Remote sensing with infra-red heterodyne radiometers

Abstract

The narrow spectral bandwidth capability of heterodyne radiometers can be utilized to construct highly selective pollutant sensing instruments. The infra-red spectral region is favourable due to the availability of pollutant absorption lines and the wavelength dependence of heterodyne sensitivity. We review the types of sensing systems which can make use of heterodyne techniques, including comments about the type of lasers which can serve as local oscillators. Sensitivity calculations of passive heterodyne radiometers to NO, CO₂, and SO₂ are then presented. Our concluding discussion involves the use of a heterodyne receiver in an active NO sensing system which is based on infra-red fluorescence.