GMI Monitors Earth's Newest, Giant Iceberg
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On July 12, 2017, a giant iceberg broke off Antarctica and a variety of satellites have been used to study it ever since. The Global Precipitation Measurement (GPM) Microwave Imager (GMI) instrument can see the ribbon of relatively warm water and ice that separates the newly formed iceberg from the its parent mass of ice, the Larsen C ice shelf. While the iceberg is separated from the parent iceshelf by only a few kilometers, the GMI instrument is sensitive enough to detect the variation in temperature between this relatively warm gap and the colder ice shelf and iceberg.
The accompanying three images show the three overflights of the iceberg that were made by the GPM satellite on three subsequent days starting on July 12, the day that the iceberg formed. On July 12, the U.S. National Ice Center gave this iceberg the name "Iceberg A-68". Iceberg A-68 is expected to remain roughly in place for now because its mobility is currently limited by hundreds of kilometers of floating sea ice that separate iceberg A-68 from the open sea in the middle of the Antarctic winter.
The GMI instrument contains 13 channels that respond to different frequencies and polarizations of Earth's faint, natural glow in the microwave spectrum. These 13 channels are routinely used to estimate rainfall and snowfall, but these same channels are also sensitive to changes in Earth's cloud cover, humidity, and temperature. In an unusual twist, these same observations can be used to examine the environment of the large iceberg that just formed off Antarctica.
The red, green, and blue intensity of these GMI images are determined by GHI's 89 GHz vertically and horizontally polarized channel and the 37 GHz vertically polarized channel. This method of displaying information from three channels at once builds on the earlier work of NASA scientists Andrew Negri, Robert Adler, and Christian Kummerow, who were working at the time with an earlier generation of satellite-borne passive microwave instruments. Some of the features in the three GMI images were identified using information from the National Snow and Ice Data Center at the University of Colorado, the VIIRS instrument from the Suomi NPP satellite, the MODIS instrument on the Aqua satellite, composite satellite imagery from the Antartic Meteorological Research Center at the University of Wisconsin, and the NASA Earth Observatory Website (https://earthobservatory.nasa.gov).
Realtime GPM data courtesy of NASA / JAXA.
Data visualation by Owen Kelly and Matt Lammers of the NASA Goddard Precipitation Processing System