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 cτ/2, determined by the pulse length τ, 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 104to 105 times better than that achieved by the Raman method.
Robert L. Byer and Max Garbuny, "Pollutant Detection by Absorption Using Mie Scattering and Topographic Targets as Retroreflectors," Appl. Opt. 12, 1496-1505 (1973)