This application takes
raw SKYDIP data and calculates tau, eta_tel and B by fitting. Sky brightness temperatures are
calculated for different airmasses and then fitted with a model of the sky.
IN = NDF (Read)
The name of the
skydip data file, or, if SCUBA_PREFIX is set, the number of the observation (raw demodulated
data only). The input data file can be the output from
reduce_switch or the raw skydip
data. The file can be located in $DATADIR.
B_ERR = REAL (Write)
Error in the fitted
value of B. Set to bad if the fit has failed.
B_FIT = REAL (Write)
The fitted value of the B
parameter (Filter transmission). Set to bad if the fit has failed.
B_VAL = REAL (Read)
The B parameter (filter transmission). This efficiency factor must be between 0 and 1. A
negative value allows this parameter to be free.
CVAR = LOGICAL (Read)
This parameter
governs whether the points are fitted with a constant variance for all points (true) or the
variance derived from the scatter in the individual integrations (false). The value used for the
fixed variance is the mean of all the calculated variances.
ETA_TEL = REAL (Read)
The
telescope efficiency. If available the current telescope value is used as the default. Values
must be between 0 and 1.0. A negative value allows this parameter to be free. For data
taken before 26 April 2000, the default values supplied for 850 and 450 are provided by the
routine rather than being read from the FITS header.
ETA_TEL_ERR = REAL (Write)
Error in the fitted value of ETA_TEL. Set to bad if the fit has failed.
ETA_TEL_FIT =
REAL (Write)
The fitted value of ETA_TEL. Set to bad if the fit has failed.
GOODFIT =
LOGICAL (Write)
Flag to indicate whether the fit was good (TRUE) or bad (FALSE).
MODEL_OUT = CHAR (Write)
The name of the output file that contains the fitted sky
temperatures.
MSG_FILTER = CHAR (Read)
Message filter level. Allowed values are
QUIET, NORM and VERB. Default is NORM. There are no verbose messages.
OUT =
CHAR (Write)
The name of the output file that contains the measured sky temperatures.
RESIDUAL = REAL (Write)
Absolute difference between the model and the data (in Kelvin).
i.e. ∑abs(Data−Model)
SIGMA = REAL (Write)
Standard deviation of the residuals of the fit (Kelvin).
SUB_INSTRUMENT
= CHAR (Read)
The name of the sub-instrument whose data are to be selected from the input file and
fitted. Permitted values are SHORT, LONG, P1100, P1350 and P2000
TAUZ_ERR = REAL (Write)
Error in the fitted value of TAUZ. Set to bad if the fit has failed.
TAUZ_FIT = REAL (Write)
The
fitted sky opacity for the selected sub instrument.
T_COLD = REAL (Read)
Temperature of the cold
load. The default value is taken from the input file. (This parameter is not required for data
that has been processed by
reduce_switch.)
T_HOT = REAL (Read)
Temperature of the
hot load. The default value is taken from the input file. (This parameter is not required
for data that has been processed by
reduce_switch.)
WAVELENGTH = REAL (Write)
The wavelength of the selected sub instrument.
XISQ = REAL (Write)
The reduced
χ2
of the fit. The nature of the error determination forces the reduced
χ2 to be approximately
1. The SIGMA parameter provides a better guide to the goodness of fit.
If the input file is not found in the
current directory, the directory specified by the DATADIR environment variable is searched. This
means that the raw data does not have to be in the working directory. In addition
IN accepts a number.
This number is converted to a demodulated data filename by prepending it with information specified
in the SCUBA_PREFIX environment variable. This filename expansion only works for demodulated
data (ie data containing ’
_dem_’). The ’
_dem_’ is assumed and should not be present in
SCUBA_PREFIX.
If the CVAR parameter is true the reduced χ2
value can not be used to compare the goodness of fit between datasets.
Both RASTER and DISCRETE skydips are supported.
See Appendix I for more information on skydips.