Improved retrievals for satellite-based multispectral infrared remote sensing of volcanic clouds

Use of satellite thermal infrared data for volcanic cloud studies has ignored atmospheric corrections. In this dissertation, HIRS/2, AVHRR and GOES data were used to discriminate volcanic clouds and retrieve properties of volcanic clouds of the 1982 eruption of El Chichón, 1997 eruption of Montserrat and 1992 eruption of Spurr. Three atmospherically corrected retrieval models and a new volcanic cloud discrimination procedure were developed. Results showed that: (1) The new discrimination procedure improved the detection of volcanic clouds, especially in moist tropical atmospheres where water vapor interferes with the discrimination. The new cutoff procedure is essential to detect small scale volcanic clouds in moist tropical regions where numerous volcanic cloud pixels have positive BTD values. (2) Multiband thermal HIRS/2 data can be used to retrieve properties of volcanic clouds with both sulfate and silicate particles, and the retrieval model based on HIRS/2 data can be directly applied to other detectors such as MODIS, which has similar thermal infrared channels to HIRS/2 and much higher spatial resolution. (3) A new lookup table retrieval model with atmospheric corrections considers the transmittance differences in the two thermal bands of GOES and AVHRR and can be used to perform retrievals on volcanic cloud pixels with positive BTDs. Atmospheric corrections mainly affect the retrieved results of volcanic cloud pixels with higher band 4 brightness temperatures and larger BTD values. (4) A polynomial retrieval method based on emissivity improves and tests retrievals of volcanic cloud with low optical depths. It can be used to supplement previous methods at the edges of large volcanic clouds, in small clouds and aged ones.