Spectral Measurements of Geosynchronous Satellites During Glint Season

Abstract

Operational communication geosynchronous satellites are typically large structures with solar panels that maintain a stable attitude relative to the Earth and Sun. During the equinox periods, the geometry of the satellite, the sun, and an Earth observer is favorable for a condition to occur called a glint, or a specular reflection off the satellite. It is presumed that the glint is caused by the solar panels because those structures are solar oriented. This phenomenon was previously observed and reported using broadband photometry techniques. In this paper, glint observations from two satellites are presented, Wildblue-1 and DirecTV-12, as measured across the visible spectrum using slitless spectroscopy techniques. It is clear from the results that the wavelength where the glint maximum occurs is shifted toward the blue or shorter wavelength end of the spectrum relative to the time periods before and after the glint. It is also clear from the data that the spectral reflectance during the glint is less like a blackbody compared to spectra before and after the glint. This is consistent with the presumption that the solar panels are the main cause of the satellite glint. These results indicate spectral measurements may offer the ability to discern satellite features such as solar panel orientation and relative or potentially absolute power capacity.