Satellite Imaging and Characterization with Optical Interferometry

In this paper we discuss the possibility of imaging geostationary satellites with optical interferometers. Geostationary satellites are generally too large to image in a resolved way with conventional single-dish telescopes. However, optical interferometers can be used to increase the angular resolution. Interferometric imaging of satellites is different from the imaging of stars where Earth-rotation synthesis can be employed. Instead it is necessary to combine an interferometer with many baselines with wavelength synthesis, and that produces the ability to make crude images. From the point of view of existing interferometers most geostationary satellites are large targets. That reduces the observed visibility which can make fringe-tracking difficult. We find that a larger aperture (such as are planned for the MROI) under ideal conditions, and assuming the satellite is a perfect diffuse reflects can track fringes on many satellites in the typical range of satellite brightnesses, but that any small deviations, such as non-ideal seeing or imperfect reflection from the satellite, can significantly narrow the number of targets. The equinox glint can help. However, using the equinox glint to track fringes will hurt imaging performance, requiring a much larger increase of the already long integration time. We conclude that, although more detailed modeling is required, imaging geostationary satellites with interferometers may be feasible if large apertures are used, an exceptionally good site is used or the telescopes are equipped with effective adaptive optics, and coherent integration techniques, large (10) number of telescopes, and wavelength synthesis are made use of.