[daip] Re: CVEL accuracy ?

[Nissim Kanekar]

Hi Eric,

This is very useful information indeed, in fact, exactly what I needed. 
Thanks a ton ! I can't see us or anybody else coming anywhere near 4 m/s
accuracy for a long time to come; should have known that AIPS would be 
excellent in this as in most other things.

Thanks again.

Cheers,
Nissim




On Tue, 24 May 2005, Eric Greisen wrote:

> I really know very little about this - the crucial subroutine is
> $APLNOT/DOPLR and its precursor comments say
> 
> 
> C  This version of dop takes into account components of the observer's
> C  motion due to the rotation of the earth, the revolution of the
> C  earth-moon barycenter about the sun, and the motion of the earth's
> C  centre about the earth-moon barycenter.  The perturbations of the
> C  earth's orbit due to planets are neglected.  The absolute precision
> C  of this version of dop is about 0.004 km/sec, but since the dominant
> C  error term is slowly varying the relative error will be considerably
> C  less for times up to a week or so.
> C
> C  The routine omits the planetary perturbations on the earth's orbit.
> C  They amount to about 0.003 km/sec and are thought to be the largest
> C  contribution to the error in the velocity.
> 
> The AIPS routines do not use the elaborate code of calc that takes
> into account earth tides and GR and lots of other things.
> 
> As to documentation - what you see is what you get with aips.  It is
> amazing to me that the astrometry in aips is as good as it is given
> that no astrometrist has been willing to work with the group very
> much.
> 
> Eric Greisen
>