[daip] help with UVLSF, please

[Elias Brinks]

Hi Eric,

That makes eminent sense. It does then limit quite seriously
our options for correcting for the aliasing. I'll have to
scratch my head a bit and see if the added uncertainty
in the amplitudes of the channels excluded from the fit
can be tolerated.

Cheers,

Elias


On 11 Dec 2007, at 22:12, Eric Greisen wrote:

> Without even looking at the plots, I think I can answer to some
> extent.  Higher order fits are really not justified by the noise in
> single records of vis data.  In particular, the high order fits are
> not constrained by data in those channels excluded from the fit.  If
> there are too few channels for the S/N and the higher order then
> things will get out of hand in the unconstrained regions of the
> spectrum.  In particular, you will see bad results in scalar averaging
> in which the fact that the phase also got out of hand in those regions
> does not protect you from bad signals.  vector averaging with phases
> wandering wildly will reduce the large amplitudes that appear.
>
> UVLSF with high order will only work if there is really a significant
> continuum signal and you can use e.g at least half the channels in the
> fit.  In particular, the lower numbered channels need to be line
> free.
>
> In other words, this change to UVLSF is not magic although it works
> well in a limited set of circumstances.
>
> Eric Greisen