Colvocoresses Reef
Encyclopedia
Colvocoresses Reef is a wholly submerged atoll
structure in the Northeast of the Chagos Archipelago
, Indian Ocean
. It is located 15 km east of Speakers Bank
and 28 km northeast of Blenheim Reef
. The reef measures 8 km north-south, and is 1 to 2 km wide, with a total area of about 10 km². Breakers
are visible only during heavy seas.
who developed in 1973 - 1979 the Space-oblique Mercator projection
with John P. Snyder
and John L. Junkins. The least charted depth is 9 meters deep above the reef. This sounding was one of only a few that were ever incorporated into US nautical chart
s, having been derived not from sonar or lead line data, but from radiometric data from the Landsat Multispectral Scanner
(MSS
) imagery.
Colvocoresses Reef is unique in that it was discovered by use of images taken by the National Aeronautics and Space Administration's (NASA) Landsat Satellite. The Landsat MSS 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. Although the red band penetrates clear water to only about eight meters, the green band has been proven to see through clear ocean waters to depths of about 30-40 meters. Since light is exponentially attenuated through the water column, given clear water and similar bottom reflectances, deeper water will appear darker on the Landsat images.
The original depth data for the shallow water areas on Chagos Archipelago nautical charts had been collected in the mid-1830s. Except for the areas around Diego Garcia
, the 1830's data is still shown on the current chart. 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 edition of the Chagos Archipelago nautical chart (#61610) 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.
a probable depth range for the reef with a caution on the chart that there were probably shallower features on the reef.
Atoll
An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...
structure in the Northeast of the Chagos Archipelago
Chagos Archipelago
The Chagos Archipelago , is a group of seven atolls comprising more than 60 individual tropical islands in the Indian Ocean; situated some due south of the Maldives archipelago. This chain of islands are the southernmost archipelago of the Chagos-Laccadive Ridge a long submarine mountain range...
, Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
. It is located 15 km east of Speakers Bank
Speakers Bank
Speakers Bank is a large coral atoll structure in the Northwestern part of the Chagos Archipelago. It is the northernmost feature of the archipelago, located at , 22 km Northwest of Blenheim Reef and is 44 km Northeast-Southwest, and 24 km wide. The total area is 582 2, mostly water....
and 28 km northeast of Blenheim Reef
Blenheim Reef
Blenheim Reef is a partly submerged atoll structure in the Chagos Archipelago, Indian Ocean]]. It includes the coral reef of Baxio Predassa in its southeastern rim, plus another completely submerged part. It is located in the northeastern part of the Chagos Archipelago...
. The reef measures 8 km north-south, and is 1 to 2 km wide, with a total area of about 10 km². Breakers
Breaker (reef)
A breaker is a piece of reef against which waves break.This sense of the term is closely related to another sense, that of the breaking wave itself. In times past, when ocean navigation was relatively rudimentary, a line of breaking waves was a crucial indicator that a boat was bearing down upon an...
are visible only during heavy seas.
History
This submerged atoll is named after Dr. Alden Partridge ColvocoressesAlden Partridge Colvocoresses
Colonel Alden Partridge Colvocoresses , USA , developed in 1973 - 1979 the Space-oblique Mercator projection with John Parr Snyder and John L. Junkins...
who developed in 1973 - 1979 the Space-oblique Mercator projection
Space-oblique Mercator projection
Space-oblique Mercator projection is a map projection.-History:The space-oblique Mercator projection was developed by John P. Snyder, Alden Partridge Colvocoresses and John L. Junkins in 1976. Snyder had an interest in maps, originating back to his childhood and he regularly attended cartography...
with John P. Snyder
John P. Snyder
John Parr Snyder was an American cartographer most known for his work on map projections for the United States Geological Survey . Educated at Purdue and MIT as a chemical engineer, he had a lifetime interest in map projections as a hobby, but found the calculations tedious without the benefit of...
and John L. Junkins. The least charted depth is 9 meters deep above the reef. This sounding was one of only a few that were ever incorporated into US nautical chart
Nautical chart
A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land , natural features of the seabed, details of the coastline, navigational hazards, locations of natural and man-made aids...
s, having been derived not from sonar or lead line data, but from radiometric data from the Landsat Multispectral Scanner
Multispectral Scanner
The Multispectral Scanner is one of the Earth observing sensors introduced in the Landsat program. A Multispectral Scanner was placed aboard each of the first five Landsat satellites.-MSS Technical Specifications:...
(MSS
MSS
MSS may refer to:Medicine* Marshall-Smith syndrome* Musculoskeletal system* Medical Student SyndromePlaces* Massena International Airport, an airport in Massena, New York* Moses Gate railway station, England; National Rail station code MSS....
) imagery.
Colvocoresses Reef is unique in that it was discovered by use of images taken by the National Aeronautics and Space Administration's (NASA) Landsat Satellite. The Landsat MSS 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
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
bands for sensing plant vigor. These bands have very limited water penetration. Landsat also has two visible wavelength bands: red and green. Although the red band penetrates clear water to only about eight meters, the green band has been proven to see through clear ocean waters to depths of about 30-40 meters. Since light is exponentially attenuated through the water column, given clear water and similar bottom reflectances, deeper water will appear darker on the Landsat images.
The original depth data for the shallow water areas on Chagos Archipelago nautical charts had been collected in the mid-1830s. Except for the areas around Diego Garcia
Diego Garcia
Diego Garcia is a tropical, footprint-shaped coral atoll located south of the equator in the central Indian Ocean at 7 degrees, 26 minutes south latitude. It is part of the British Indian Ocean Territory [BIOT] and is positioned at 72°23' east longitude....
, the 1830's data is still shown on the current chart. In 1975, the Defense Mapping Agency's Hydrographic Center
Hydrographic office
A hydrographic office is an organization which is devoted to acquiring and publishing hydrographic information.Historically, the main tasks of hydrographic offices were the conduction of hydrographic surveys and the publication of nautical charts...
, subsequently incorporated into the National Geospatial-Intelligence Agency
National Geospatial-Intelligence Agency
The National Geospatial-Intelligence Agency is an agency of the federal government of the United States with the primary mission of collecting, analyzing and distributing geospatial intelligence in support of national security. NGA was formerly known as the National Imagery and Mapping 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 edition of the Chagos Archipelago nautical chart (#61610) 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.
Notice to mariners
The brightness of the reef was compared with the brightness of other reefs that had known depths and similar bottom reflections. It was deemed advisable to give in a notice to marinersNotice to Mariners
A notice to mariners advises mariners of important matters affecting navigational safety, including new hydrographic information, changes in channels and aids to navigation, and other important data.Over 60 countries which produce nautical charts also...
a probable depth range for the reef with a caution on the chart that there were probably shallower features on the reef.