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Mapping salt-affected soils in remote rangelands is challenging. We used Landsat 7 ETM data to facilitate digital mapping of gypsic and natric soil areas in the upper Colorado River drainage. Optimum index factor band combinations were used to explore the scene. Normalized difference ratio models and threshold values were developed by comparing spectral signatures with gypsic and natric soil areas verifi ed in the fi eld. Gypsic soil areas were mapped using the normalized difference ratio of Bands 5 and 7 with a threshold >0.11, probably related to the spectral refl ectance of gypsum within a few centimeters of the surface. All sites predicted to be gypsic soil areas were determined to be gypsic by fi eld assessment,...
Understanding spatial and temporal variation in net primary production (NPP), the amount of carbon fixed into biomass by vegetation, is a central goal of ecosystem ecologists. Optical remote sensing techniques can help address this need by providing accurate, consistent, and reliable approximations of photosynthetic activity at large scales. However, converting photosynthetic activity into NPP requires estimates of light-use efficiency, which has been shown to vary among vegetation types. In this study, we compare remotely sensed estimates of absorbed photosynthetically active radiation with ground-based NPP estimates to determine appropriate light-use efficiency values for grasslands and croplands. We contrast...