Source: USGS Landsat Mission
On August 21, 2012, all newly processed Landsat data will have updated filenames and metadata to better align all 40 years of Landsat data and to prepare for new data from the Landsat Data Continuity Mission that is scheduled to launch on February 11, 2012.
Details:
+ https://www.usgs.gov/landsat-missions/Landsat_Metadata_Changes.php

Above the Earth, Below the Surface: Landsat’s Role in Monitoring Water Quality
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.