Recovery of spectral emissivity from Thermal Infrared Multispectral Scanner imagery acquired over a mountainous terrain: A case study from Mount Etna Sicily

The estimation of ground radiance and emissivity from Thermal Infrared Multispectral Scanner (TIMS) data is strongly dependent on the atmospheric correction applied to these data. Since such corrections are a function of the atmospheric path between the sensor and ground, correction techniques that do not consider the topographic variations within a scene can introduce appreciable error in the estimation of the atmosphere effects. In this paper, we describe the development and application of a variable-elevation atmospheric correction procedure. Our objective was to incorporate changes in target altitude into a general atmosphere correction strategy. This procedure was tested on a TIMS data set acquired over Mt. Etna, Italy in July 1986. The methodology adopted in this study is based on the use of the LOWTRAN radiative transfer code and a digital elevation model (DEM) registered to the image data. The image data are divided into a series of layers, based on elevation, and a separate atmosphere correction is applied to each layer. Maps of emissivity estimates derived with the variable-elevation approach were compared with geologic maps of the Etna flow fields. Prior to the variable-elevation correction, the emissivity spectra of long lava flows appeared to vary with elevation. Following the variable-elevation correction, many of these spectral artifacts were removed from the emissivity maps. In addition, the variable-elevation correction increased our ability to discriminate individual lava flows.