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Experimental data were acquired for a study of the effects of variable atmospheric path on the spectral signals obtained by remote sensors in the optical region of the spectrum. Multichannel optical-mechanical scanners which provide calibrated apparent spectral radiance data were flown over agricultural test sites, and passes were made at several different altitudes between 2000 and 10,000 ft. The quantitative results compare favorably with qualitative theoretical predictions. Optical-mechanical scanners and aerial photographic systems are compared to show the relative importance of potentially detrimental atmospheric path effects with regard to the operation of these systems in remote sensing. then the positive term ~Lv/ah (2) could well dominate, so that the apparent target radiance Lff would increase with altitude. Conversely, if the actual target radiance were quite large, then the negative term a~-n/ah could well dominate, thus producing a decrease in apparent radiance with altitude. The radiance difference between two targets, a and b, of actual radiance L, and L ~, respectively, is given by zlL" .

Interpretation of imagery requires contrast between the object being sought and its background. A technique is described for increasing the contrast of selected objects based on their spectral reflectance or emittance characteristics, and two applications are discussed. Means for implementing this technique with an optical-mechanical scanner, multielement dispersing spectrometer, and electronic signal processing equipment are discussed.

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