Name
strehl - Strehl ratio computation
Synopsis
strehl [options] <cubes...>
Description
strehl computes the Strehl ratio for every plane in every
cube given on command line. See ALGORITHM to know how it
is computed. strehl needs to know some parameters about
the mirror and observation wavelength to generate the
ideal PSF. Defaults for these parameters are taken for
Adonis, use the options to feed other values. strehl
accepts jokers on command line :
> strehl *.fits
ATTENTION! The input image must be square (same size in x
and y), and this size shall be a power of 2! This to allow
a correct PSF generation.
Algorithm
For each image in each cube (candidate image), the follow-
ing algorithm is applied:
1. Generate a PSF for a given telescope configuration and
observation wavelength.
2. Normalize the PSF and candidate image to unity flux.
3. Do Strehl = MAX(candidate) / MAX(PSF)
Where MAX is the maximum pixel in the image.
Attention: the theoretical PSF is generated only once per
call! When giving several cubes on command-line, it is up
to the user to check that the same parameters are valid
for all files (check the wavelength).
Options
-g An ideal PSF is generated for Strehl ratio computa-
tion. Using this option, a FITS file named
'strehl1.fits' is generated in the current direc-
tory, containing the generated ideal PSF (of Strehl
ratio equal to 1). Use it to cross-check that the
generated PSF fits your computation.
-p PrimaryDiameter
Primary mirror diameter in meters. Defaults to
3.47. This value is actually 3.60 meters, corrected
to take into account the central obscuration ratio.
-d SecondaryDiameter
Secondary mirror diameter in meters. Defaults to
1.66. This value is actually 1.57 meters, corrected
to take into account the central obscuration ratio.
-l 'lambda0 dlambda'
Do not forget the simple quotes around the 2 val-
ues. First value is the central wavelength of
observation. Second value is the filter width. Val-
ues are given in microns (1e-6 m).
Defaults to 2.2 and 0.3.
-s pixelscale
Pixel Scale in arc seconds. Defaults to 0.05.
Example
To compute the strehl ratio over 10 cubes named S001.fits
to S010.fits, on an 8 meter telescope with a 1.5 meter
secondary mirror, a central wavelength of 5.0 um and fil-
ter width of 0.1 um, a pixel scale of 0.05, use:
strehl -p 8 -d 1.5 -l '5 0.1' -s 0.05 S*.fits
Files
Files shall all comply with FITS format
See Also
stcube