[daip] SNR calculations in FRING

[Leonia Kogan]

You wrote:

>And the noise is the RMS thermal
>noise determined by the data integration time and the maximum
>recording bandwidth. Then SNR is simply a ratio between both.

SNR may be inversely proportional to the square root of the
product of both but not their ratio.

>The baseline stacking (if applied) could reduce the noise to
>eventually increase the SNR measured for each datum. Is this
>exactly what written in the FRING source code?

Not exactly. The fringe rate esimation is carried out at the FRING
having amplitude clipped before the estimation. This makes the
estimation of the errors more complicate. 
Desai Ketan spent a time to make a beter math analysis of the problem and 
implemented his ideas at the FRING's code.

There are relevant memos at the AIPS and VLBA serios about that and about stacking

Leonia
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Subject: [daip] SNR calculations in FRING
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Date: Thu, 1 Aug 2002 14:53:04 +0900
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Hi,

I have a dumb question about the SNR calculation in FRING
at the first FFT fringe detection stage.

The presumed signal amplitude can be measured at the peak
in the delay-rate spectrum. And the noise is the RMS thermal
noise determined by the data integration time and the maximum
recording bandwidth. Then SNR is simply a ratio between both.
The baseline stacking (if applied) could reduce the noise to
eventually increase the SNR measured for each datum. Is this
exactly what written in the FRING source code? The weights
may also need to be included in a not so straightforward way.

There are essentially two different FRING modes in FRING. One
with aparm(5)=0 will do fringe fitting on each IF independently,
the other with aparm(5)>1 will solve for multi-band solutions.
No matter what choice we use, the noise estimation will always
assume a maximum bandwidth, i.e., the whole observing band.
Is this right?

Best regards from


---------------------------------------------------
Zhi-Qiang Shen
The Institute of Space and Astronautical Science
3-1-1 Yoshinodai, Sagamihara
Kanagawa 229-8510, JAPAN
Tel: +81-42-759-8346	Fax: +81-42-759-8485
E-mail: zshen at vsop.isas.ac.jp
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