Pollutant Detection by Absorption Using Mie Scattering and Topographic Targets as Retroreflectors

Remote pollutant measurement by absorption using topographical reflectors or atmospheric Mie scattering as a distributed reflector offers increased range and sensitivity compared to that achieved by Raman or resonance backscattering methods. The use of opographical reflectors offers the advantage of a single-ended absorption measurement for ranges up to 10 km and sensitivities to ess than 0.01 ppm for a 10-mJ, 100-nsec transmitted pulse. The distributed Mie reflector permits absorption measurements over a depth ctau/2, determined by the pulse length tau, and allows ranging by time-of-flight measurement. For a 100-mJ, 100-nsec pulse sensitivities to 0.3 ppm at a 15-m depth resolution to ranges of 1-4 km are possible. This sensitivity is 10(4)to 10(5) times better than that achieved by the Raman method.