The SAMPLER table describes the correlation functions. The order of the rows of the SAMPLER table define the order of the correlations in the DATA column SAMPLER axis in the DATA binary table extension (see below). An example header, plus ASCII listing of typical table data, is given below:
SAMPLER Binary Tables Extension: Header ------------------------------------------------------------------------------- XTENSION= 'BINTABLE' / binary table extension BITPIX = 8 / 8-bit bytes NAXIS = 2 / 2-dimensional binary table NAXIS1 = 118 / width of table in bytes NAXIS2 = 2 / number of rows in table PCOUNT = 0 / size of special data area GCOUNT = 1 / one data group (required keyword) TFIELDS = 4 / number of fields in each row TTYPE1 = 'BANK_A' / label for field 1 TFORM1 = '1A ' / data format of field: 2-byte INTEGER TUNIT1 = 'INDEX ' / physical unit of field TTYPE2 = 'PORT_A' / label for field 2 TFORM2 = '1I ' / data format of field: 2-byte INTEGER TUNIT2 = 'INDEX ' / physical unit of field TTYPE3 = 'BANK_B' / label for field 3 TFORM3 = '1A ' / data format of field: 2-byte INTEGER TUNIT3 = 'INDEX ' / physical unit of field TTYPE4 = 'PORT_B' / label for field 4 TFORM4 = '1I ' / data format of field: 2-byte INTEGER TUNIT4 = 'INDEX ' / physical unit of field POLARIZE= 'AUTO' / 'CROSS' implies poln measurement, else 'AUTO' NUMSAMP = 2 / Number of Samplers Used SAMPUSED= '0 4 ' / Samplers used EXTNAME = 'SAMPLER ' / name of this binary table extension END ------------------------------------------------------------------------------- SAMPLER Binary Tables Extension: Data (complete) ------------------------------------------------------------------------------- ROW BANK_A PORT_A BANK_B PORT_B 1 A 9 A 9 2 A 13 A 13 -------------------------------------------------------------------------------
Each row of the SAMPLER table describes one correlation function produced by the spectrometer. The total number of rows therefore defines the size of the second dimension (TDESC2 = 'SAMPLER') of the third column (TTYPE3 = 'DATA') of the DATA table described in Section 7, and the row number provides the index into this dimension.
Each row contains the value of two ports (which are connected directly to either a fast or slow sampler), PORTA and PORTB (range 1 to 40). For auto correlation, PORTA and PORTB have the same sampler number. For cross correlation, the samplers will have different values. For example in the case of measurement of polarization, two samplers will be used in 4 rows of this table, and the entries will be e.g. XX, XY, YX, YY where X and Y are the two samplers used. For convenience, the POLARIZE keyword specifies whether the scan was intended to be a polarization measurement, in which case FITS file contains cross-correlation data, otherwise it will only contain auto-correlation data.
The definitions of the SAMPLER table-specific keywords are as follows: