Numerical Analysis of Landsat Thematic Mapper Images of Antarctica: Surface Temperatures and Physical Properties

Abstract

Landsat-5 Thematic Mapper (TM) data from Dronning [Queen] Maud Land, Antarctica, have been analysed to provide insights into physical properties of the ice sheet. Brightness (at-satellite) temperatures calculated from digital numbers of the thermal band (TM band 6), using state-of-the-art equations and constants (Markham and Barker 1986), are 8° to 20°C lower than temperatures measured on the surface. Such differences cannot be ascribed to atmospheric absorption or to emissivity variations; instead, they suggest errors in either the sensor or instrument calibration for the temperature range 0° to −20°C. The results indicate an excess gain factor of about 1.63. The TM band 6 data seem to reproduce faithfully the relative temperature variations across the surface. Principal components (PCs) calculated for TM bands 2, 3, 4, 5, and 7 are presented for a region of the interior ice sheet. PCs are superior to individual bands or combinations of bands for analysing the main characteristics of an image, such as rendition of surface topography (mostly given in PCl), and for distinguishing between different surface materials (mostly given in PCs 2 and 3). Band ratioing was most useful for enhancing subtle albedo variations, such as those caused by changes in surface properties due to melting. TM data of the region, collected 18 d apart, show large changes on the snow surface; strong patterns shown in PC2 and TM bands 5 and 7 of the earlier image were nearly faded 18 d later. These strong patterns are not present at visual wavelengths or in the thermal band, and we believe they reflect wind-related variations in the physical properties of the snow.