Global Land Surveys

In the past, the U.S. Geological Survey (USGS) and NASA collaborated on the creation of four global land data sets from Landsat images: one from the 1970s, and one each from circa 1990, 2000, and 2005. Each of these global data sets was created from the primary Landsat sensor in use at the time: the Multispectral Scanner (MSS) in the 1970s, the Thematic Mapper (TM) in 1990, Enhanced Thematic Mapper Plus (ETM+) in 2000, and a combination of TM and ETM+ in 2005.

GLS2010

To extend this multi-decadal Landsat data collection, NASA and the USGS have again partnered to develop the Global Land Survey 2010 (GLS2010), a new global land data set with core acquisition dates of 2009-2010. The data will consist of both Landsat TM and ETM+ images.

The Landsat 7 ETM+ and Landsat 5 TM data incorporated into the GLS2010 data set must meet quality and cloud cover standards. Data recorded in 2011 will be used as needed to fill areas of low image quality or excessive cloud cover. The status graphic below displays the scenes already processed for GLS2010 and will be updated.

GLS1990

The GLS1990 data was created decades ago. The TM data used at the time were processed at ground stations all over the world, then brought back to the US and reprocessed to create similar products across the entire dataset. This approach, while necessary at the time, created very inconsistent radiometry and geometry. The geometry was corrected in 2006, but the radiometry remains poor in some areas.

To correct the radiometry of the GLS1990 dataset, all scenes have to be reacquired from international ground stations in raw format. These raw scenes would then be processed at USGS EROS in a single format, with consistent and up-to-date radiometric algorithms. Now 20 or more years old, some scenes may never be recovered, but the Landsat project expects to receive around 95% of the scenes (and hopes for more).

In the fall of 2010, the Landsat project sent requests to the international community and has been continually receiving GLS1990 raw data. All available raw scenes should be in the archive by mid-2011, when a reprocessing effort will commence.

All GLS datasets are scene-based, and can be searched and downloaded from Glovis or EarthExplorer.

Figure 1. GLS2010 Scenes Status as of May 9, 2012