3.3.1 Geocover-LC
The Earth Satellite Corporation (EarthSat) contracted with the NASA in 1998 to
generate an orthorectified satellite image base (Tucker et al., 2004), and then contracted
with the National Imagery and Mapping Agency (NIMA) to produce a land cover map
of the earth’s landmasses. The GeoCover-LC product (Earth Satellite Corporation
2003) is the first moderate resolution land cover map of the world using Landsat
Enhanced Thematic Mapper (ETM+) and Thematic Mapper (TM) data. EarthSat used
a proprietary process to generate orthorectified tiles of ETM+ data for the Earth’s
landmasses with a 1.4 ha minimum mapping unit (accuracy equivalent to 1:200,000scale maps). The first set of maps was generated utilizing 1990 imagery and covers
North America and the Caribbean, Africa, Europe and east Asia. The second using
2000 data covers non-Amazonian South America, central and southeast Asia. Both
datasets consist of a 13-class land cover legend. Updated coverages for northern
Africa, Europe and east Asia were produced using 2000 data and a patented “Cross
Correlation Analysis.” This method detects change between the 1990 Landsat 4/5
images and the 2000 Landsat 7 images. The full Geocover classification is then
reconstructed from the older data and the changed data for the update. Although the
coverage was originally envisioned to be global, land cover has not been mapped for
Australia, New Zealand, the Amazon, and parts of northern Eurasia. Because it was
produced by a commercial entity, Geocover-LC products must be obtained under
license.
The Geocover-LC scheme has an uncertain degree of validation, and studies that
make use of the data in synthesis applications need to validate its use. For example,
some preliminary data indicates that Geocover-LC classes for Caribbean islands may
underestimate agricultural land uses, and so the influence of that bias on the use of the
data in several ongoing analyses needs to be evaluated (J. Gebelein, L. Burke, and
J. Robinson, unpubl data). Unlike the IGBP classification scheme, which does not
specifically identify coastal wetland types, the Geocover-LC scheme includes a
Wetland/Mangrove class in (Table 2).
3.3.2 Digital elevation models (SRTM)
The Shuttle Radar Topography (SRTM) mission flown in February 2000 collected
radar interferometry data over 80% of the world’s landcover (Werner, 2001). Data are
still being processed and new digital elevation models (DEMs) are gradually being
released through 2004 (Rabus et al., 2003). C-band (5.6 cm wavelength) synthetic
aperture radar (SAR) data are processed by the NASA Jet Propulsion Laboratory, and
products are distributed by the USGS (U.S. Geological Survey) Eros Data Center. Two
near-global products are available for public release: 1-arc second (30 meter) SRTM
data postings of the continental United States and 3-arc second (90 meter) international
continental datasets (Farr and Kobrick, 2000). Data processing and public release is
scheduled to be complete in 2005. Versions of standard topographic data (such as the
U.S. Geological Survey GTOPO30) are also being updated based on new SRTM
data. X-band interferometric SAR data will be processed by the German Remote
Sensing Data Center of the German Aerospace Center (DLR). X-band has nearly twice
the accuracy in measuring elevations, but a narrower swath width leaves gaps in
coverage (Bamler, 1999). Nearly global 30 m data will be available from the DLR
(http://www.eoweb.dlr.de) at cost of archiving and distribution (Werner, 2001).
292
Robinson, Andréfouët and Burke
The Earth Satellite Corporation (EarthSat) contracted with the NASA in 1998 to
generate an orthorectified satellite image base (Tucker et al., 2004), and then contracted
with the National Imagery and Mapping Agency (NIMA) to produce a land cover map
of the earth’s landmasses. The GeoCover-LC product (Earth Satellite Corporation
2003) is the first moderate resolution land cover map of the world using Landsat
Enhanced Thematic Mapper (ETM+) and Thematic Mapper (TM) data. EarthSat used
a proprietary process to generate orthorectified tiles of ETM+ data for the Earth’s
landmasses with a 1.4 ha minimum mapping unit (accuracy equivalent to 1:200,000scale maps). The first set of maps was generated utilizing 1990 imagery and covers
North America and the Caribbean, Africa, Europe and east Asia. The second using
2000 data covers non-Amazonian South America, central and southeast Asia. Both
datasets consist of a 13-class land cover legend. Updated coverages for northern
Africa, Europe and east Asia were produced using 2000 data and a patented “Cross
Correlation Analysis.” This method detects change between the 1990 Landsat 4/5
images and the 2000 Landsat 7 images. The full Geocover classification is then
reconstructed from the older data and the changed data for the update. Although the
coverage was originally envisioned to be global, land cover has not been mapped for
Australia, New Zealand, the Amazon, and parts of northern Eurasia. Because it was
produced by a commercial entity, Geocover-LC products must be obtained under
license.
The Geocover-LC scheme has an uncertain degree of validation, and studies that
make use of the data in synthesis applications need to validate its use. For example,
some preliminary data indicates that Geocover-LC classes for Caribbean islands may
underestimate agricultural land uses, and so the influence of that bias on the use of the
data in several ongoing analyses needs to be evaluated (J. Gebelein, L. Burke, and
J. Robinson, unpubl data). Unlike the IGBP classification scheme, which does not
specifically identify coastal wetland types, the Geocover-LC scheme includes a
Wetland/Mangrove class in (Table 2).
3.3.2 Digital elevation models (SRTM)
The Shuttle Radar Topography (SRTM) mission flown in February 2000 collected
radar interferometry data over 80% of the world’s landcover (Werner, 2001). Data are
still being processed and new digital elevation models (DEMs) are gradually being
released through 2004 (Rabus et al., 2003). C-band (5.6 cm wavelength) synthetic
aperture radar (SAR) data are processed by the NASA Jet Propulsion Laboratory, and
products are distributed by the USGS (U.S. Geological Survey) Eros Data Center. Two
near-global products are available for public release: 1-arc second (30 meter) SRTM
data postings of the continental United States and 3-arc second (90 meter) international
continental datasets (Farr and Kobrick, 2000). Data processing and public release is
scheduled to be complete in 2005. Versions of standard topographic data (such as the
U.S. Geological Survey GTOPO30) are also being updated based on new SRTM
data. X-band interferometric SAR data will be processed by the German Remote
Sensing Data Center of the German Aerospace Center (DLR). X-band has nearly twice
the accuracy in measuring elevations, but a narrower swath width leaves gaps in
coverage (Bamler, 1999). Nearly global 30 m data will be available from the DLR
(http://www.eoweb.dlr.de) at cost of archiving and distribution (Werner, 2001).
292
Robinson, Andréfouët and Burke