CALCSKY - Calculate sky contribution from median image

Description:

This routine calculates the sky contribution by attempting to remove the source from the input data stream. The source signal can either be calculated by this routine or by reading in a model of the source from a file.

When calculating the source structure internally a similar method to that used by DESPIKE is employed. The input data are placed into bins of size one quarter beamwidth. The median of each bin is calculated and this is treated as the source model (cf. REBIN_METHOD=MEDIAN in rebin).

Once the source model is available, it is removed from all of the input data. The source-removed data are then analysed with the sky emission derived from the mean of the signal across the array for all the sample times.

Since the sky signal is expected to vary on timescales of the order of one second, an option is included for smoothing the sky signal. This is especially useful for scan map data where samples are taken at 7.8$\sim$Hz.

Usage:

calcsky ref

Parameters:

BOXSZ = INTEGER (Given)

Size of smoothing box in seconds. This is used to smooth the time series. Default is 2.0 seconds.

IN = CHAR (Read)

The name of the input file to be processed. This parameter is requested repeatedly until a NULL value (!) is supplied. LOOP must be TRUE. IN can include a SCUBA section. Like the REF parameter this parameter accepts a text file.

LOOP = LOGICAL (Read)

Task will ask for multiple input files if true. Only REF is read if noloop.

MODEL = NDF (Read)

NDF containing the model of the source. The astrometry is read from this file. The model must have been generated by SURF since it relies on the presence of certain FITS keywords.

MSG_FILTER = CHAR (Read)

Message filter level. Allowed values are QUIET, NORM and VERB. Default is NORM.

NOSRC = NDF (Write)

File to store source removed data. This can be used to check the source removal. Note that this output file can not be used directly by SURF for further processing since the header is incomplete. No file is written by default.

OUT_COORDS = CHAR (Read)

The coordinate system to be used for the model determination. Available coordinate systems are:

• AZ: Azimuth/elevation offsets

• NA: Nasmyth offsets

• PL: RA/Dec Offsets from moving centre (e.g. Planets)

• RB: RA/Dec (B1950)

• RJ: RA/Dec (J2000)

• RD: RA/Dec (epoch of observation)

• GA: Galactic coordinates (J2000)

For RD current epoch is taken from the first input file.

REF = CHAR (Given)

The name of the first NDF to be processed. The name may also be the name of an ASCII text file containing NDF and parameter values. REF can include a SCUBA section. See rebin for more information on the format of the ASCII input file.

SHIFT_DX = REAL (Read)

The pointing shift (in X) to be applied that would bring the maps in line. This is a shift in the output coordinate frame.

SHIFT_DY = REAL (Read)

The pointing shift (in Y) to be applied that would bring the maps in line. This is a shift in the output coordinate frame.

WEIGHT = REAL (Read)

This parameter does nothing in calcsky. It must be present when using text file input. Any value is allowed.

Examples:

calcsky test_rlb model=! $\backslash$$\backslash$

Calculate sky for test_rlb.sdf. Only read in one file and don't use an external source model.

calcsky list.inp model=m82 noloop$\backslash$$\backslash$

Read in the files specified in list.inp and use m82.sdf as a model of the source.

calcsky file nosrc=nosrc boxsz=10.0 $\backslash$$\backslash$

Calculate sky for file.sdf. Store the source subtracted image in nosrc.sdf. Use a smoothing size of 10 seconds.

Notes:

• The model itself is only an approximation to the data (since the data points can fall anywhere within a given cell) so some source signal will remain after source subtraction.

• If a model is supplied externally (via MODEL parameter) the cell size of the model is used for the source subtraction.

• The sky signal is stored in an NDF extension (.MORE.REDS.SKY). The file must be processed by remsky to actually remove the sky contribution.

Related Applications

SURF: remsky