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Data Reduction

After having enabled the PISCO context (command SET/CONTEXT PISCO), the basic reduction of PISCO data involves merely one command, REDUCE/PISCO, which starts a routine (pisco.prg) solely consisting of other MIDAS commands. So, the whole procedure can be followed when the ECHO facility is enabled (see description for ECHO/ON or ECHO/FULL).
The essential steps are: (1) division of the data by the integration time (stored in descriptor O_TIME), (2) subtraction of the sky and the offset (using a sky measurement, if available, or a dark measurement), (3) calibration (division by calibration file) and (4) Fourier transformation. As is described in Appendix A of the PISCO Operating Manual, the last step, a simple Fourier transform using the MIDAS command FFT/POWER, is the core of the reduction of PISCO data.
The procedure is designed to handle an entire set of data by operating on an input catalog and producing a single output table in which each row holds the results for one data frame in the input catalog. There are no free parameters except for a mode, which can be set to 1, 2, or 3 depending on whether the two sky channels X and Y shall be reduced separately, together, or separately and together, respectively. Normally, the X and Y channel should be treated together.

  
Table: Format of output table produced by REDUCE/PISCO

The program attempts an error estimate from the noise level in the Fourier-transform. The polarisation angles still have an arbitrary zeropoint and need to be transformed to a standard system by means of observations of standard stars. Apart from the comparison with calibration data, the results of REDUCE/PISCO should be final.

The output table is a standard MIDAS table so that all applicable table commands can be used to further process the results. The columns of this table are shown in Table gif.



next up previous contents
Next: IRSPEC REDUCTION Up: PISCO Previous: Data Format



Pascal Ballester
Tue Mar 28 16:52:29 MET DST 1995