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SOLVE HOLOGRAPHY

        CLIC\SOLVE HOLOGRAPHY [NPOINTS npix] [FREE r1 r2 ...]
        [MODES nmodes] [ITER niter gain] [MASK npanels p1 p2 p3 ...]
        [BASELINES b1 b2 b3 ... ]
        [DISTANCE dist] [DIAMETER diam] [DEFOCUS df]
        [TEST testFile] [FRESNEL] [ASTIGMATISM [ANGLE astangle]]
        [/PLOT [AMP amin amax astep] [PHA pmin pmax pstep]
        [ERRORS emin emax estep]  [NUMBER]] [/OFFSET x y z]


    This command computes an antenna surface map from a  set  of  holography
    measurements.  The  set of scans (procedure HOLO) should have first been
    calibrated in phase, amplitude and RF passband relative  to  interspaced
    correlation  scans in the direction of the source.  The map will be com-
    puted from the first band and subband sets chosen with commands SET BAND
    and  SET SUBBAND. SET BAND AVERAGE is recommended for continuum measure-
    ments; only continuum subbands should be used.  For  line  measurements,
    the  continuum width of one of the correlator units should match the ac-
    tual line width for better  sensitivity.   The  antenna  to  be  studied
    should  be  selected  by command SET ANTENNA i.  Data from the baselines
    linking this antenna (scanned) to other (fixed) available  antennas  are
    averaged.


    SOLVING FOR ANTENNA PARAMETERS

    The  amplitude  and  phase maps are obtained by FFT of the observed beam
    map. The maps will be square (npix by npix pixels). The default for npix
    is 64, it should be greater than the number of observed holography scans
    (usually 16 or 32).

    After FFT a gaussian illumination function is fitted in the  amplitudes,
    giving  the  offset  from  the center (in meters) and the edge taper (in
    dB).  If /PLOT is given, the amplitude map will be displayed  (in  deci-
    bels),  from  -15  to  0 dB, with contours in steps of 3db (these may be
    changed using "/PLOT AMP amin, amax and astep").

    A least square fit is used to correct the phases from a remaining  phase
    offset,  pointing  errors,  and focus offsets. The panel rings following
    the keyword FREE are not used for this fit. If /PLOT is given,  the  an-
    tenna  normal surface errors will be shown, in micrometers, from -500 to
    500 mum, with contours in steps of 100 mum (these may be  changed  using
    "/PLOT  ERRORS  emin,  emax  and  estep").  If /PLOT PHASE is given, the
    residual phase map will be plotted instead of surface errors, in radians
    from  -pi to pi, with contours in steps of 0.2 radian. If this map shows
    remaining 2*pi discontinuities, or if focus offsets larger that 1mm  are
    found,  you should try using option /OFFSET to correct the phases for an
    offset (x,y,z in meters) in the focus coordinates, before fitting.  This
    should lead to better rms values.

    The  rms  values for the phase and the normal surface errors (in radians
    and micrometers) are given, both with and without  amplitude  weighting.
    The  contribution  of the illumination amplitude distribution and of the
    observed phase errors to the antenna efficiency are given.

    A gildas image file of the results is kept (e.g. "jj-mmm-yyyy-an1.map"),
    in  which  plane  3  in  the amplitude in dB, plane 4 the raw phases and
    plane 2 the residual phase in radians (plane 1 contains the  fitted  am-
    plitude, i.e.  a Gaussian).


    SOLVING FOR PANEL DISPLACEMENTS

    Finally,  if  "PLOT MODE nmodes" is entered with nmodes larger than 0, a
    listing of panels displacements is computed.  This  uses  the  parameter
    nmodes which is the number of modes used for each panel: 1 is the trans-
    lation mode only (normal to the antenna surface); 3 (the usual  setting)
    adds both tilt modes, radial and tangential, but no panel deformation; 4
    adds a torsion mode and 5 a motion of the panel center relative  to  its
    edges  (there  are  only  5  screws for each panel, thus only 5 possible
    modes).

    The results of this computation is written in  a  file  "panels-an1.dat"
    (or similar name for other antennas). In this file, a line for each pan-
    el is printed. The first two numbers are the panel numbers, followed  by
    up  to  five  screw  settings (three only for the inner ring). All screw
    settings are equal if nmodes was set to  1,  only  one  number  is  then
    printed.

    The  fit is obtained iteratively: the panel orthogonal deformation modes
    are computed from the aperture phase, then the phase change  that  these
    deformations  would  have caused is computed (by doing a FFT to the beam
    map, doing a cut-off at the observed map size, followed by a FFT back to
    the  aperture plane), and subtracted from the aperture phase; second or-
    der panel deformations are computed from these residuals, and so on. The
    number of iterations niter and a gain to this iterative procedure may be
    specified (ITER niter gain); their default values are 5 and  1.0  .  Use
    ITER 0 for no iterative procedure at all. At each step the phase residu-
    al rms and the rms of panel deformations fitted are given  (weighted  by
    the  fitted  amplitude  illumination  and counted perpendicularly to the
    surface).

    Variables containing antenna parameters are available:
      -TAPER_X, TAPER_Y: illumination tapers.
      -OFFSET_X, OFFSET_Y: illumination offsets.
      -RMS_PHA_U, RMS_PHA_W: phase r.m.s (unweigthed or weighted by  illumi-
        nation).
      -ETA,  ETA_230,  ETA_345:  aperture efficiency at observing frequency,
        230 and 345 GHz.
      -ETA_I, ETA_S: illumination and feed taper efficiency.
      -RUZE, RUZE_230, RUZE_345: ruze factor at observing frequency, 230 and
        345 GHZ
      -JYKEL, JYKEL_230, JYKEL_345: antenna efficiency at observing frequen-
        cy, 230 and 345 GHz.
      -HOLO_FOCUS: focus position.
      -HOLO_RMS: surface r.m.s. (unweighted or weighted by illumination).
      -HOLO_RING: rings r.m.s

    SOLVE HOLOGRAPHY options

    SOLVE HOLOGRAPHY NPOINTS npix

        Gives the number of pixels of the amplitude and phase maps.  Default
        is 64.

    SOLVE HOLOGRAPHY MODE nmodes

        Force  CLIC  to compute the panel displacements (see above).  nmodes
        is 1 to 5.

    SOLVE HOLOGRAPHY ITER niter gain

        Select the number of iteration and gain to be  used  for  the  panel
        displacement determination (see above). Does make sense only if used
        in conjonction with the MODES keyword.

    SOLVE HOLOGRAPHY BASELINES b1 b2 b3 ...

        By default, all baselines connecting the antenna to be studied  (se-
        lected  by  SET  ANTENNA)  to  a fixed antenna are used. The keyword
        BASELINES allows to specifically select the baselines to be used.

    SOLVE HOLOGRAPHY MASK npanels p1 p2 p3 ...



    SOLVE HOLOGRAPHY FREE r1 r2 ...

        Indicates the ring NOT to be used for paraboloid fit.

    SOLVE HOLOGRAPHY ASTIGMATISM [ANGLE astAngle] NOFOCUS NOXYFOCUS FOCUS

        Options for fitting. With keyword ANGLE, SOLVE  HOLOGRAPHY  ASTIGMA-
        TISM uses a forced astAngle (in degrees) for astigmatism orientation
        and fits only astigmatism r.m.s.

    SOLVE HOLOGRAPHY POINTING FUDGE CHEAT DEFOCUS df DIAMETER



    SOLVE HOLOGRAPHY TEST testFile

        Use a test beam file instead of real data from the CLIC data file.

    SOLVE HOLOGRAPHY DISTANCE dist

        Gives distance of the source, in meters. Not relevant for astronomi-
        cal sources, of course. Any distance larger than than 1000 km (which
        is the default) forces the FRESNEL approximation.

    SOLVE HOLOGRAPHY FRESNEL


        Use Fresnel approximation (use only the Fourier  transform,  neglect
        the  additional  terms in the complex exponential argument). This is
        the default mode for long distance (e.g. astronomical) sources,  but
        must be indicated if a DISTANCE has been entered.

    SOLVE HOLOGRAPHY /OFFSET x y z



    SOLVE  HOLOGRAPHY /PLOT [AMP amin amax astep] [PHA pmin pmax pstep] [ER-
    RORS emin emax estep] [NUMBER]

        With /PLOT, SOLVE HOLOGRAPHY will plots the results:  two  maps  are
        displayed,  which  by default are the amplitude illumination pattern
        (default plot limits are -15dB to 0dB by step of 3dB) and the anten-
        na  normal  surface  errors  (from -500 to 500 mum, with contours in
        steps of 100 mum). The min., max., and steps  can  be  changed  with
        "/PLOT AMP amin amax astep" and "/PLOT ERRORS emin emax estep". With
        "/PLOT PHASE", the phase residuals are plotted instead of  the  sur-
        face errors. Default are from -pi to +pi by step of 0.2 radians.

        If  NUMBER  is  given  as  a  /PLOT argument, the panels numbers are
        drawn.


Gildas manager 2018-02-24