As Landsat 7 acquires clear scenes over Africa (less than or equal to 20 percent cloud cover), the Landsat Project is automatically processing those scenes to an L1T, applying precision ground control and the SRTM DEM for geometric correction. These scenes are accurate to within 30m. There are four areas of the continent that are still under investigation due to poor geometric adjustments (Nile region, two areas in southern Africa, Madagascar). These will be reprocessed and come online in late May. Scenes can be found at:
+ GloVis: Collection>Landsat Science>Standard L1T
+ EarthExplorer: under 1. Select your dataset, choose Landsat Science>SLC-off L1T Std L1T
USGS Landsat Website
Safeguarding freshwater resources is crucial, and while scientists use a variety of ground-based techniques to gauge water quality, the Landsat program has provided water quality data from orbit for decades.