SPATIAL DEPENDENCY OF SOIL LINE COEFFICIENTS DERIVED FROM LANDSAT ETM+ AND MODIS IMAGERY IN KYRGYZSTAN

摘要

Remotely sensed data in vegetated lands always consist of signals from vegetation, soil surface and path radiance. In order to analyze aspects of vegetation such as estimation of vegetation vigor or aboveground biomass, noise from soil surface and path radiance must be properly treated. The effects of path radiance are removed by atmospheric correction and the background reflection from soil surface is taken into account in some vegetation indices such as TSAVI (Transformed Soil Adjusted Vegetation Index) or SAVI (Soil Adjusted Vegetation Index). In these two vegetation indices, soil line coefficients, a (gain) and b (offset) shall be known to apply those vegetation indices in the study area. However, these soil line coefficients are dependent on existing soil types in the study area, especially on soil properties such as soil color, organic matter content and metal content. The spatial characteristics of soil line coefficients must be well understood in the analysis. This research studied, 1) the spatial dependency of soil line coefficients using geo-statistics, 2) differences in coefficients a and b among soil types which are categorized in the FAO soil classification system using the Student t-test, and 3) consistency between soil line coefficients derived from temporal Landsat TM data and those derived from temporal MODIS data by comparing their coefficients in Kyrgyzstan, a semi-arid region. In conclusion, 1) a value, the gain of the soil line shows a range in the semi-variograms.2) Soil line coefficients a and b for the seven soil types that exist in Kyrgyzstan are significantly different by statistical test.3) Coefficients derived from MODIS data and Landsat TM data have almost the same values.4) Vegetation information in vegetated lands can be more accurately obtained by using proper soil line coefficients corresponding to soil types in the FAO soil map.5)A variety of soil colours for one type of soil and similarity of land slope classes may affect the identification of soil coefficients in different soil types.