SWIR Air Glow Mapping of the Night Sky: Postprint

摘要

It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (approx. 85 km altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band between 0.9 and 1.7 microns wave length. Numerous studies of these phenomena have demonstrated that the irradiance shows significant temporal and spatial variations. 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 can be constructed and used to investigate the variations over time and space. The experimental setup consists of two sensors, one a InGaAs SWIR detector and the other a visible astronomical camera, co-located and bore sighted on an AZ-EL gimbal. This gimbal is programmed to view 45 descrete azimuth and elevation locations which cover the entire sky. The dwell time at each location is 30 seconds with a total cycle time of 30 minutes. The visible astronomical camera collects image data simultaneous with the SWIR. The contrast between the two simultaneous images can be used for cloud detection. Data is reduced through batch processing to produces polar representations of the sky radiance as a function of azimuth, elevation and time. The resulting spatio-temporal variations in the radiance are used in conjunction with physical models of atmospheric chemistry and turbulence. The short term variations over a night as well as the long term variation over a season can be used to validate and calibrate these models. In this paper we present results of our measurements made over a several month period both in the semi-urban desert near Albuquerque New Mexico, and in a rural marine environment on the Islands of Kauai and Maui Hawaii.