The main goal of the T0007 release versus the T0006 release was to improve the absolute and internal photometric calibration of the survey. This has been done by applying recipes adopted by the Supernova Legacy Survey (SNLS) for the SNLS/Deep fields to both the Deep and Wide fields of the CFHTLS. These recipes were used to generate a new set of photometric flat-fields (known as “Elixir B5/SNLS”) which have been used to run a new pre-processing by Elixir at CFHT on the entire CFHTLS raw data set. Consequently, all individual weight-maps and object catalogues have been re-generated at Terapix for T0007.
A new series of shallow photometric calibration observations (a MegaCam program called “L99”) were made in photometric conditions towards the end of the CFHTLS survey. These observations pave in each filter the whole of the CFHTLS Wide within a short time window and are bracketed by observations of the SNLS tertiary standards on the Deep survey fields. These observations allowed the SNLS tertiary standards to be transfered to both the Deep and Wide surveys. This brings the absolute and relative photometric calibration over the entire survey at the 1% level or better in the g,r,i bands, 1.5% in the z band, and at the 2% level in the u* band.
Several other key aspects of the processing have been revised and improved for T0007:
Taken together, these changes represent a significant improvement in the scientific potential of the worldwide release T0007 (2012) compared to the six previous Terapix releases (2004-2009).