Allowed operations are adding, subtracting, multiplying, dividing, replacing, and polarization calibration or simulation. The model is specified in the image domain, so that its Fourier transform is first computed before application to the visibilities. The model may be either an image (e.g., a CLEAN component image) or a point source.
An example is as follows. UVMODEL could be used to remove CLEAN components from a visibility data file. The residual data base could then be examined for anomalous points, which could in turn be clipped. UVMODEL could then be reapplied to add the CLEAN components back into the visibility data base for re-imaging.
add Form: out = vis + model subtract Form: out = vis - model multiply Form: out = vis * model divide Form: out = vis / model replace Form: out = model flag Form: out = vis, but flag data where the difference between vis and model is greater than "sigma" sigmas. polcal Correct polarization leakage using a total intensity model. out = vis - model * (polcor(q,i)+conjg(polcor(p,j))) where p,q are the polarization and i,j the antennas. poleak Simulate polarization leakage using a total intensity model. out = model * (polcor(q,i)+conjg(polcor(p,j))) where p,q are the polarization and i,j the antennas. unflag Unflag any flagged data in the output. autoscale Adjust the scale of the model to minimise the difference between the model and the visibility. apriori Use flux from flux table or data file planet info. imhead Much ``header'' information in the uv file is ignored -- the model information is used instead. In particular, the observing center of the uv file is taken to be the reference pixel of the model. By default, if the reference pixel and the uv data observing center are different, a phase shift is applied to the model visibilities to align them. The ``imhead'' option prevents this shifting. selradec This causes UVMODEL to select only those visibilities whose observing center is within plus or minus three pixels of the model reference pixel. This is needed if there are multiple pointings or multiple sources in the input uv file. By default no observing center selection is performed. polarized The source is polarized. By default the source is assumed to be unpolarized. For a polarized source, UVMODEL cannot perform polarization conversion. That is, if the model is of a particular polarization, then the visibility file should contain that sort of polarization. For example, if the model is Stokes-Q, then the visibility file should contain Stokes-Q. mfs This is used if there is a single plane in the input model, which is assumed to represent the data at all frequencies. This should also be used if the model has been derived using MFCLEAN. zero Use the value zero for the model if it cannot be calculated. This can be used to avoid flagging the data in the outer parts of the u-v-plane when subtracting a low resolution model.The operations add, subtract, multiply, divide, replace and flag are mutually exclusive. The operations flag and unflag are also mutually exclusive.
The unflag option should be used with caution. Data in the output may still be flagged, if it was not possible to calculate the model.
type,nchan,start,width,stepGenerally if there is an input model, this defaults to the linetype parameters used to construct the map. For a point source or planet model, the default is all channels. If you wish to override these defaults, or if the info is not present in the header, this parameter can be useful.
systemp = 2.*(Trx + Tsky*(1-exp(-tau/sinel)))*exp(tau/sinel)where systemp, Trx and Tsky are in Kelvin. Typical values for Hat Ck Trx, Tsky, and tau are 75,290,0.15. (OBSTAU gives values for tau). systemp is used to generate random Gaussian noise to add to each data point. Default is 0,0,0 (i.e. no additive noise).