Direct snow-water equivalent measurement by air-borne gamma-ray spectrometry

Abstract

A direct air-borne technique to measure snow-water equivalent that utilizes the buildup of scattered gamma-radiation from 40K with increasing snow-water equivalent has been successfully tested. The variations in the shapes of the potassium, uranium and thorium gamma-ray spectra were determined from measurements on large radioactive concrete pads, using plywood sheets to simulate a uniform snow-water equivalent layer. The air-borne system was calibrated by flying at different altitudes over two test areas and converting the aircraft altitude to an equivalent layer of water. A series of nine flights at different altitudes over an area of unknown radioactivity gave results consistent with snow-water equivalent ground measurements of 142 mm and also with air-borne results from the standard two-flight technique. The single-flight technique has the advantage over the two-flight method that no ground soil-moisture measurements are necessary, no presnow flight is required and navigation problems in duplicating the two flight lines are avoided.