Atmospheric effects on radiation reflected from soil and vegetation as measured by orbital sensors using various scanning directions.
Ground-measured spectral reflectance data for Avondale loam and drought-stressed and unstressed wheat were converted into digital counts for spectral bands 5 and 7 of the Landsat Multispectral Scanner System (MSS). For dry loam, the differences between ratios of MSS bands 7-5 as determined from space and from ground level measurements were 2.3% for clear and 5.6% for turbid atmospheric conditions. By contrast, for wet loam the differences were 10.4 and 29.5%. We found that atmospheric conditions may cause a delay of from 3 to 7 days in the discrimination between drought-stressed and unstressed wheat. For oblique angle observations the atmospheric modification of ground-measured reflectances increased with angle at a greater rate in the 0/180 degrees azimuth than in the 90/270 degrees azimuth. Implications of this result are discussed for oblique angle Système Probatoire d'Observation de la Terre (SPOT), Mapsat, future multispectral linear array system imagery, and wide-angle imagery collected from scanners in high-altitude aircraft.
Slater
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University of Arizona, Optical Sciences Center, Tucson, Arizona 85721, USA.
Jackson
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