Recent advances in correlation spectroscopy for the remote sensing of SO2

The COSPEC remote sensor is a spectroscopic system which utilizes the ultraviolet absorption bands of SO2 and the sky radiation at those wavelengths to measure SO2 plumes in the atmosphere. As a passive sensor, changes in backgrounds such as those due to sky-cloud variations, solar elevation, etc., affect the performance of the instrument, signal to noise ratios, and baseline stability. A setup procedure has been devised which minimizes the effects of background changes, and results in a virtually drift-free baseline. This procedure and the theoretical basis for its development will be presented. An example of its practical results has been the detection of a tall stack plume at 400 km from its source.