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SOLVE BASELINE
CLIC\SOLVE BASELINE [/OFFSET b1 dx1 dy1 dz1 b2 ...]
[/SEARCH range] [/POLYNOMIAL degree]
This uses a linear method to determine baselines. The baselines to be de-
termined must have been selected by the SET BASELINE command, and the data
plotted; plot axes must have been previously selected by : SET X HOUR_AN-
GLE DECLINATION and SET Y PHASE. With SET ANTENNA in action the antenna
position offsets are directly fitted to the antenna phases, ensuring base-
line closure.
The fitting should work only if the starting values are within half a
wavelength in any direction of the true values. Use option /OFFSET to cor-
rect the phases for an offset (dx1,dy1,dz1) in baseline b1 before fitting.
This is needed if the baseline was wrong by more than half a wavelength.
Offsets are to be given in meters.
The results are given as offsets in meters to be added to the base-
line used for data acquisition (which may be read by SIC\EXAMINE BASE-
LINE). The total fitted baseline is also given in meters, as well as
the rms of the residuals in phase units. Two sets of offsets are giv-
en: the first set (dx, dy, dz) are the offsets with respect to the an-
tenna positions actually used, while the secoond set (DX, DY, DZ) are
with respect to the standard antenna coordinates (the default values in
OBS).
The /SEARCH option enables an automatic search with starting offsets
scanning a 3-d box in dx, dy, dz, by steps of half a wavelength in the
three directions. The argument range is in meters (scanning is from
-range/2 to +range/2, default -0.005 to 0.005). Only the solution with
the minimum rms is kept.
With option /POLYNOMIAL degree, and if SET X TIME is used in addi-
tion of HOUR_ANGLE and DECLINATION, a polynomial function of time is in-
cluded in the phase function being fitted. The degree may range from 0
(the default) to 3. In that case command RESIDUALS will also plot the
residuals as a function of time.
Use command RESIDUALS BASELINE to display the fit residuals (phase should
be constant). Use later command PRINT BASELINE to create a procedure file
(named CLIC-BASELINE.OBS) containing the antenna position offsets. This
procedure file may be executed by the observing program OBS on the control
computer bure01.
If one specify elevation as an additional X variable (e.g. SET X HOUR_AN-
GLE DECLINATION TIME ELEVATION), then an additional parameter is fitted:
the offsets between elevation and azimuth axes (or rather the differences
between antennas). These differing offsets result in a phase effect pro-
portional to the cosine of elevation. In antenna mode, these offsets are
given for each antenna in meters. In baseline mode, only differences are
computed. To further correct for this effect use the command MODIFY AXES.
Gildas manager
2011-09-07