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

The internal intensity calibration of the Coronal Diagnostic Spectrometer ( CDS) - Grazing Incidence Spectrometer (GIS) is studied using the Arcetri di agnostic method. A large number of spectral lines observed by the four GIS detectors in solar active and quiet regions is analysed in order to determi ne the relative intensity calibration curve of the instrument. The plasma diagnostic method developed in Arcetri allows the measurement of the correction factors to the preflight CDS - GIS internal intensity calib ration 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 wid ths are also discussed, and a list of lines suitable for further diagnostic studies with GIS is presented.