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