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ccdspec - print spectrum at a grid point in an image cube


ccdspec [parameter=value]


ccdspec prints the spectrum (see also snapprint(1NEMO) for more flexible options) to stdout, with a commented line that adds some statistics on the standard deviation of the series and that of the differentials. It also computes sigma_diff/sigma/sqrt(2) , which should be 1 if the spectrum is normal and uncorrelated noise. In general smoothing and/or a signal will lower this value.


The following parameters are recognized in any order if the keyword is also given:
Input filename. No default.
Pixel in X to print (0=1st pixel). By default it uses the center of the map.
Pixel in Y to print.
Pixel range in Z to select. By default all pixels are selected.
Output scaling factors for the spectral axis (fac1) and cube value (fac2). Note the mean/sigma output will also be scaled by fac2. [Default: 1,1]


Here is an example creating a spectrum with uncorrelated noise. The stats mentioned in the commented last line ar the pixel position and length of spectral axis, and mean/sigma for the signal, and mean/sigma he differential spectrum. The last number is the ratio of the two sigma and sqrt(2) , which for normal gaussian noise should be 1.
% ccdgen - noise 0,1 size=1,1,8000 seed=123 |  ccdspec - | tail -3
7998 -1.06975
7999 0.944338
# 0 0 8000 mean/sig  0.00102038 1.00182    9.94952e-05 1.41469   0.998513
although tabhist(1NEMO) with median=f gives the same stats
% ccdgen - noise 0,1 size=1,1,8000 seed=123 |  ccdspec - | tabhist - 2  median=f
Mean and dispersion  : 0.00102037 1.00182 0.0112014
Diff mean and disp   : 9.94952e-05 1.41469 0.998513
and if an extra hanning smoothing is done, the correlation is less than one (sqrt(1/3)):
% ccdgen - noise 0,1 size=1,1,8000 seed=123 | ccdsmooth - - dir=z | ccdspec
- | tail -3
7998 -0.151399
7999 0.204732
# 0 0 8000 mean/sig  0.000986234 0.616406    4.92386e-05 0.49548   0.568387

See Also

ccdgen(1NEMO) , ccdprint(1NEMO) , tabhist(1NEMO) , tabtrend(1NEMO)




Peter Teuben


11-Feb-2021    V0.3 Created Q&D    PJT
21-dec-2022    V0.6 Added ascii header    PJT

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