-- StevenMyers - 2014-03-18

VLASS Technical Working Group (TWG)

This wiki space is for the VLASS TWG to post issues and results.

TWG Document List

Here is a list of documents relevant to the TWG for the test and development program.
  1. The Technical Implementation Plan (TIP) on Authorea [Authorea Link]
  2. A list of VLASS test observations [text list]
  3. A list of proposed VLASS design studies [text file]
  4. The Caltech-NRAO Stripe-82 Survey (CNSS) Paper I [Link]

TWG Technical Issue Discussions

Technical Issue - Data Products

The survey will be defined by the data products. There are a minimal set needed to allow science to be done from the VLASS.

Basic Data Products (BDP): the most basic data products. Processing (resources,algorithms,code) for this will be provided by NRAO and results will be served by the NRAO VLASS server (as well as provided to any mirrors etc.). Some BDP can be produced with work provided by community members where useful and funded, but all BDP must be provided somehow (NRAO will commit to this).

Enhanced Data Products (EDP): extra data products beyond the BDP provided on an opportunity basis by community members (possibly with aid of NRAO in some cases). A good opportunity for additional funding.

Currently defined set::
  • Raw data – it’s whats in the archive by default!
  • Calibrated data – each SB
    • best current output of pipeline (with release notes)
    • BDP (possibly also EDP for special processing)
  • Quick-look images and events – prompt processing
    • Simple intensity images for SB, transient object location
    • BDP (2 weeks) or EDP (48 hours?)
    • EDP for filtered transient alerts
  • Reference images and catalogs – each “epoch”
    • Continuum Intensity and Spectral Index (& curvature?) images [BDP]
    • Polarized IQUV coarse spectral cubes, 128MHz resolution [BDP]
    • Polarized IQUV fine spectral cubes, 10MHz resolution [EDP]
    • Source catalog IQUV, size&shape, spectral index/curv, rotation measure [BDP or EDP?]
  • Refined images and catalogs – each “epoch”
    • As above, plus cross-ids from other wavelengths under EDP
    • Other EDP?
  • Final combined images – over epoch and configuration
    • As above, plus time-series from epochs
    • BDP? Possibly some EDP versions also?

Technical Issue - Imaging Performance

Some references provided by Urvashi & Sanjay:

To-do list:

- set of example datasets (from SWG for possible fields)

- set of imaging script

- people: Sanjay, Urvashi, SMyers, Kunal

Technical Issue - OTF Calibration & Imaging

Issue related to using OTF mosaicking for observations.

To-do list:
  • verify sensitivity for OTF given in JVLA Mosaicking Guide page
  • determine correct overheads for OTF mode long-block observations
  • determine scan rate / data rate limits (assuning 25MB/s max for continuum) for shallow surveys (e.g. 100uJy or higher)
  • verify imaging performance for OTF (S-band B-config) using (1) mfs1 single field + linear mosaic, (2) mfs0 sub-band joint mosaic (3) including POINTING info in above. Includes S/N and accuracy limits and benchmarking.
  • imaging (& calibration) repeatability for multi-epoch observations
  • imaging (& caliibration) performance and limitations using multi-epoch observations to make deeper "static sky" image and sky model
People: SMyers, Kunal, Gregg, Kumar, Sanjay, Urvashi

Technical Issue - Polarization

Polarimetry is a key science goal for VLASS, in particular for RM studies for wide-area surveys and for weak lensing etc. for deeper fields.

To-do list;

- measure polarized primary beam of JVLA in L and S bands

- assess performance of standard polarization calibration and limitations on wide-band mosaicked imaging

- assess performance of wideband widefield polarimetric imaging algorithms for VLASS

- assess performance of Rotation Measure fitting and synthesis for VLASS

People - Preshanth, Sanjay, Cotton

Technical Issue - RFI

It is our experience that S-band (and L-band to a lesser extent) suffer strongly from satellite interference in the geo-synchronous "Clarke" belt, which from the VLA appears at Dec -5.5deg or so. In our S-band Stripe82 work we saw a strong effect when we looked at a calibrator near Dec -3.3deg (and only a small effect at Dec 0). This isn't just interferenece you flag out - it actually seems to compress an entire baseband (1 GHz or half of the 2GHz S-band). It seems to be mitigated by observing at azimuths where the worst offending satellites are far off axis but this means at hour angles away from transit. It probably isn't a show-stopper but I'm guessing the region from -2 < Dec < -10 might be problematic from this regard.

We should do some tests to establish the problem zone and possible mitigation. We should identify soon any such tests needed on the array and arrange to have them done. Some possible tests:
  • OTF fast scans from 0 > Dec > -10 step every 1 deg. Look at Psum,Pdiff etc. to look for gain compression and other effects

Are there other tests we want to do for other RFI (or are the RFI plots from the JVLA Observing Guide sufficient)?

Other Issues?

Archived Content

Topic revision: r19 - 2016-11-18, StevenMyers
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