Status Report

NASA MODIS Image of the Day: November 21, 2010 – Railroad Valley

By SpaceRef Editor
November 21, 2010
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NASA MODIS Image of the Day: November 21, 2010 – Railroad Valley
NASA MODIS Image of the Day: November 21, 2010 - Railroad Valley


Mid-autumn snow covered the high mountain peaks of the southwestern United States on November 12, 2010 when the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite passed over the region, capturing this true-color image.

In the west, on the border of California and Nevada, lie the green Sierra Nevada Mountains.

In the north of the image, just east of the Great Salt Lake, the Wasatch Range runs north to south. This Range forms the western edge of the Rocky Mountains and marks the eastern edge of the Great Basin. Near the center of the image, just south of the snow-spattered mountain ridges of central Nevada, lies a salt playa within Railroad Valley. The dry lakebed is 1,350 m above sea level and is a desert site with no vegetation. This site plays a special role for MODIS and other satellite instruments, because it is one area used for “vicarious calibration” of instruments. In order to make sure remote sensing instruments deliver reliable data, they must be calibrated, which means their measurements are checked against an accurate standard. Before launch, this can be done directly, using standard equipment and techniques on the ground. Once launched, techniques that make use of natural or artificial sites on the surface of the Earth can be used to calibrate the instruments. This is called “vicarious calibration”. In this technique, the instrument undergoing calibration takes measurements at nearly the same time (same conditions) as a known accurate instrument takes the same measurements, and results are compared. The accuracy of vicarious calibration over land depends on the choice of an appropriate calibration target. Ideally, such a calibration site should be flat, bright, spatially uniform, spectrally stable over time, and sufficiently large. Desert playas are preferred for vicarious calibration of moderate spatial resolution sensors due to their optical properties, predictably sunny conditions and low atmospheric aerosol loading.

SpaceRef staff editor.