
Delivered-To: oxborrow@dsri.dk
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Date: Mon, 6 May 2002 16:04:47 +0300 (EEST)
From: Sami Maisala <smaisala@astro.helsinki.fi>
To: Niels Joergen Westergaard <njw@dsri.dk>
Cc: Peter Kretschmar <Peter.Kretschmar@obs.unige.ch>, Stefan Larsson <stefan@astro.su.se>, Carol Anne Oxborrow <oxborrow@dsri.dk>
Subject: Re: ADD and bkg
MIME-Version: 1.0


Hi Niels Joergen,

Thank you for your comments :-)
here is my response of your questions.

> 
> Page 109:
> 
>    In section 'Function': 'Simulated and observed shadowgram catalogues are
>    indexed group tables where each model is a separate FITS file.'
>    
>    Is it really necessary that they are in individual FITS files? This is
>    in contradiction with the ISDC grouping philosophy.

	You are right. This must be changed. The models are not individual 
        FITS files. They are all included in indexed group table.
 

>    
>    In section 'Instrumental background': 'The results are multiplied with
>    each other ...'
>    
>    Please give some more explanation. It is not clear to me what 'results'
>    precisely refers to and why they should be multiplied.

	I think the expression multiply is wrong. See below.
> 
> I have some difficulties to follow your description of the subgroups.
> Your claim is that there are three important parameters: orbital phase,
> sun aspect angle, and radiation level, that will completely determine the
> spatial and spectral shape of the background.
> The next assumption is that each of these three will give rise to a
> particular shape ( you hint at this in the diagram, page 118, where you
> suggest that the orbital phase will decide the edge effects, the
> sun angle will decide the "skewness" of the background, and the radiation
> level will determine the more complicated shape).
> So instead of working in a 3-dimensional space (which, admittedly, will be
> very complex) you have chosen to work in 3 one-dimensional spaces
> that you combine by this multiplication process.
> 
> Can you agree with these statements? Or have I got ot wrong?
> 

yes I agree. The idea is to work in sub groups (blocks). I use term 
'sub-group' to make difference between different type of models. In each 
sub-group we are using  only one decisive parameter - The others are set 
to the disregard values (-1) 

The first step is to use the sub-group where we are using information of the 
orbital phase. In this case we select the two closest models from 'orbital 
phase sub-group' by selecting the shortest distance between orbital phase 
and the database parameter values. These selected models are interpolated 
to the one 'orbital phase sub-group' model by using information of the 
models  spatial distribution and they are weighted with the coeffecients 
which are propotional of the differences between models distances and the real 
orbital phase.

Second step is to use  'sun angle sub-group' and as above we select the 
two closest models and make interpolation between them.  

third step is 'radiation level sub-group' and the selection method is 
same.


After this 3 steps we have 'results' as three interpolated models from 
the each sub-group and the next step is to combine them to the one normalized 
bkg model. In document I have used expression 
'The results are multiplied which each other and normalized...'
I think this is misleading information. 

In our case we should make  the 
combination by adding these models together and then make a normalization 
and the result is the final combined normalized bkg model. 
     
Do you agree?



How about the diffuse bkg handling? I tried to put shortly together that 
what we discussed in our last meeting. Do you agree that?

I have few missing pieces in this whole picture.
Would you send me your ideas what you had in your mind in that meeting.
There was few things I couldn't quite follow. I have questions like:

What we actually put in our galactical diffuse bkg catalogue?

How to use and calculate the tilt angle?

what was the model selection function?

What is the effect of the roll angle if we are using 
the same diffuse bkg model over the whole detector?

 
 Regards,

Sami


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