Remote sensing can be a powerful tool for monitoring changes in semi-arid rangelands and the effects of management, but methods are still lacking to be able to accurately monitor the movements and impacts of livestock that often dominate grazing in such rangelands. In this report, a new method of monitoring livestock based on time differences in satellite-based measurements of “greenness” (NDVI, Normalized Difference Vegetation Index) is validated with unprecedented intensive measurements of forage biomass on rangelands in Kalama and Westgate Conservancies in northern Kenya.