VLASS > VLASS Data > Basic Data Products

Basic Data Products

by Davis Murphy last modified Feb 27, 2020

The VLASS Basic Data Products (BDPs) consist of:

  1. Raw visibility data (available from the NRAO archive)
  2. Calibration products (available from the NRAO archive)
  3. Quick Look continuum images (access here)
  4. Single epoch continuum images (including in-band spectral index information) and course (128 MHz channel width) image cubes in Stokes I, Q, U. (to be made)
  5. Single Epoch component catalogs (to be made)
  6. Cumulative VLASS continuum images, and cubes with both coarse and fine (16 MHz) sampling in frequency (the fine cubes will only cover bright regions of emission) (to be made).
  7. Cumulative VLASS component catalogs (to be made).

VLASS data products are labelled by epoch and/or observing campaign (except for the cumulative products). VLASS observing campaigns are scheduled 16 months apart (every time B-configuration is available) and cover half of the sky each, so two campaigns comprise a single epoch. The naming convention is VLASS<epoch>.1 or .2, depending on which half of the sky is covered. For example, VLASS1.1 corresponds to the first half of the first epoch and VLASS1.2 to the second half of the first epoch. Every effort is made to ensure that the sky coverage in each of the halves of the epochs is consistent, so, for example, VLASS2.2 will observe the same part of the sky as VLASS1.2.

The raw visibility data are available immediately after observation from the NRAO archive by searching for programs VLASS1.1, VLASS1.2 etc, and calibration products are also stored there as soon as they are made. The calibration and Quick Look image products are produced as soon as possible (~2-4 weeks) after observations. The schedule for the Single Epoch image products is yet to be determined.

The VLASS Quick Look images are produced using simplified algorithms that result in some compromises in accuracy, and no self-calibration is applied. In addition, the first epoch of VLASS was affected by problems with the online system. These resulted in ghost images, and the first half of the Epoch 1 data (VLASS1.1) has poor flux density accuracy in the Quick Look images due to problems with reported antenna pointings. These issues are described in detail in VLASS Memo 13.

Single Epoch component lists will list source components identified by the source-finding software (pyBDSF). Combination of source components into physical sources will be performed as part of the effort to create enhanced data products.

Data Volume

Data ProductPer Epoch (TB)Total (TB)
Raw visibilities 170 510
Quick Look 4 12
Single Epoch* 400 1200
Cumulative* - 500
Total 574 2222

* - assumes coarse cubes will be made for the whole sky.