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Earth from Space

Pearl and Hermes Reef, Hawaii

IMAGE:  Pearl and Hermes Reef, Hawaii

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Looking out the window of the International Space Station, astronauts often take the time to admire and photograph tropical islands and coral reefs. From an altitude of 400 kilometers and with only a digital camera as a tool, it seems impossible to make detailed measurements of the depth of underwater features. However, a new technique developed by National Oceanic and Atmospheric Administration (NOAA) scientists has done just that -- plotted the depths of lagoon features at Pearl and Hermes Reef, northwest Hawaii, using digital astronaut photography from the ISS.

Measuring water depth is an important step in mapping coral reef environments. Even though digital cameras are designed to visually approximate film photographs, the information they collect is similar to the bands of different wavelengths of light collected by multispectral instruments on satellites. NOAA scientists developed an algorithm that could estimate bathymetry from the blue and green bands in IKONOS satellite data. After calibrating the astronaut photography to the signal in the IKONOS data, the same algorithm could be successfully used with the blue and green channels in the astronaut photography. An accuracy assessment of the bathymetry map shows good correspondence between reference data, IKONOS, and ISS data.

Astronaut photograph ISS005-E-13929 was provided by the Earth Sciences and Image Analysis Laboratory at Johnson Space Center. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.

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Curator: Kim Dismukes
Responsible NASA Official: John Ira Petty

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