Optical and seasonal variations along the U.S.-Mexico border: an analysis with Landsat TM imagery

A multi-temporal border study was conducted with a series of seven Landsat Thematic images acquired during the 1992 growing season. Spatial and temporal variations across the border were analyzed with reflectance and thermal data. Vegetation index and brightness parameters were computed to study land use differences and their impact on vegetation and soil, temporal and phenological variations. The thermal data, in conjunction with the vegetation index results were used to infer differences in moisture, condition and stress throughout the wet and dry seasons. This was accompanied by a ground-based campaign to analyze the soil and biophysical properties of the surface. Soil color, texture and reflectance were measured on both sides of the border along with plant cover and biomass sampling. Significant differences in biomass cover and dry/green biomass ratios were found. The Mexican side had a more intense grazing use, which resulted in a lack of dry plant material, as well as lower amount of green growth. The normalized vegetation index (NDVI) and brightness clearly showed vegetation differences across the border while thermal differences were more subtle.