[an error occurred while processing this directive]
CFHT Science Data Archive
If you have used the Canadian Astronomy Data Centre (CADC)
for your research, please include the following acknowledgment:
This research used the facilities of the Canadian Astronomy Data Centreoperated by the
National Research Council of Canada with the support of the Canadian Space Agency.
 CADC
 Target: CADC Advanced Search
Register  Contact 
>PI Tools>Queries>CFHTLS>Environment>Help

MegaPrime Phase I Data Products

Introduction

MegaPrime Phase I data products fall into five types:

  1. Raw science images
  2. Raw calibration images
  3. Master calibration ("detrend") images
  4. Processed ("detrended") science images
  5. Meta-Data
Types (3) and (4) are produced by CFHT using the Elixir processing system and then sent to CADC. All five types of data products can be accessed and retrieved through CADC.

All MegaPrime images distributed by CADC have been CFITSIO-compressed.

TERAPIX data products will be included in Phase II.

Details on MegaPrime data specifications and exchange protocols between CFHT, CADC and TERAPIX can be found in the MegaPrime Interface Control Document.

Basic Product Description

  1. Raw science images

    These include all exposures on the sky taken as part of scheduled science programs. Dataset names for raw science images are of the form %do where %d is the exposure number. Example: 688127o. Raw science images can be accessed through the CFHTLS science observation form.

  2. Raw calibration images

    These include all bias, dark current, dome and twilight flat-field images taken as part of standard queue scheduled operations. Dataset names for raw calibration images are of the form %d%c where %d is the exposure number, and %c is a single character indicating the type of calibration (b = bias, d = dark and f = flat-field). Example: 688151b. Raw calibration images can be directly accessed through the CFHT MegaPrime Catalog form. Raw calibration images associated with particular science images can be retrieved by identifying the relevant science images through the CFHTLS science observation form and selecting raw calibration images upon retrieval.

  3. Master calibration images

    In Elixir parlance, the calibration process of removing instrumental signatures such as bias levels, dark currents, flat-field variations and fringing from raw science images is known as "detrending" the images. Master calibration images are called master "detrend" images, and processed science images are called "detrended" images. One of the major advantages of Elixir is the ability to use all of the data from a given camera run to produce high-quality master calibration images. Details on the creation of these calibration images can be found on the Elixir Master Detrend page. The following types of master calibration images are produced by the Elixir system: bias, dark, mask, flat-field, fringe, fringe points, and scatter light.

    Dataset names for master detrend images are of the form CRUNID.TYPE.FILTER|EXPTIME.VERSION where CRUNID is the camera run ID, TYPE is the detrend type (e.g, flat), FILTER is the filter used when TYPE=flat,modes,fringe,frpts, scatter, EXPTIME is the exposure time when TYPE = bias, dark and mask, and VERSION is a version number to force the image names to be unique.

    Master detrend images should be available on-line at CADC about three weeks after the end of a MegaPrime run for retrieval through the MegaPrime Elixir master detrend image catalog.

  4. Processed science images

    Processed science images (or "detrended images") are the products of Elixir processing in which master bias, master dark, master flat, master fringe and master scatter light calibrations are applied to the raw science images. Details of these processing steps are available on the Elixir web pages.

    Dataset names for processed images are of the form %dp where %d is the exposure number. Example: 688127p.

    Raw science images are processed at CFHT, and processed images should be available on-line at CADC about three weeks after the end of a MegaPrime run for retrieval through the CFHTLS science image catalog.

  5. Meta-Data

    Data from MegaPrime observations are accompanied by a large amount of meta-data that can be used to document observing conditions, photometric calibrations and processing. Phase I includes four categories of meta-data: (1) nightly photometric solutions from Elixir processing, (2) sky transparency measurements from SkyProbe photometric data, (3) image quality, photometric zeropoints, saturation and limiting magnitudes for processed images, and (4) observing conditions as measured by an array of probes at the telescope,