Nighttime Imaging Grows Landsat’s Science Value

By Earth Resources Observation and Science (EROS) Center For more than 50 years, Landsat has imaged Earth’s land and near-shore surfaces as the satellites descend in midmorning orbit, when daily sunlight is optimal. That’s just what they’ve always done. Currently, Landsat 8 and Landsat 9 circle the globe while also making better use of their ascending paths, peering into the darkness for special requests. The visible spectral bands of Landsat—the same blue, green and red wavelength colors our eyes can see—are typically not that useful when collected on the ascending orbit node (also known as “nighttime imagery”). The exception is twilight or darkness at Earth’s poles, which can provide a surprisingly clear observation in the thermal infrared spectral bands where snow, ice and water temperatures can be retrieved when the sun is at or below the horizon. Through the dark, shortwave infrared (SWIR) bands within Landsat’s Operational Land Imager (OLI) instrument can detect intense heat sources such as volcanoes or active fires, while the Thermal Infrared Sensor (TIRS) measures surface temperatures that range from geothermal geysers to solid ice. There is a growing interest in seeing what Landsat can capture as it ascends over the dark side of Earth, according to Dr. Christopher Crawford, the Landsat Project Scientist at the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center. …