In Southern California irrigated farmland stretches north- and southward from the Salton Sea—an artificial inland sea in the desert. Blocks of square farmland appear in shades of green and tan in the natural-color image acquired on March 24, 2013 by the Operational Land Imager onboard the Landsat Data Continuity Mission—now renamed Landsat-8. On that same day, thermal measurements from the Thermal Infrared Sensor (grayscale image) show that the crops had different temperatures—specifically, cooler areas appear as dark shades, while warmer areas appear as bright shades. Dark pixels—representing cooler areas—in thermal images from TIRS help water managers determine where water is being used for irrigation. Plants cool down when they transpire, so the combination of water evaporating from the plants and the ground (i.e., evapotranspiration) lowers the temperature of the irrigated land. Scientists use these thermal measurements to calculate how much water agricultural fields are using.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 18.104.22.168.0