A technique is described for measuring hitherto unavailable, long range, air-to-ground total and direct transmittances simultaneously in the visible and near ir spectral regions from a point source in a real atmosphere. The technique involves a radar tracked aircraft with a flashing light source and a ground based, highly sensitive, multichannel, 180° field-of-view light receiving system with manual tracking provisions. Air-to-surface transmission measurements were carried out to maximum slant range of 100,000 yards (92 km) at different altitudes and weather conditions over Lake Michigan and Wisconsin farmland during March 1965. Total transmittances vs slant range for the visible and near ir regions are presented as smoothed, average curves and simplified exponential equations representing the least-square fit to the experimental data under specific weather conditions. Criteria for evidence of surface albedo differences are introduced, from which limited albedo effects are noted under cloudy, snow-covered surface conditions.
© 1968 Optical Society of AmericaFull Article | PDF Article
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