I think the problem with creating a new definition of signal to noise is that this is an attempt to make something that corresponds to the quality of the measurement, while the true signal to noise is only a measure of the quality of the signal. This can be used for estimating the time needed for a measurement to obtain the desired statistics, but should not be used as a way to judge the quality of a completed measurement.
As far as taking the sum of the squares, it is my understanding that the signal to noise is intended to be applied to a single mode, so the true signal-to-noise could vary widely for different modes. As I mentioned, it can be a very useful predictor of the time needed for the measurement, but probably shouldn't be used in discussing the quality of the measurement. If you are interested in a peak other than the one for the highest mode, you should use that peak when estimating the time needed for a measurement. Another link is http://en.wikipedia.org/wiki/Signal-to-noise_ratio Tom Worlton -----Original Message----- From: Leonid Solovyov [mailto:[EMAIL PROTECTED] Sent: Tuesday, February 19, 2008 3:51 AM To: rietveld_l@ill.fr Subject: RE: advice on new powder diffractometer > It seems to me that if there is no internationally accepted definition > of signal to noise ratio in powder diffraction, then let me suggest >that this forum might be a way to define it once and for all. How >about this? > SNR = (P-B)/SQRT(B). > > Of course this would only give a value for a single peak. I suppose > one could also define a global SNR as a sum over all Global SNR = sum > over peaks (P-B)/SQRT(B). > > Does this make sense? > Mike A more overall value would be a normalized sum of the ratios (Ip-Ib)/sqrt(Ib), where Ip and Ib are the profile intensities of the pattern and the background for each datapoint. Leonid ________________________________________________________________________ ____________ Looking for last minute shopping deals? Find them fast with Yahoo! Search. http://tools.search.yahoo.com/newsearch/category.php?category=shopping
