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Description:
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The application of remote sensing technology in evaluating the crop water stress index is hampered by soil background effects related to partial ground cover . This study investigates the explicit contribution of soil information as an added dimension to the Vegetation Index Temperature /Trapezoid method , as well as data fusion technique to increase visual interpretation of water stress to formulate a new index of water stress . The study was conducted in Lubbock and Hale counties which includes an irrigation study at USDA -ARS in 2006 -2008 , Texas Tech irrigation studies at N Quaker and New Deal in 2007 , and the AgriLife extension irrigation study in Halfway , TX in 2007 -2008 . Remote sensing missions were carried out using the Texas Tech Airborne Multispectral Remote Sensing System . Digital counts in Red and Near -Infrared images were converted to reflectance . Thermal Infrared images were converted into absolute temperatures using the known reflectance of calibration tarps and thermal sensors on the ground . Estimation of ground cover and the calculation of soil brightness were carried out using observed reflectance in the Red and NIR . The normalization of soil brightness into a Soil Brightness Index was carried out using the temporal reflectance values of soil brightness . Differences between surface temperature and air temperature were calculated . The fusion of the differences between the surface minus air temperatures , ground cover and soil brightness index into the Hue and Saturation & Intensity domain (respectively ) improved the identification of water stress levels and the non -living features . Degree of water stress seemed to follow the ground cover across locations . The non -stressed cotton was observed consistently to be above 60 percent ground cover . Below this value , cotton begins to experience some degree of stress which can be associated with the acclimation of cotton to plant -available -water . Low ground cover however , can be non -stressed , with soil brightness index approaching 0 . The 3 -dimenstional CWSI is applicable to cotton under various irrigation types . The ground cover estimates and normalized soil brightness improved the discrimination of water stress levels using the 3 -dimensional crop water stress index . |