Remote Sensing : Visible
Satellite view of sea ice breaking up in the Beaufort Sea off Alaska, 15 April 2004. The top half of the image with several dark lines is the sea ice, and the solid white object is the coast of Alaska with a fringe of fast ice. This visible image was captured from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on NASA's Terra satellite.
—Image courtesy of MODIS Rapid Response Project at NASA/GSFC.
Satellite view of sea ice (white area in center of image) in Hudson Bay (dark blue). The green area is Canada. This image was captured on 22 June 2000 by the SeaWiFS sensor on the OrbView-2 satellite and shows that the northern half of Hudson Bay thawed before the southern half.
—Image provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE.
The light that our eyes detects is visible radiation from the sun, reflected off objects around us. "Whiter" objects (those with a high albedo) reflect more radiation than "darker" objects. Sea ice has a higher albedo than the surrounding ocean, which makes it easy to detect from visible remote sensing instruments. Some limitations in using reflected visible light to observe sea ice from space include the following:
Since these sensors measure reflected radiation from the sun, visible data can only be collected during the daytime. The inability to measure at night is a problem for measuring sea ice, which exists in polar regions where darkness prevails.
Because clouds also reflect visible radiation, a cloudy sky prevents satellites from viewing visible light reflected from sea ice. Unfortunately, ice-covered polar regions tend to be cloudy, with clouds obscuring sea ice 70 to 90 percent of the time.
The following satellites and sensors are a selection of those that observe vislble radiation; these are often used to identify and map sea ice.
The Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS)
The National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR)
The National Aeronautics and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS)