Fringe Correction for USNO 61" CCD Images
Abstract
A significant source of noise in long wavelength optical images are atmospheric emission lines, particularly from atmospheric O and OH molecules. CCD detectors often display a complex pattern known as \fringes" that arises due to these telluric night-sky emission lines produced in Earth's atmosphere. These emission lines undergo multiple internal reflections within the silicon detector leading to constructive and destructive interference. Variations in the thickness of the silicon layer produce a complex wood-grain-like pattern across images. Fringing begins to be an issue for CCDs when the absorption depth within the silicon becomes comparable with the thickness of the CCD, which generally occurs at red-optical wavelengths. Further, because the strength of the telluric lines can depend on atmospheric conditions, the amplitude of the fringe pattern can be variable in a given night. We describe below a fringe mitigation technique designed to work with and tested on z-band images from the 61"Kaj Strand Telescope at the US Naval Observatory Flagstaff Station. We note here that fringe patterns and mitigation techniques are very likely instrument, telescope, and site-specific. Therefore, while the process described below was found to have satisfactory results for these specific images, this strategy may not be applicable to other observations.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 08, 2021
- Accession Number
- AD1152315
Entities
People
- Adam C. Schneider
- Frederick J. Vrba
Organizations
- United States Naval Observatory