EDRplus and EDR Release - February 10th 2006
The EDR and EDRplus
data products are described in the UKIDSS Early
Data Release paper. The EDR provides a small sample dataset
(about 1% of the whole of UKIDSS) that is representative of the
quality of future survey releases. In addition the EDRplus dataset
contains data of similar quality but where the full filter complement
of a particular survey is unavailable.
The charts linked below reflect the status of the UKIDSS surveys in the
UKIDSS EDRplus release. A description of
the data and how it is held in the archive is given in the
Particular attention should be given to the following notes
detailing limitations and bugs (see also generic issues and bugs noted under
- Co-averaging of the deep stacks in the DXS is subject to digital
quantisation noise because the standard pipeline processing software
uses integer representation of pixel ADUs. Sky noise estimation at the
catalogue extraction stage is also affected by this, and the knock-on
effect is that the deep stack images and catalogues in the DXS are not
optimal in terms of depth. This problem does not affected the UDS deep
stacks, because these were co-added and use floating point representation
for the pixel ADUs.
- For the UDS deep stacks, weight images were converted to confidence
images and the scaling was done independently for each of four overlapping
sub-images created from a single, large mosaic. These independently
scaled confidence images lead to an overestimation in the noise
of around 20%, hence the UDS catalogue error attributes are overestimated
by a similar amount.
- The catalogues produced from the overlapping UDS frames have not been
correctly seamed, so there are unflagged duplicate images in the UDS
source catalogues. FIXED: 15 FEB 2006
- Science-verification data from the DXS has been included in the EDR.
Unfortunately, at the source merging stage the science verification stacks
were not included, so the DXS merged source catalogue does not contain
merged sources for all available fields. FIXED: 15 FEB 2006
- Incomplete JK frame sets in the DXS have not been purged in the
EDR subset, so the EDR and EDRPLUS datasets are identical for the DXS. FIXED: 15 FEB 2006
RELEASE MODIFICATION HISTORY:
- In creating the EDR, all frame sets having incomplete filter coverage
have been removed (they remain in the EDRPLUS). This applies to all
stack image, single-passband catalogue detections derived from them and
merged source data.
Note however that the ancestor images of these stacks (e.g.
normal and interleaved frames and their corresponding confidence images)
still remain in the EDR database.
- There are a variety of image defects in the pixel data that may give
rise to spurious catalogue detections with unusual colours. These result
from, amongst other things, cross-talk images and persistence images
(see Dye et al. for
August 23rd 2006 UDS catalogues removed from the EDR and EDRPLUS
databases since they are highly sub-optimal, and are superseded anyway by
the newly available DR1
WFAU, Institute for Astronomy,
Royal Observatory, Blackford Hill
Edinburgh, EH9 3HJ, UK