The Efficiency of Landsat TM and ETM + Thermal Data for Extracting Soil Information in Arid Regions
J. Agric. Sci. Technol
A knowledge of soil surf ace conditions, especially desert crust, salt crust and desert varnish is usef ul f or improving classif ication of remotely sensed data. Desert crust can generate high levels of ref lectance, similar to those areas with high salt concentration and non-saline soil. Theref ore, soil surf ace crusts might bias thematic remote sensing of soils. In this study, we evaluated the ef f iciency of the Thematic Mapper (TM) and Enhanced Thematic Mapper plus (ETM +) ref lective and
... +) ref lective and thermal bands in detecting crusted surfaces and soil salinity conditions. The study areas were Ardakan, Damghan, Lut Desert, Q om, and Abarkooh which are located in arid regions of Iran. To assess the Landsat TM thermal data f or detecting land cover types, the f ollowing steps were taken: 1) determination of correlation coef f icients between TM wavebands, 2) assessment of the relationship between TM thermal and TM ref lective bands on land cover types, 3) assessment of the relationship between soil salinity and TM Digital Numbers (DN), 4) two dimensional Feature Space (FS) analysis of the training samples, 5) f ield sampling, 6) image classification and accuracy assessment, and 7) comparison of surf ace ref lectance of dif f erent soil surf ace types. The results show that the trend of correlation coef f icients of TM6 with ref lective bands is completely dif f erent f rom the correlation between ref lective bands. The behaviour of the thermal band on gypsif erous soils is completely dif f erent f rom that on saline soils. Moreover, with an increasing correlation between soil salinity and ref lective bands, the correlation between soil salinity and the thermal band decreases. In image classification , the thermal band improved the separability of the crusted and gravely classes. Theref ore the TM/ETM + regions of the electromagnetic spectrum have complementary capabilities f or spectral separability of gravely and crusted surf aces. In general, selection of the TM/ETM + thermal band combination is an important step f or classif ying the remote sensing data and f or securing class separability of gravely and crusted surf aces in arid regions. We also concluded that TM/ETM + thermal bands may contain inf ormation complementary to the TM/ETM + ref lective bands and theref ore this combination of the TM/ETM + thermal and ref lective bands provide a viable method f or soil salinity studies in arid regions.