By Laura E.P. Rocchio
On public land in the Ivanpah Valley near the California/Nevada border, the world’s largest concentrated solar thermal plant sprawls across the desert landscape. Just on the other side of Interstate 15 (the long straight diagonal line) is the location of a Landsat calibration site.
The thermal solar plant uses more than 170,000 moveable mirrors, or heliostats, to follow the sun and focus the sun’s light on central towers filled with water. The water heats up to ~1000ºF creating steam that drives turbines, thereby creating electricity.
Across the I-15, sun seekers of another sort work. Landsat calibration scientists have long used the large homogenous landscape of Ivanpah’s dry-lake playa to measure sunlight reflected from the surface there. Such field measurements ensure that the true physical radiance of the ground is correctly measured by Landsat satellites. This so-called vicarious calibration helps lock down what the satellite sees to physical ground measurements.
Landsat is known for its rigorously calibrated data—i.e., information that accurately reflects physical conditions of the ground. As Belward and Skøien wrote in an April journal article: “Landsat is currently the only satellite program to provide a consistent, cross-calibrated set of records stretching back over more than four decades, which in turn means the program occupies a key position in the provision of terrestrial essential climate variables.”
While the Ivanpah solar power plant is generally darker than the playa in the visible Landsat channels, occasionally a Landsat 8 OLI detector or two saturates (i.e. the mirrors reflect more sunlight than the detector was made to measure) when it is acquiring data over this area. So calibration scientists may be able to use the solar plant as a special new calibration target.
Further Reading:
+ Harvesting Sunlight in California, NASA’s Earth Observatory
+ Under Construction: The World’s Largest Thermal Solar Plant, an NPR photo collection
+ Landsat’s Ivanpah Playa Radiometric Calibration Site, USGS
