Vegetation along the riparian corridor of the lower Pecos River in the United States hasbeen dominated by saltcedar for the past century. In 1999 through 2004, herbicides weresprayed from helicopters along some sections of the river to reduce saltcedar infestation. Herewe describe a simple methodology based on satellite remote sensing for monitoring the impact ofthe saltcedar control measures. Data from the Landsat 7 Enhanced Thematic Mapper Plus(ETM+) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)obtained in 1999 through 2004 over a section of the Pecos near Mentone, Texas were used forthe present study. Herbicides were applied in September of each year. A normalized differencevegetation index (NDVI) image was derived from the satellite data for one growing season, andthen it was compared to an NDVI image from the previous year. Using the write memoryinsertion change detection technique, we superimposed the NDVI image pair. Thesuperimposed image highlighted areas where vegetation was lost during the interval between thetimes when the two satellite data sets were acquired. The areas of vegetation loss indicated bythe change detection image coincided well with the areas where herbicides were applied in thesame time interval. Since the riparian vegetation previously was dominated by saltcedar,identifying the areas of vegetation loss in this case is useful in assessing the long-term impact ofthe herbicide treatments. The same type of change detection technique was also used to locateareas of native vegetation recovery after the herbicide application.
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