Droughts are normal recurring climatic phenomena that affect people and the landscapes they occupy at many scales (locally, regionally, and nationally) for periods of time varying from weeks to decades. The spatial and temporal variability and multiple impacts of droughts present challenges for mapping and monitoring on all scales. Operational drought monitoring, by its very nature, requires repetitive measurements at the same location day after day, month after month, and year after year. Monitoring tools require reliable sources of time-series data at effective spatial and temporal scales to provide accurate and timely information. Satellite remote sensing is an obvious data source, supplying synoptic coverage of the land surface with objective, automated data collections for use in spatially specific models. Satellite information is especially appropriate over remote areas or areas with sparse field instrumentation.
