SignalsNoise Resource Needs

Number/name of Requirement or Goal: Sig R1-4

Sig-R1 (read noise is low) and Sig-R2 (zeropoints are near expectations) we will assume will be done during Commissioning. The zeropoints will be further measured extensively during the SV photometric calibration exercises.

Sig-R3 is to characterize range of sky brightness and dependence on moon phase & distance. A first measure will be done during Commissioning, but during SV we will continue to collect more measures as moon phase changes, and also measure distribution of time-variable airglow-dominated sky backgrounds.

For this purpose it will be useful to accumulate a database of information about every sky exposure during SV:
*date and time
*exposure time
*weather conditions (at least a photometric/nonphotometric flag)
*flag if the data are known to be bad for some reason
*zenith distance
*time relative to astronomical twilight end/start (or sunset/rise)
*moon phase
*moon angle from field
*moon zenith distance

Sig R-4 would involve examining database outputs to make sure that OBSTAC strategies are properly tuned to avoid degradation by bright sky background.

DECam observations

  • Field(s) to observe: Measure sky brightness parasitically on DECam exposures taken during SV
  • Number, duration of exposures per filter: as required by other programs
  • Dithering / tiling pattern: unimportant
  • Sky conditions needed (seeing, photometric, moon phase, etc:): Must make sure that exposures are taken in all bands at all Moon phases during SV, with exploration of moon distance from field too.
  • Other timing constraints:

Data processing needs

Which of the following products would you need to conduct the test:

Only requirement is a measure of sky brightness on each exposure, with zeropoint known to <0.05 mag. SISPI WCS will suffice to determine pixel solid angle.

Telescope or other engineering data

Sky conditions recorded as noted above.

External data sets

Sky brightness levels assumed for DES planning.

Codes and scripts for analysing the test data

*Sky level determination for each image (one chip would suffice).
*Accumulation of SV exposure database as time goes on.
*Analysis of sky brightness vs moon phase / distance, and range/time scale of stochastic variations.


Are there real-time decisions to be made during the observations? No

How quickly can / must the data be available and analysed? 48-hr return of sky brightnesses and crude zeropoint for each exposure.

Who will do it, and where? Analyses can be done off-site.

Other important resources or things to note

Need to construct a simple spreadsheet / database of sky brightness and relevant observational conditions.

Prior to the start of SV, investigate the moon phase distribution relative to the extent of SV to insure that useful calibration data are not missed (e.g. a sky brightness data at a range of distances from the full moon).

Approximately halfway through SV, investigate how well the observations obtained to that point sample what will be needed to characterize background variations. At that point determine if any active scheduling is required.

Access to the same data from the commissioning period would be valuable.