Pointing correction

S. Bhatnagar (NRAO)

NAWG, 13 April, 2005

The transform is more complicated (not a FT operator)

General approach:

Major cycle involves: and

Use FT[Xij] to predict the model data (AIM)

Compute VR at high accuracy.

Use an approximation for AT: BT(V-AIM)

Image plane corrections

Primary Beam Effects

FT[Xij] as a function of direction is measured a priori

Primary beam effects

Polarized primary beam: Beam squint

For full beam polarimetry (EVLA)

Pointing offset calibration

For mosaicking (EVLA, ALMA)

Example

Residual image before and after pointing correction.

IV=PB(IRR-ILL)

Peak ~4%

IV=PBRIRR-PBLILL

Peak ~0.2%

Minimize:

to compute A

Pointing solver

Sanjay Bhatnagar

2005-04-13T09:36:30

Sanjay Bhatnagar