SURF_GRID_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 timesales 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 Hz.

Invocation:

CALL SURF_GRID_CALCSKY ( TSKNAME, N_FILES, N_PTS, N_POS, N_BOLS, N_BOLS, WAVELENGTH, DIAMETER, IMNDF, N_M_FITS, MODEL_FITS, CHOP_THROW, CHOP_PA, BOX_SIZE, BOL_RA_PTR, BOL_DEC_PTR, DATA_PTR, QUALITY_PTR, SKY_PTR, SKY_ERR, BADBIT, STATUS )

Arguments:

TSKNAME = CHARACTER (Given)

Name of task to be used in output messages

N_FILES = INTEGER (Given)

Number of data sets (ie files)

N_PTS ( N_FILES ) = INTEGER (Given)

Total number of points in each map

N_POS( N_FILES ) = INTEGER (Given)

Number of positions per set (Y positions)

N_BOLS( N_FILES ) = INTEGER (Given)

Number of bolometers per set (X positions)

WAVELENGTH = REAL (Given)

Wavelength of observation in microns

DIAMETER = REAL (Given)

Diameter of telescope in metres

IMNDF = INTEGER (Given)

NDF identifier of the supplied model. If this is equal to NDF__NOID then no external model is used.

N_M_FITS = INTEGER (Given)

Number of FITS keywords in the model

MODEL_FITS = CHAR$*$(80) (Given)

FITS keywords from the model

CHOP_THROW = REAL (Given)

Size of chop throw for the first input image (arcsec)

CHOP_PA = REAL (Given)

Chop position angle of first input image (degrees)

BOX_SIZE ( N_FILES ) = INTEGER (Given)

Size of smoothing box - pixels

BOL_RA_PTR( N_FILES ) = INTEGER (Given)

Array of pointers to position information (X coords) Note that each data set has positions for N_POS $*$ N_BOLS

BOL_RA_PTR( N_FILES ) = INTEGER (Given)

Array of pointers to position information (Y coords)

DATA_PTR( N_FILES ) = INTEGER (Given, modified data)

Pointers to actual data arrays. The arrays are modified and contain the source removed data on exit.

QUALITY_PTR( N_FILES ) = INTEGER (Given)

Pointer to quality arrays

SKY_PTR ( N_FILES ) = INTEGER (Pointer Given, data returned)

Storage space for the sky signal

SKY_ERR ( N_FILES ) = INTEGER (Pointer Given, data returned)

Storage space for the error on sky signal

BADBIT ( N_FILES ) = BYTE (Given)

Bad bit mask for identifying bad pixels from quality

STATUS = INTEGER (Given & Returned)

Global Status

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 and the map centre 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

Copyright

Copyright ©1995,1996,1997,1998,1999 Particle Physics and Astronomy Research Council. All Rights Reserved.