| Summary: | Earth’s energy budget drives its climate. Many satellite radiometers have provided top of atmosphere radiation measurements to estimate the energy budget. We present a first look at previously unpublished measurements of Earth-reflected sunlight from broadband pixelated radiometers in the visible and near-visible wavelength range operating on satellites in the Global Positioning System (GPS) constellation since 2011.The radiometers collect synoptic measurements of Earth-reflected sunlight, including polar region coverage, due to the 55° inclination and 20,200 km altitude of the GPS orbits. We present an initial comparison of these radiometers with the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) on the Meteosat-11 geostationary satellite. We also demonstrate the ability of these radiometers to detect changes in reflected sunlight over time. Specifically, measurements ±40 days around the polar summer solstices show (1) reflected sunlight from the Antarctic south of 80°S is symmetric around the solstice, implying constant reflectance, and (2) reflection from the Arctic north of 80°N is ~20% dimmer than the Antarctic and decreases 20%-35% over 80 days. The variation in the Arctic region indicates these radiometers observe albedo changes related to sea ice melting. GPS-based radiometers could provide an additional method of validating data collected by other optical sensors. The GPS-based radiometer data could also verify the spatial, temporal, and spectral interpolation and extrapolation to the full earth used for data collected by Low Earth Orbiting satellites and fill in coverage gaps between generations of sensors.
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