SCUBA

The SCUBA extension contains information on the instrument and the structure of the data array. It has the following format (output of hdstrace):

SCUBA          <SCUBA_ST>      {structure}
   BOL_CALB(16,9)  <_REAL>        1.286,0.9311,0.9499,1.002,0.9585,
                                  ... 1.054,1.065,1.045,1,1,1,1,1,1,0
   BOL_DU3(16,9)  <_REAL>         57.08,45.9,36.15,24.64,14.55,3.62,
                                  ... -15.78,9.047,-54.65,0,0,0,0,0,0
   BOL_DU4(16,9)  <_REAL>         -28.14,-35.91,-41.46,-49.62,
                                  ... 63.89,77.76,71.16,0,0,0,0,0,0
   BOL_QUAL(16,9)  <_INTEGER>     0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
                                  ... 0,0,0,0,0,0,0,0,0,0,1,1,0,0,0,1,1
   BOL_TYPE(16,9)  <_CHAR*20>     'SHORT','SHORT','SHORT','SHORT',
                                  ... 'P...','P1350_DC','P1100_DC','BAD'
   BOL_ADC(128)   <_INTEGER>      1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,
                                  ... 8,8,8,8,8,8,8,8,9,9,9,9,9,9,9,9,9
   BOL_CHAN(128)  <_INTEGER>      1,2,3,4,5,6,7,8,9,10,11,12,13,14,
                                  ... 12,13,14,15,16,1,2,3,4,5,6,7,8,9
   FLAT_ADC       <_INTEGER>      0
   FLAT_CHN       <_INTEGER>      0
   FLAT_IND       <_INTEGER>      0
   PHOT_BB(3,2)   <_INTEGER>      0,112,0,0,46,0
   DEM_PNTR(2,4,3,1)  <_INTEGER>   1,17,49,33,65,81,113,97,129,145,
                                   ... 257,273,305,289,321,337,369,353
   ISTART         <_INTEGER>      0
   NPIX           <_INTEGER>      0
   POINTER        <_INTEGER>      0

The first 5 entries are simply the flatfield information (see Appendix for an example flatfield file). The shape of the arrays (in this case $16\times9$) corresponds to the number of channels on each A/D card and the number of A/D cards. These dimensions must match the values of the constants SCUBA__NUM_ADC and SCUBA__NUM_CHAN (Appendix ).

The full description of these entries follows:

BOL_CALB

These are the actual flatfield values and contain the response of each pixel relative to a reference pixel (usually the centre pixel on each array, H7 and C14). This correction is applied to the data using the flatfield task (specifically the sculib_flatfield_data routine):

$$V_\mathrm{flatfielded}(B) = V_\mathrm{original}(B) \times \mathrm{BOL\_CALB}(B)$$ (1)

where $B$ is the selected bolometer.

BOL_DU3

These are the X coordinates of every bolometer. For SCUBA, these are arcsec X (U3) offsets (i.e. $\mathrm{d}U3$) from the left-hand Nasmyth centre.

BOL_DU4

These are the Y coordinate of every bolometer. For SCUBA, these are arcsec Y (U4) offsets (i.e. $\mathrm{d}U4$) from the left-hand Nasmyth centre.

BOL_QUAL

This is an array of quality flags. A 0 indicates that the bolometer is `good', a 1 indicates that the bolometer is `bad'. This array is used during flatfielding (sculib_flatfield_data)to set bit 1 in the NDF quality array.

BOL_TYPE

This array contains a textual description of the sub-instrument to which each bolometer belongs. This information is used by the extinction task to select the bolometers from the specified sub-instrument.

BOL_ADC

This array contains the A/D card numbers corresponding to each of the bolometers that were used for the observation. The order and size should match the size of the second dimension of the main data array for raw SCUBA data and the first dimension for data that has been processed by reduce_switch. The extinction task modifies this array to reflect the sub-instrument selection.

BOL_CHAN

This array contains the A/D channel numbers corresponding to each of the bolometers that were used for the observation. The order and size should match the size of the second dimension of the main data array for raw SCUBA data and the first dimension for data that has been processed by reduce_switch. The extinction task modifies this array to reflect the sub-instrument selection.

FLAT_ADC

Not used by SURF.

FLAT_CHN

Not used by SURF.

FLAT_IND

Not used by SURF.

PHOT_BB

This is only used for PHOTOM (and POLPHOT) observations. The first dimension corresponds to the number of beam positions (3 for 2 position chopping with nodding) and the second dimension corresponds to the number of sub-instruments used for the observation. The array contains the bolometer number (using the same indexing scheme as for the BOL_CHAN and BOL_ADC arrays) that is on source for each of the beam positions. For standard single bolometer photometry only the middle beam is on source and in the example shown only H7 and C14 are used for the photometry. The scuphot task uses this array to decide which bolometers to extract from the full dataset. The extinction task modifies this array to reflect the sub-instrument selection.

This information is also available in string form in the PHOT_BBF FITS keyword. For non-PHOTOM based observations this structure is 0.

DEM_PNTR

This array is used to convert from measurement, integration, exposure and switch number to sample number (i.e. the final dimension in the data array). The routines SCULIB_FIND_SWITCH and SCULIB_FIND_INT are provided to simplify this (they also return the position of the end of the switch or integration). It has dimensions of N_SWITCHES, N_EXPOSURES, N_INTEGRATIONS, and N_MEASUREMENTS.

ISTART

Not used by SURF.

NPIX

Not used by SURF.

POINTER

Not used by SURF.