Structure of demodulated files

Demodulated data files are much more complicated as they have to contain a full description of the state of SCUBA for each observation. Here is an example trace (the map of 3C279 used in the example):

% hdstrace apr8_dem_0059
 
STRUCT  < >
 
   MORE           <EXT>           {structure}
      FIGARO         <FIGARO_EXT>    {structure}
         {structure is empty}
 
      SCUCD          <SCUCD_ST>      {structure}
         JIGL_X(64)     <_REAL>         5.3457,0,-5.3457,-8.033999,
                                        ... 0,-5.3457,-8.033999,-2.6883,2.6883
         JIGL_Y(64)     <_REAL>         12.36,12.36,12.36,10.815,10.815,
                                        ... -9.27,-10.815,-10.815,-10.815
         DEC1           <_REAL>         0
         DEC2           <_REAL>         0
         LST_STRT(2,4,3,1)  <_DOUBLE>   3.23079147492436,3.2322998582771,
                                        ... 3.26511400298336,3.26350802081885
         RA1            <_REAL>         0
         RA2            <_REAL>         0
 
      SCUBA          <SCUBA_ST>      {structure}
         BOL_CALB(16,9)  <_REAL>        0.858,0.9311,0.9499,1.002,0.9585,
                                        ... 1.213,0.928,1.304,1,1,1,1,1,1,0
         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        <_INTEGER>      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(62,2,4,3,1)  <_INTEGER>   20,19,18,18,18,18,18,15,14,13,
                                          ... 14,13,14,16,22,23,31,41,0,0,0,0
         NPIX(62,2,4,3,1)  <_INTEGER>   2,5,12,13,28,29,29,32,33,34,34,35,
                                        ... 37,36,34,32,30,24,23,14,3,0,0,0,0
         POINTER(62,2,4,3,1)  <_INTEGER>   2,4,9,21,34,62,91,120,152,185,
                                           ... 52804,52807,52807,52807,52807
 
      FITS(164)      <_CHAR*80>      'ACCEPT  = 'not used'           / ac...'
                                     ... 'WAVE_5  =                 ...','END'
 
   DATA_ARRAY(5,128,384)  <_REAL>   0.011504,0.000014,0.029308,0.000015,0,
                                    ... 0.006727,0.000003,0.022551,0.000003,0
                                        ... 0,0,0,0,0,0,0,0,0,0,1,1,0,0,0,1,1

End of Trace.

From this we can see that there is a 3 dimensional data array and 4 NDF extensions. Each will be described in turn:

DATA_ARRAY

The data array contains three dimensions. The first dimension is a vector of size 5 and relates to the chop data, the chop error, the calibrator data the calibrator error and the quality respectively. The second dimension is the bolometers and the third is the number of measurements (ie number of jiggle positions $\times$ number of integrations $\times$ 2 (number of nods)). These data can be displayed to examine each component in turn (for example checking whether the OFF position contains a source) by using NDF sections.

FIGARO extension

The FIGARO extension is not used by the SURF package.

SCUCD extension

The SCUCD extension contains information on the position of the telescope for each sample along with the local sidereal time of each sample.

SCUBA extension

The SCUBA extension contains the flatfield information (position of the bolometers, sub-intrument of bolometers, quality of bolometers and A-to-D card). There are also arrays to aid in the location of each jiggle in the data array (DEM_PNTR).

FITS extension

The FITS Extension is described in the next appendix.

In addition a new extension is created by the SURF package itself. This extension (called REDS for historical reasons) contains beam weights for chopping, and pointing corrections. In general this extension is created for PHOTOMetry observations and by the change_pointing task.

A more detailed description of the file format can be found in Starlink System Note 72.