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