APPARATUS AND METHOD FOR REMOTE SENSING OF GASES, VAPOURS OR AEROSOLS

摘要

ABSTRACT (Figure 4)A remote sensor for detecting gas, vapour or aerosol comprisesmeans to measure the change in temporal coherence of light of a selectednarrow waveband when it interacts with the gas etc. The light can beprovided by a laser source or spectrally filtered sun light etc.Received radiation is split in to two beams by a Fresnel biprism andthen detected by a detector sensitised by a modulating reticle tointerference fringes. A glass delay plate of suitable thickness isplaced in the path of one of the beams such that only received radiationhaving a temporal coherence greater than a minimum determined by theplate thickness produces an output signal from detector. The minimumtemporal coherence is set higher than the temporal coherence of theilluminating radiation. In alternative arrangements a band-passtemporal coherence filter may be used and the sensor can be made tospectrally scan the field of view by using a tunable laser or a variablecentre frequency band-pass optical filter.