Paul Kervin (Air Force Research Laboratory/RDSMA), Doyle Hall (Boeing LTS), Mark Bolden (Air Force Research Laboratory/RDSMA), Joe Toth (Boeing LTS)
Keywords: Non-Resolved Object Characterization
Abstract:
The concept of phase angle as a variable of interest when reporting resident space object (RSO) brightness information is widespread throughout the community. Phase angle is the angle between the direction to the Sun and the direction to the observer, as seen at the object being observed. If the object were the Moon, a near-zero degree phase angle would be full moon. Phase angle is widely used in the astronomical community, and has been adopted by the satellite community as well. Phase angle is very useful for some objects (e.g., spherical objects with Lambertian reflectance properties), but rapidly loses its utility when applied to objects which have different properties. It takes four angles to describe the illumination and observing conditions for any RSO observation, two angles describing the direction to the illumination source, and two angles describing the direction to the observer. Replacing those four angles with a single angle, the phase angle, yields an inherent loss of information. For RSOs with complex structures, or whose orientation with respect to the Sun and the observer changes with time, the correlation of brightness with phase angle is poor. This presentation will discuss phase angle, how correlations with phase angle break down for most RSOs, and discuss under what conditions phase angle is a useful parameter, and under what conditions it is not.
Date of Conference: September 14-17, 2010
Track: Non-resolved Object Characterization