Land Cover Mapping: Africa Completed
While working in Africa, Dr. Alain Gachet of RTI saw a need for new maps of the continent, particularly inland maps. Almost all geological maps of Africa were created during the 1960s before some African countries became independent. The coastal maps are fairly accurate, as they were required to meet the standards of the French, English, and U.S. Navies. Inland maps beyond 50 km from the shore, however, diverge significantly, with geolocation errors of several kilometers.
While working in Africa, Dr. Alain Gachet of RTI saw a need for new maps of the continent, particularly inland maps (written commun., 2013). Almost all geological maps of Africa were created during the 1960s before some African countries became independent. The coastal maps are fairly accurate, as they were required to meet the standards of the French, English, and U.S. Navies. Inland maps beyond 50 km from the shore, however, diverge significantly, with geolocation errors of several kilometers. This is due to the nature of the tools used at the time, such as the astronomic compass (sextant) and the clock. Most topographical maps drawn during this period contain errors up to 22 km on 1:50,000 scale. Such inaccuracies make it very difficult to conduct inland work relating to oil, gas, mineral and water exploration.
Radar Technologies International was able to use Landsat to redraw the geological maps of Africa, the Middle East and Australasia. Landsat imagery, combined with SRTM data, provides an excellent overview of the topography, including drainage and watershed boundaries, with a geolocation accuracy of 10 m. Redrawing new maps with Landsat data enabled RTI, as well as other companies, to use the maps for mineral and oil exploration within those regions.
Figure 1 illustrates the discrepancy between a geologic map drawn in 1972 over a topographic map from 1968 and a Landsat image wrapped on SRTM. The topographic base of the older map is from the U.S. Army Map Service series 2201 Edition 1968. The alluvial layer has been extracted from Landsat and georeferenced on SRTM data from 2004. The basaltic formations are coded in orange in the first map and appear in dark purple in the second. It is hardly possible to recognize the geologic contours drawn in the older map. There is a shift of almost 15 km between the basaltic formations of these two images. Such accuracy is crucial in natural resources exploration: it draws the boundary between the success and failure of an exploration program. Increased accuracy of this type of information also minimizes costs as well as risks, which provide a higher probability of exploration success.
References:
Dr. Alain Gachet, Scientist/Engineer/Owner, Radar Technologies International, France.
Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Back to Technology from 'Landsat Imagery: A Unique Resource'
Case Studies of Landsat Imagery Use
While working in Africa, Dr. Alain Gachet of RTI saw a need for new maps of the continent, particularly inland maps. Almost all geological maps of Africa were created during the 1960s before some African countries became independent. The coastal maps are fairly accurate, as they were required to meet the standards of the French, English, and U.S. Navies. Inland maps beyond 50 km from the shore, however, diverge significantly, with geolocation errors of several kilometers.
While working in Africa, Dr. Alain Gachet of RTI saw a need for new maps of the continent, particularly inland maps (written commun., 2013). Almost all geological maps of Africa were created during the 1960s before some African countries became independent. The coastal maps are fairly accurate, as they were required to meet the standards of the French, English, and U.S. Navies. Inland maps beyond 50 km from the shore, however, diverge significantly, with geolocation errors of several kilometers. This is due to the nature of the tools used at the time, such as the astronomic compass (sextant) and the clock. Most topographical maps drawn during this period contain errors up to 22 km on 1:50,000 scale. Such inaccuracies make it very difficult to conduct inland work relating to oil, gas, mineral and water exploration.
Radar Technologies International was able to use Landsat to redraw the geological maps of Africa, the Middle East and Australasia. Landsat imagery, combined with SRTM data, provides an excellent overview of the topography, including drainage and watershed boundaries, with a geolocation accuracy of 10 m. Redrawing new maps with Landsat data enabled RTI, as well as other companies, to use the maps for mineral and oil exploration within those regions.
Figure 1 illustrates the discrepancy between a geologic map drawn in 1972 over a topographic map from 1968 and a Landsat image wrapped on SRTM. The topographic base of the older map is from the U.S. Army Map Service series 2201 Edition 1968. The alluvial layer has been extracted from Landsat and georeferenced on SRTM data from 2004. The basaltic formations are coded in orange in the first map and appear in dark purple in the second. It is hardly possible to recognize the geologic contours drawn in the older map. There is a shift of almost 15 km between the basaltic formations of these two images. Such accuracy is crucial in natural resources exploration: it draws the boundary between the success and failure of an exploration program. Increased accuracy of this type of information also minimizes costs as well as risks, which provide a higher probability of exploration success.
References:
Dr. Alain Gachet, Scientist/Engineer/Owner, Radar Technologies International, France.
Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Back to Technology from 'Landsat Imagery: A Unique Resource'