Stray light in EPIC
Abstract
The images taken by the Earth Polychromatic Imaging Camera (EPIC) are affected by spatial stray light. Therefore a stray light correction algorithm, which is based on the knowledge of the instrument's point spread functions (PSF), will be applied on the data. Laboratory measurements to determine the PSF have been made at the Lockheed Martin Advanced Technology Center at flight conditions (vacuum chamber, cooled CCD) and, for initial testing, at room conditions (air pressure, CCD at room temperature). Since the PSF covers a huge dynamic range (8 orders of magnitude), it could only be resolved by combining measurements from sub-pixel size illumination and also more extended beams covering about 1000 of EPIC's 2048x2048 pixels. From tests at room conditions we determined that 50% (90%) of the light from a point source ends inside a circle of diameter 1.6pixels (3pixels). This corresponds to about 13km (23km) at the ground when the instrument is in orbit. While the exact shape of the PSF could not be determined from the tests at room condition, the order of EPIC's spatial stray light could be estimated to ~10%. This means that 10% of the light from a point source spreads over the whole CCD. Without applying a stray light correction, the stray light would cause a systematic underestimation of the signal from bright scenes (areas covered by clouds) by about 8% and a systematic overestimation of the signal from dark scenes (clear sky) ranging from 2% in the 317nm channel to 40% in the 763nm channel.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.A33B0193C
- Keywords:
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- 0394 ATMOSPHERIC COMPOSITION AND STRUCTURE / Instruments and techniques