Abstract
A calibration satellite (CalSat) hosting a convex reflector projecting an image of the sun could serve as a very accurate radiometric source for ground-based and space-based sensors. A half meter reflector orbiting near geo-synchronous orbit could project a V ~ 8 magnitude image over 1000 km diameter region at the surface of the earth. By placing the CalSat slightly below the geosynchronous belt, the apparent position of satellite would slowly advance and, over period of a few months, be observable from nearly everywhere on Earth. The irradiance for a given observer depends specifically on the sun-reflector-observer distances and the radius of curvature of mirror, all parameters that are accurately known. The remaining key parameter is the spectral radiance of the sun. Because the latter is known, or can be measured, more accurately than any other star, this orbiting reflector provides a nearly ideal calibration reference, namely a bright point source whose irradiance over a very broad range of wavelengths is known to better than 1%.
In addition to the basic reflector concept, issues including attitude control, data rates, reflector design and surface monitoring while on orbit will be discussed. This work is supported at The Aerospace Corporation by the Independent Research and Development program.
Absolute Radiometric Calibration Using a Solar Reflector in Near-Geosynchronous Orbit
A calibration satellite (CalSat) hosting a convex reflector projecting an image of the sun could serve as a very accurate radiometric source for ground-based and space-based sensors. A half meter reflector orbiting near geo-synchronous orbit could project a V ~ 8 magnitude image over 1000 km diameter region at the surface of the earth. By placing the CalSat slightly below the geosynchronous belt, the apparent position of satellite would slowly advance and, over period of a few months, be observable from nearly everywhere on Earth. The irradiance for a given observer depends specifically on the sun-reflector-observer distances and the radius of curvature of mirror, all parameters that are accurately known. The remaining key parameter is the spectral radiance of the sun. Because the latter is known, or can be measured, more accurately than any other star, this orbiting reflector provides a nearly ideal calibration reference, namely a bright point source whose irradiance over a very broad range of wavelengths is known to better than 1%.
In addition to the basic reflector concept, issues including attitude control, data rates, reflector design and surface monitoring while on orbit will be discussed. This work is supported at The Aerospace Corporation by the Independent Research and Development program.