[daip] Question about the relation between DPFU and Poly in GC table

[Cui Yuzhu]

Dear Eric,

I thought I found the problem yesterday. So I was too excited to share it with you.
Actually I should check the source code as you recommended by myself first.

Thank you very much for your time.
I will check the source code and the amplitude after applying the SN table with AIPS.
I will tell you as soon as I figure it out.

Have a nice weekend.

Best regards,
Yuzhu





> 在 2019年6月22日，03:19，Eric Greisen <egreisen at nrao.edu> 写道：
> 
> On 06/21/2019 09:28 AM, Cui Yuzhu wrote:
>> Dear Eric,
>> Thank you very much for your explanation.
>> Changing the order of DPFU and Poly means: for example, I create two GC tables, GC1 and GC2.
>> in GC1, DPFU=0.01,Poly=1;
>> In GC2, DPFU=1, Poly =0.01.
>> I expect these two GC table will bring same result. But in reality, they are different.
>> To test this, in page 2, I created 19 GC tables in this way.
>> After calibration in AIPS, I output the data and load them to DIFMAP to check the gain factor by GSCALE.
>> The offset is the gain factor obtained for each data with different GC table.
>> For GC 1 to GC 10, they are all with fixed poly =1. I changed DPFU. The amplitude is inverse
>> proportion to DPFU (G in the formulae in page 2). That is consistent with the expectation.
>> For GC 11 to GC 19, they are all with fixed DPFU=1. I changed Poly. But the results are same.
>> So I guess when we have only one parameter in Poly which represent the DPFU is constant with the elevation,
>> AIPS will scale the poly to 1 no matter what value it originally is.
>> Is this right?
>> 
> 
> I have looked at the code that I recommended to you.  In it, there is no normalization of the polynomial.  It returns a gain that is the product of the sensitivity (DPFU in your nomenclature) and the polynomial and so should return different numbers for your 19 GC tables
> 
> You say "after calibration in AIPS" - this includes rather more than just APCAL (which is the only task to use the GC table).  To see what changing the GC table does, you should examine the amplitudes in the SN table produced by APCAL.  It might be instructive to examine the amplitudes in the final CL table as well - which will include all of the other calibration tasks.  ACCAL and ACSCL also modify the gain so the latter might compensate for a change in the GC table.
> 
> Going to DIFMAP for some parameter "GSCALE" is confusing to me.  Use SNPLT to look at the SN and CL table gain amplitudes.
> 
> Eric Greisen

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