Relative intensity calibration of CDS-GIS detectors on SOHO using a plasma diagnostic technique

The internal intensity calibration of the Coronal Diagnostic Spectrometer (CDS) - Grazing Incidence Spectrometer (GIS) is studied using the Arcetri diagnostic method. A large number of spectral lines observed by the four GIS detectors in solar active and quiet regions is analysed in order to determine the relative intensity calibration curve of the instrument. The plasma diagnostic method developed in Arcetri allows the measurement of the correction factors to the pre-flight CDS - GIS internal intensity calibration curves and of the relative calibration between different detectors. No gross deviations from the pre-flight calibration are found. Also the GIS 3 and GIS 4 second order sensitivites are measured. The problems of fixed patterning, ghosting, anomalous line profiles and widths are also discussed, and a list of lines suitable for further diagnostic studies with GIS is presented