21 July 2010 Detection of a geostationary satellite with the Navy Prototype Optical Interferometer
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Abstract
We have detected a satellite via optical interferometry for the first time, using a 16 m baseline of the Navy Prototype Optical Interferometer (NPOI) to observe the geostationary communications satellite DirecTV-9S during the "glint" seasons of February-March 2008 and 2009 when the sun-satellite-NPOI geometry was favorable for causing specular reflections from geostationary satellites. We used the US Naval Observatory Flagstaff Station 1 m telescope to generate accurate positions for steering the NPOI. Stars are the easiest targets for optical/infrared interferometers because of their high surface brightness. Low surface brightness targets are more difficult: if they are small enough not to be resolved out by typical baselines, they are likely to be too faint to produce detectable fringes in an atmospheric coherence time. The 16 m NPOI baseline, the shortest available at the time of our observations, resolves out structures larger than ~ 1.5 m at the geostationary distance, while a typical size for the solar panel arrays is 2 m x 30 m. Our detection indicates that a small fraction of the satellite glinted, not surprising given that the solar panels are not accurately flat. Our fringe data are consistent with a two-component image consisting of a 1 to 1.3 m higher surface brightness component and a significantly larger lower surface brightness component. The brightness of the glints (2.m 4 and ~ 1.m 5 for the two detections in March 2009) and the size scale suggest that the compact component has an albedo of 0.06 to 0.13, while the larger-scale component is much darker, if circular geometry is assumed.
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J. T. Armstrong, J. T. Armstrong, R. B. Hindsley, R. B. Hindsley, H. R. Schmitt, H. R. Schmitt, F. J. Vrba, F. J. Vrba, J. A. Benson, J. A. Benson, D. J. Hutter, D. J. Hutter, R. T. Zavala, R. T. Zavala, } "Detection of a geostationary satellite with the Navy Prototype Optical Interferometer", Proc. SPIE 7734, Optical and Infrared Interferometry II, 77343C (21 July 2010); doi: 10.1117/12.858283; https://doi.org/10.1117/12.858283
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