NASA's Web Enabled Landsat Data (WELD) project generates global composited and mosaicked True color Landsat 7 Enhanced Thematic Mapper Plus (ETM+) 30 meter resolution imagery in monthly and annual time increments. The layers are processed to ensure consistency across time to allow for direct comparison of land cover characteristics and changes over the course of approximately 25 years. Also available are Normalized Difference Vegetation Index (NDVI) annual and monthly imagery. This layer is useful for monitoring vegetation conditions and can be used to identify areas undergoing land cover changes. It also provides information on the health of vegetation and can assist farmers and resource managers to monitor the health and development of their crops and fields over the growing season. The imagery is currently available for 1 December 2008 to 1 November 2011 and will eventually include six more sets of 3-year epochs starting with the 1985 epoch.
View the Global WELD imagery with Worldview
Global, annual surface reflectance: http://go.nasa.gov/2kG8Gda
Global, monthly surface reflectance: http://go.nasa.gov/2lr9gQr
Global, annual NDVI: http://go.nasa.gov/2kFXai6
Global, monthly NDVI: http://go.nasa.gov/2lrcJyn
Visit Worldview at https://worldview.earthdata.nasa.gov to explore WELD and more than 200 other imagery layers!