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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]
[/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 mea-
surements. The set of scans (procedure HOLO) should have first been cali-
brated in phase, amplitude and RF passband relative to interspaced corre-
lation scans in the direction of the source. The map will be computed
from the first band and subband sets chosen with commands SET BAND and SET
SUBBAND. SET BAND AVERAGE is recommended for continuum measurements; only
continuum subbands should be used. For line measurements, the continuum
width of one of the correlator units should match the actual 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 decibels), 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 antenna
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 ER-
RORS 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 me-
ters) 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 ob-
served 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 amplitude,
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 transla-
tion 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 panel 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 de-
formations 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 order pan-
el deformations are computed from these residuals, and so on. The number
of iterations niter and a gain to this iterative procedure may be speci-
fied (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 residual rms and
the rms of panel deformations fitted are given (weighted by the fitted am-
plitude 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 illumina-
tion).
-ETA, ETA_230, ETA_345: aperture efficiency at observing frequency, 230
and 345 GHz.
-JYKEL, JYKEL_230, JYKEL_345: antenna efficiency at observing frequency,
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 dis-
placement 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 BASE-
LINES 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 NOFOCUS NOXYFOCUS FOCUS
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 astronomical
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 de-
fault 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] [ERRORS
emin emax estep] [NUMBER]
With /PLOT, SOLVE HOLOGRAPHY will plots the results: two maps are dis-
played, which by default are the amplitude illumination pattern (de-
fault plot limits are -15dB to 0dB by step of 3dB) and the antenna
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 surface 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
2011-04-01