Relationship of aircraft radiometric measurements to bare ground on semi-desert landscapes in central Australia.

Abstract

Radiance values in Landsat MSS bands were measured over five landscapes typical of central Australia: a calcareous plain, an eroded calcareous plain, a gibber plain, a floodplain and a savannah woodland. using an aeroplane-mounted isotech four band radio- meter flown at a height which gave Landsat pixe!-sixed sampling areas. Forty-five radiometric variables derived from these radiance data were correlated with the amount of bare soil interpreted frotn aerial photos. On the calcareous plains and the floodplain, the highest correlations were obtained with the visible bands, Band 4 and Band 5, and the difference between them. On the gibber plains and savannah woodlands the best correlations were obtained with the ratio of Band 5 to Band 7 and the subtraction ratio of B4-B5/ B4-B7. A series of linear relationships were developed linking bare ground \vith radiometric variables which expl'ained between 705% and 85% of the variation. Multiple regression analysis on the radiometer indiccs most highly correlated with total bare ground showed that inclusion of other cover variables such as litter, shadow, soil colour and herbage covcr increased the variation explained by only 5-10%. A test of the effect of differences in solar elevation angle on the 45 radiometric variables showed that the radiance values in each band and differences between them \$cue significantly affected. Eight indices were affected to a lesser degree and may bc useful for multi- temporal work. Some considerations of the use of the selected indices for practical landscape monitoring are also discussed.