Wednesday, October 03, 2007

A Night Time Gage for Global Warming

Land surface temperature is a good indicator of the energy balance at the Earth's surface, and serves as an important indicator of the greenhouse effect. Land surface temperature can be used for evaluating water requirements of crops, for determining frost-damaged areas in orange groves, and for assessing the impact of climate change on the Arctic, an environment that will be particularly sensitive to rising global temperatures.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites take the temperature of every square kilometer of the Earth nearly every day, barring cloudy skies. MODIS senses the temperature of all natural and man-made land surfaces —everything from snow to deserts, from rooftops to treetops. The map above shows nighttime LST ending a six year cycle from March 2000 to July 2006. An animated seq can be generated here. Values range from 250 to 320 Kelvin (about -23 to 47 degrees Celsius, or -10 to 116 degrees Fahrenheit) in shades from light to yellow.

Nighttime LST measurements have an interesting land-cover mapping application. Manmade surfaces such as concrete and asphalt that dominate cities typically absorb a lot more heat than the natural land cover that surrounds them. Having soaked up heat all day long, cities stay warmer at night than their surrounding natural areas, and so they stand out as warm spots. This phenomenon has come to be called "the urban heat island effect," and scientists can study urban sprawl by using nighttime LST data like that from MODIS.

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