDSAT. In general, the higher resolution of the Skylab data yielded better discrimination among rock units, but in the case of structural features, lower sun angle LANDSAT images (50 deg) were superior to higher sun angle Skylab images (77 deg). The most valuable advantage of the Skylab over the LANDSAT image products is the capability of producing stereo images. Field spectral reflectance measurements on the Coconino Plateau were made in an effort to determine the best spectral band for discrimination of the six geologic units in question, and these bands were 1.3, 1.2, 1.0, and 0.5 microns. The EREP multispectral scanner yielded data with a low signal to noise ratio which limited its usefulness for image enhancement work. Sites that were studied in Arizona were Shivwits Plateau, Verde Valley, Coconino Plateau, and Red Lake. Thematic maps produced by the three classification algorithms analyzed were not as accurate as the maps produced by photointerpretation of composites of enhanced images.
Goetz, A. F. H.↗
Thermal inertia imaging - A new geologic mapping tool
A thermal model of the earth's surface has been developed and used to determine the thermal inertia of a test site in the Mojave Desert, California. The model, which includes meteorological heating terms as well as radiation and conduction heating terms, is used with remotely sensed surface temperature and reflectance data to determine the thermal inertia of the surface materials at the test site. The thermal inertia is displayed in image form, and can aid in the differentiation of the various lithologic materials in the test site. Since this thermal property is representative of the upper several cm of the surface, it complements visible and reflected near-IR image data.
Kahle, A. B.↗
The detection of geothermal areas from Skylab thermal data
Skylab-4 X-5 thermal data of the geysers area was analyzed to determine the feasibility of using midday Skylab images to detect geothermal areas. The hottest ground areas indicated on the Skylab image corresponded to south-facing barren or sparsely vegetated slopes. A geothermal area approximately 15 by 30 m coincided with one of the hottest areas indicated by Skylab. This area could not be unambiguously distinguished from the other areas which are believed to be hotter than their surroundings as a result of their topography, and micrometeorological conditions. A simple modification of a previous thermal model was performed and the predicted temperatures for the hottest slopes using representative values was in general agreement with the observed data. It is concluded that data from a single midday Skylab pass cannot be used to locate geothermal areas.
Siegal, B. S.↗
Detectability of geothermal areas using Skylab X-5 data
The results are presented of a study which was undertaken to determine if data from a single near-noon pass of Skylab could be used to detect geothermal areas. The size and temperature requirements for a geothermally heated area to be seen by Skylab S-192 MSS X-5 thermal sensor were calculated. This sensor obtained thermal data with the highest spatial resolution of any nonmilitary satellite system. Only very large hot areas could be expected to be unambiguously recognized with a single data set from this instrument. The study area chosen was The Geysers geothermal field in Sonoma County, California, the only geothermal area of significant size scanned by Skylab. Unfortunately, 95% of the Skylab thermal channel data was acquired within 3 hours of local noon. For The Geysers area only daytime X-5 data were available. An analysis of the thermal channel data (10.2 to 12.5 um) revealed that ground temperatures determined by Skylab were normally distributed. No anomalous hot spots were apparent. Computer enhancement techniques were used to delineate the hottest 100 and 300 ground areas (pixel, 75 m by 75 m) within the study region. It was found that the Skylab MSS with the X-5 thermal detector does not have sufficient spatial resolution to locate unambiguously from daytime data any but the largest and hottest convectively created geothermal features, which in general are prominent enough to have been previously recognized.
Siegal, B. S.↗