On April 26, 2014 the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite flew over the Amundsen Sea and acquired this thermal image of Iceberg B31. The iceberg is visible as a purple tinted, roughly rectangular object near the center of the image.
This image was acquired from Band 31 on the MODIS instrument. Band 31 is an emissive band, which means it measures energy emitted from the Earth’s surface, rather than reflected light. Temperature affects the amount of energy emitted from the Earth, so Band 31 can detect differences in surface temperature. This is especially useful in the winter months in Antarctica, when light dims and the bands measuring light reflectance have difficulty.
By late April, the darkness of winter had begun to shroud the Amundsen Sea, making clear, photo-like images from true-color bands (4,3,1) no longer available. This thermal image successfully shows the iceberg and separates it from liquid water, sea ice, other icebergs, land ice and clouds.
In this image, the darkest colors, beginning with deep, dark purple, are coldest while warmer temperatures are increasingly light. Freshwater ice, such as Iceberg B31, other icebergs and land ice appear bright purple. Thin sea ice that has just started to form is colder and appears darker purple. Clouds are lighter purple to pinkish.
Iceberg B31 broke off of Pine Island Glacier in November, 2013 and has slowly been drifting from Pine Island Bay. On May 2, 2014 the U.S. National Snow and Ice Data Center estimated B31’s size as about 21 mi x 12.6 mi (34 km x 20 km) – still roughly the size as when it first calved. On that same date, the location was estimated at 72°30’ S and 107°22’ W, which is only 30 miles from its location on March 14 (72°42’S and 108°39’W).