SWIR Hemispherical Air-Glow Plotting System SHAPS: Postprint
AIR FORCE RESEARCH LAB KIRTLAND AFB NM
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It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere approximately 85km altitude produces a significant amount of night time radiation in the short wave infra-red SWIR band of wave length 0.9 to 1.7 microns. Numerous studies of these phenomena have demonstrated that the irradiance shows significant temporal and spatial variations in the night sky. Changes in weather patterns, seasons, sun angle, moonlight, etc. have the propensity to alter the SWIR air glow irradiance pattern. By performing multiple SWIR measurements, a mosaic representation of the celestial hemisphere was constructed and used to investigate these variations over time and space. The experimental setup consisted of two sensors, an InGaAs SWIR detector and a visible astronomical camera, co-located and bore sighted on an AZ-EL gimbal. This gimbal was programmed to view most of the sky using forty five discrete azimuth and elevation locations. The dwell time at each location was 30 seconds with a total cycle time of less than 30 minutes. The visible astronomical camera collected image data simultaneous with the SWIR camera in order to distinguish SWIR patterns from clouds. Data was reduced though batch processing producing polar representations of the night sky irradiance as a function of azimuth, elevation, and time. These spatio-temporal variations in the irradiance, both short and long term, can be used to validate and calibrate physical models of atmospheric chemistry and turbulence. In this paper we describe our experimental setup and present some results of our measurements made over several months in a rural marine environment on the Islands of Kauai and Maui Hawaii.
- Atmospheric Physics