Executive summary

Release content:

All 50 completed (u,g,r,i) tiles observed before 31 September 2012.

Data products:

  • Coadds: photometrically and astrometrically calibrated, stacked images (1 per filter per tile)
  • Weights: weight frames (1 for each Coadd)
  • Flag images: FITS images with pixel flags in areas affected by bright stars, saturated pixels, reflections, and other artefacts (1 for each Coadd)
  • Source lists: lists of sources detected in single Coadds

Data quality:

PSF size and ellipticity distributions and achieved limiting magnitudes can be summarized as follows:

FilterPSF FWHM
(arcsec)		PSF
ellipticity		Limiting mag
(2'' 5σ AB)
u<1.2~0.04~24.3
g<1.0~0.05~25.1
r<0.85~0.05~24.9
i<1.2~0.05~23.7

Photometric calibration:

The photometric calibration is in AB magnitudes in the instrumental photometric calibration. Tiles are photometrically homogenized by tying stellar photometry between the dithers and overlapping CCDs together; the resulting photometry is flat to typically within 2% over the full square degree FOV. Absolute photometry is done per tile and based on nightly zeropoints based on SA field observations.

Astrometric calibration:

Global solutions are calculated for each tile, spanning all dithers and CCDs, with 2MASS used as reference catalog. The 2-dimensional RMS of source positions between the dithers is typically 0.03 arcseconds.

Bright star and defects masking:

Flag images are provided with pixel flags indicating regions affected by saturated pixels, diffraction spikes, reflection halos, and other (manually masked) defects.

Source lists:

Single-band source lists are extracted from the Coadds. The source lists provide for each detected source several magnitude measurements, a large number of aperture fluxes, star/galaxy classification, and masking flags.
The typical 98% completeness magnitudes for the 4 filters are 22.8 in u, 24.0 in g, 23.9 in r, and 22.5 in i.

Data access:

Data products can be accessed via:

Relevant links: