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 NACO, use the options to feed other values. strehl accepts jokers on com- mand 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 following algorithm is applied: 1. Generate a PSF for a given telescope configuration and observation wavelength. 2. Compute the PSF flux and the PSF peak. 3. Detect the brightest star (if not provided on the command line). 4. Compute the star peak and the star flux. This step requires a very precise background estimation. A tiny error on the background can have a strong effect on the computed strehl. 5. Strehl = (star_peak/star_flux) / (psf_peak/pasf_flux) 6. Compute the error on the Strehl 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 computation. Using this option, a FITS file named 'psf1.fits' is generated in the current directory, containing the gen- erated ideal PSF (of Strehl ratio equal to 1). Use it to cross-check that the generated PSF fits your computation. -p diameter Primary mirror diameter in meters. Default to 8. This value is actually 8.2 meters, corrected to take into account the central obscuration ratio. -d diameter Secondary mirror diameter in meters. Default to 1.1. -l 'lambda0 dlambda' Do not forget the simple quotes around the 2 values. First value is the central wavelength of observation. Second value is the filter width. Values are given in microns. Defaults to 5 and 0.1. -s pixelscale Pixel Scale in arc seconds. Defaults to 0.05. -P 'x y' x and y are the pixel position of the star used to com- pute the strehl. If not provided, an automatic bright star detection procedure is applied. -r radius radius is the star radius in arcsecond used to compute the star flux. default is 2.0 arcsec. -R 'rad_in rad_out' These radii define a ring around the star. This ring is used to compute the background. If these values are not provided, a different background estimation method will be used. As the background estimation accuracy is an issue in the strehl ration computation, it is far better to use this option. -b bg Used to provide the backgound value. -S size Size in pixels of the square used to compute the PSF flux. Default is 64 pixels. -T tel Used to define defaults for supported telescopes. Supportes ones are "3.60" and "ut4". Default is "ut4". 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 secon- dary mirror, a central wavelength of 5.0 um and filter 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