Remote sensing study of surface temperature variability with vegetation cover, by Landsat ETM applied to agricultural management

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Optical remote sensing (RS) is used to provide an effective knowledge base for advanced agriculture research (Ambast et al., 2002). Visible - Near Infrared (NIR) wavelengths offers the ability to monitor landscape process that are controlled by several surface parameters (Jacob et al., 2002; Price, 1992). Most commonly a simple or normalized ratio between the visible red and the NIR spectral wavebands are used for vegetation indices (VI). Several vegetation indices have been developed using the linearity of the NIR versus red reflectance as an indication of the green biomass. Some of the more sophisticated indices attempt to neutralize the soil influence by using a parameter or curve for bare soils. The weighted difference vegetation index (WDVI) developed by Clevers (1988) is one of those that corrects for the soil affects.

During early stages of vegetation stress, the cover might stay relatively constant but the surface temperature (Ts) may vary greatly because of changes in the soil physical properties including moisture and soil color (Bastiaanssen et al., 2000). Some studies have focused on the surface temperature and VI relation (VI/Ts) (Boegh et al., 1999; Nemani and Running, 1989). Moran et al., (2002) showed that scatter plots of remotely sensed (RS) surface temperature and VI often yield trapezoid shapes and explained this, by the differences in surface properties related to the effect on VI/Ts slopes for similar surface and atmospheric conditions. These trapezoid plots span a variety of surface types. The maximum Ts agree with bare soil conditions and the lowest Ts with full vegetation cover (VC). The interpretation of Ts for sparse VC, which is widespread in semi-arid regions, is not straightforward. Studies hav...

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