Soho Cds-nis in-flight intensity calibration using a plasma diagnostic method

The internal intensity calibration of the Coronal Diagnostic Spectrometer (CDS) - Normal Incidence Spectrometer (NIS) is studied using the Arcetri diagnostic method. A large number of spectral lines observed by the CDS-NIS 1 and NIS 2 windows in a solar active region is analysed in order to determine the intensity calibration curve for both channels.The plasma diagnostic method developed in Arcetri allows the measurement of the correction factors to the preliminary CDS-NIS internal intensity calibration curves and the determination of the relative calibration between NIS 1 and NIS 2. A further correction factor of approximately three is found to be necessary for a correct intercalibration of the two wavelength windows. Also the NIS 2 second-order sensitivity is measured. The Arcetri diagnostic method proves to be a powerful tool for intensity calibration studies.