Running the simulator

The simulator has a large number of parameters which may be freely adjusted. The list of parameters is divided between two groups: simulation parameters (usually telescope- and instrument-specific); and observation parameters (properties of the observation in question). These are specified using the SIMPAR and OBSPAR ADAM parameters to sc2sim. For convenience, the parameters are stored in plain text files and are passed in using the ^ scheme mentioned above in Section . Example input files for all major observing modes may be found in the $STARLINK_DIR/share/smurf directory.

The main observation parameters (OBSPAR) of interest are the RA/Dec of the source, wavelength, observing mode (obsmode), observation date and duration of observation (which in the case of SCAN observations, is determined by the size of the area to map). Planets may be specified by name. The RA/Dec must match that in the astronomical image. If the source is not above the horizon, the simulator will exit with an error message. The date must be specified as a UT modified Julian day number. As a point of reference, 20090701T00:00:00 corresponds to MJD 55013.

The main simulation parameters (SIMPAR) are the subarrays to simulate data for, the names of the atmosphere model and astronomical source files and the zenith opacity (at 225 GHz). The zenith opacty is converted to a value at the appropriate wavelength using the empirical relations derived for SCUBA by Archibald et al. (2002). Similar relations for SCUBA-2 will be derived.

Data for all subarrays (at the specified wavelength) may be generated in a single run. The size of the output files is governed by the MAXWRITE parameter for sc2sim which specifies the number of samples to write per file. Multiple observations may be simulated by setting the OVERWRITE parameter to FALSE (the default behaviour is to overwrite existing files).

A word of caution. Since the data output from the simulator mimics the real instrument, it is possible to generate many GB of data which may take many minutes to hours of CPU time. The sc2sim parameter SIMSTATS tells the simulator to estimate the properties of the simulation including the duration of the simulation, quantity of data, memory requirements and CPU time. The results are printed to the screen, allowing the user to modify the simulation parameters if necessary.