Project

General

Profile

Sig-R3

Sky brightness in grizy during nights at different moon phases and moon separations are within 0.1 mag of expectations [DECam TG-13]. These specifications are available from docdb #6123

Prerequisites

  • Photometric data obtained during commissioning and SV
  • Information about moon phase, separation, and ideally the full list of parameters provided on the SignalsNoise_Resource_Needs page.

Measure the sky brightness as a function of moon phase, moon separation, and perhaps other parameters for each filter.

Procedure

  • Measure the sky brightness in images that sample a useful range of moon phase, moon separation, and potentially other quantities. Lots of codes exist that can measure the mean sky brightness in an image.
  • Request specific observations as needed to insure certain moon phases and angles are appropriately sampled.
  • A spreadsheet or database will need to be maintained throughout the SV period with all of these quantities and measurements. The sampling of these quantities will need to be reviewed at least every few nights.

Analysis

Analysis relevant to this requirement is available on this wiki page: Sky Brightness Measurements

Verdict

Compare sky brightness measurements to expectations.

Consequences

If the sky brightness is higher than the assumptions used to generate the survey, investigate the implications of modifications of survey design parameters.

Result: Passed

The sky brightness was measured at numerous points during the SV period and these measurements indicated that the dark sky was as dark or darker than expectations (note this was only for griz, as Y was not in the model). The wiki page on Sky Brightness Measurements has several tables of measurements, as well as numerous diagnostic plots. These data also exhibit reasonable agreement with Eric Neilsen's sky model. A long term goal is to refit the model to data obtained during the SV period, in particular with respect to moon separation, but that is not needed to meet this requirement.

Other Notes

Some information on stray light tests are part of the DECam Commissioning Calibration Testing Plan Detailed Checklist (docdb#6449)