| This thesis reports on modelling and instrumentation developments in the field of gas correlation spectroscopy, a technique that employs the auto correlation between the features of an absorption spectrum of a gas in a cell with those of the same gas in an atmospheric path. While gas correlation spectrometers are widely used to detect ambient densities of atmospheric molecular species, this work focussed on remote sensing of gas constituents in the troposphere. The work built on the achievements of many others but most particularly on the NASA Measurement of Air Pollution from Satellites (MAPS) programme that pioneered the use of gas correlation as an orbital tropospheric remote sensor of trace gases during the shuttle flights' STS-2 on Nov. 12, 1981, STS-41G on Oct. 5, 1984, STS-59 on April 9, 1994, and STS-68 on Oct. 1, 1994.; The primary innovation in this body of work was the development of a digital microprocessor-based gas-cell-chopper correlation spectrometer. The use of on-chopper radiance targets and digital signal processing enabled the correlation spectrometer to be zeroed (balanced) without adding a second modulated black body reference signal. The digital method, by the elimination of thermally-sensitive analog components, also reduced the need to rely on external stabilisation of the instrument temperature to bring signal into an acceptable range. The application of these design concepts to hardware built as part of this dissertation resulted in tropospheric remote sensors with much reduced size, weight, power consumption and component costs.; This body of work is primarily a proof of concept of the digital gas-cell-chopper correlation method. It included modelling, instrument design, laboratory calibration and field trials with four correlation spectrometers. The work described includes: (a) the development of a signal and noise model that incorporates radiometric considerations, (b) the improvement and evaluation (under simulated tropospheric remote sensing conditions) of the analog-based Barringer Research Ltd. AES GASPEC, (c) the design, construction and testing of two instruments, GASCOFIL and GASCOSCAN, developed by the writer, to prove the idea of a digital design approach to gas correlation spectroscopy, (d) the design, construction and testing of MicroMAPS, a space-qualified CO remote sensor that used the digital approach, (e) the use of GASCOFIL and GASCOSCAN to make tropospheric gas concentration measurements, including SO2 from coal fired generating plants, SO2, HCl, and NO2 from smelters and forest fires, CO over roadways, CO and N2O over Southern Ontario and CO and OCS from the Galeras volcano five days before its eruption (Charland, Morrow, Nicholls and Stix, 1993). |
