Journal Article

Ubercalibration of the Deep Lens Survey

D. Wittman, R. Ryan and P. Thorman

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 421, issue 3, pages 2251-2263
Published in print April 2012 | ISSN: 0035-8711
Published online April 2012 | e-ISSN: 1365-2966 | DOI:
Ubercalibration of the Deep Lens Survey

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We describe the internal photometric calibration of the Deep Lens Survey, which consists of five widely separated fields observed by two different observatories. Adopting the global linear least-squares (‘ubercal’) approach developed for the Sloan Digital Sky Survey (SDSS), we derive flat-field corrections for all observing runs, which indicate that the original sky flats were non-uniform by up to 0.13 mag peak-to-valley in z band, and by up to half of that amount in BVR. We show that the application of these corrections reduces spatial non-uniformities in corrected exposures to the 0.01–0.02 mag level. We conclude with some lessons learned in applying ubercal to a survey structured very differently from SDSS, with isolated fields, multiple observatories and shift-and-stare rather than drift-scan imaging. Although the size of the error caused by using sky or dome flats is instrument and wavelength dependent, users of wide-field cameras should not assume that it is small. Pipeline developers should facilitate routine application of this procedure, and surveys should include it in their plans from the outset.

Keywords: methods: statistical; techniques: photometric; surveys

Journal Article.  11579 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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