Colvocoresses Reef

Colvocoresses Reef is a wholly submerged atoll structure in the Northeast of the Chagos Archipelago, 15 km East of Speakers Bank and 28 km Northeast of Blenheim Reef. It is named after Dr. Alden Partridge Colvocoresses who developed in 1973 - 1979 the Space-oblique Mercator projection with John Parr Snyder and John L. Junkins. The least charted depth is 9 meters deep above the reef. Breakers are visible only during heavy seas. The reef measures 8 km north-south, and is 1 to 2 km wide [1], with a total area of about 10 km².

Colvocoresses Reef is unique in that it is was discovered by use of images taken by the National Aeronautics and Space Administration's (NASA) Landsat Satellite. The Landsat images the earth with several spectral bands. Each band provides a black and white image that is taken through a spectral filter. It has two non-thermal infrared bands for sensing plant vigor. These bands have very limited water penetration. Landsat also has two visible wavelength bands: red and green. The green band has been proven to see through clear ocean waters to depths of about 30-40 meters.

In 1975, the Defense Mapping Agency's Hydrographic Center, subsequently incorporated into the National Geospatial-Intelligence Agency (NGA), requested NASA to collect Landsat images over the Chagos Archipelago. The images revealed the previously uncharted Colvocoresses Reef as well as errors in positioning of numerous other reefs in the Archipelago. Some were out of position by as much as 18 kilometers. By the summer of 1976 a new chart of the Chagos Archipelago was printed showing the corrected positions of the banks and shoals as well as Colvocoresses Reef. This was the first nautical chart known to have been completely revised using the Landsat imagery.