Documentation on conterr

Task: conterr
Purpose: Continuum subtraction error estimate, when using UVLIN.
Categories: uv analysis

        Given an image of the continuum in a spectral line experiment,
        CONTERR estimates the residual continuum artifacts that will
        be present after continuum subtraction using UVLIN. The results
        are intended to be indicative, rather than rigorously accurate.
        The peak value and location of the errors are approximately
        correct, but the actual error pattern will differ significantly
        from that presented here.

        This task essentially just evaluates the expressions given
        in Table 1 of Bob Sault's paper ``An analysis of visibility-based
        continuum subtraction''.
        CONTSEN makes plots of noise amplification factor of tasks such
        as UVLIN, AVMATHS and CONTSUB.

Key: in
        An extimate of the continuum. It should be either a dirty image
        or a deconvolved/restored image. No default.

Key: order
        The order of the polynomial fit in UVLIN. Either 1 or 2 numbers
        can be given. If two numbers are given, then CONTSEN determines
        the error for order(1) to order(2) inclusive. The
        default is to determine the noise sensitivity for first order
        only.

Key: bw
        Total spectral bandwidth, in GHz. Default is 0.008 (i.e.
        8 MHz).

Key: fwhm
        The image resolution, given as the FWHM of the corresponding
        gaussian, in arcsec. This is the same as the FWHM that
        RESTOR would determine. The default is to get the information from
        the input image. Two values can be given, being the FWHM in
        x and y respectively (i.e. the position angle is assumed to
        be along one of these axes). If only one value is given, the
        gaussian is assumed to be circularly symmetric.

        Note that high order fits are very sensitive to this parmeter.

Key: out
        An output image containing the error images. The default is
        no output image.

Key: options
        Extra processing options. Several can be given, separated by
        commas. Minimum match is used. Possible values are:
          shift  Determine an optimum shift of the phase centre to
                 be applied before the error is evaluated. This
                 shift will minimise the error in some sense.