Abstract

The Fraunhofer line discriminator (FLD) is an airborne electro-optical instrument which permits daylight detection of materials on the Earth's surface which have been stimulated to luminesce by solar ultraviolet and visible light. This instrument uses glass spacer Fabry-Perot filters of narrow bandwidth (<0.1 nm) to isolate a Fraunhofer line of interest (Hemphill and others, 1983). To measure the luminescence of a material, the FLD computes from reflected light the ratio of the central intensity of a Fraunhofer line to the solar continuum a few tenths of a nanometer distant; it then compares this ratio with a conjugate measurement in skylight and direct sunlight. Luminescence is indicated where the ratio measured from the target material exceeds the ratio measured from skylight and direct sunlight.

© 1984 Optical Society of America