[daip] Re: specifying a reference frequency in a FITS files for AIPS

[Melissa Soriano]

Eric Greisen,

Thank you for your help.  I made several changes in response to your 
feedback and suggestions.

1.  I changed all of the TFORMn keywords to explicitly specify the repeat 
count, even when it is 1.  This fixed my problem with the invalid reference 
frequency.  My reference frequency is now read correctly by FITLD.

2.  I changed my reference date from 2006-01-01 to 2006-02-10, since this 
is the date of the observation.  I left DATE and TIME in the UV_DATA table 
specified as 32-but float because the "FITS Interferometry Data Interchange 
Format" document lists these random parameters as type 1D.

At 03:13 PM 3/6/2006, Eric Greisen wrote:
>I have looked at the rest of the data and have some doubts of its
>correctness.  After scaling by frequency the baselines are of order
>10^11 wavelengths which seems excessive.  The times are 40.8 + days
>and are not in time order.  Note that the times are in days relative
>to the date given but are kept in 32-bit float.  This loses accuracy
>as soon as the day number exceeds 2 or so.  It is generally not a good
>idea to write data with such large day numbers - chose a closer start
>date.

3. The first ten or so records were repeated out of time order.  I fixed 
this by sorting with respect to time.  The AIPS FITLD task now seems to 
load MAS-TEST19.FITS successfully.

The scaling of the baseline U, V, W coordinates may not be correct.  Should 
the units be seconds or light seconds?

Your feedback has been invaluable.  Thanks for your time.  I will continue 
to work on this.  Attached is a copy of MAS-TEST19.FITS.

Regards,

Melissa Soriano

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