In 2000, NASA sponsored the creation of an orthorectified Landsat 7 mosaic of all of Earth’s landmasses (with the exception of Antarctica) as part of the GeoCover 2000 project. This mosaic has gone on to spur a flurry of geo-commerce as companies from around the world create enhanced versions of this mosaic using the GeoCover Landsat data. Let’s take a look how…
USGS provided NASA with 8500 Landsat 7 ETM+ georectified scenes (processed to L1G) that were collected between 1999 and 2002 in order to create the GeoCover mosaic. NASA then contracted EarthSat (now part of MDA Federal) to orthorectify the Landsat data and create a pan-sharpened (14.25 m spatial resolution) false-color (ETM+ bands 7, 4, 2) seamless mosaic. NASA then made both the orthorectified Landsat scenes and the pan-sharpened mosaic free to the public. Since that time, both domestic and international companies have taken advantage of this free data to create proprietary pseudo-true color mosaic products.
After creating the NASA GeoCover mosaic, EarthSat created a circa-2000 Landsat mosaic called NaturalVue™. NaturalVue™ uses the five lower spectral bands of Landsat 7 plus the panchromatic-band to create imagery that approximates natural color (with a proprietary algorithm). This data set was originally used as the Google Earth™ base map.
In spring 2006, Google Earth™ announced its switch to TruEarth® for the Google Earth™ base map. TruEarth® is a TerraMetrics® product also made from the same orthorectified Landsat 7 data, but produced by TerraMetrics® using its proprietary natural-color processing.
The GeoCover 2000 mosaic was also converted to a pseudo-natural color data set called TerraColor by a San Diego-based geospatial company called Earthstar Geographics LLC. This product is used as the mid-resolution aerial imagery for MSN® Virtual Earth™.
And in February 2007, ComputaMaps, a South African geospatial data solutions company, announced the release of it’s BrightEarth™ product, another orthorectified Landsat 7 mosaic created by transforming the original NASA GeoCover mosaic with a proprietary algorithm.
(Update added May 3, 2007)
In May of 2007, an Australian company called GeoSage released “Spectral Transformer B742B321” a data processing tool that produces simulated natural-color imagery from the NASA GeoCover
Why these mosaic products should NOT be considered data
All of these mosaic products, including the original NASA GeoCover mosaic, should only be considered as imagery, NOT as data. Creation of all of these mosaics involved data resampling, data blending, and color balancing so, the pixel values or “digital numbers” that remain no longer have fidelity as reflective measurements made by the satellite.
For more information, see:
+ Landsat Data Base Map for Google Earth™
+ Landsat Data Part of MSN® Virtual Earth™
+ “ComputaMaps releases BrightEarth, a global natural color mosaic” Directions MagazineFeb. 9, 2007. PDF version.
+ “HighView | Spectral Transformer B742B321” (external link) PDF version.