Intercalibration of SUMER and CDS on SOHO. I. SUMER detector A and CDS NIS

The results of an intercalibration between the extreme ultraviolet spectrom eters Coronal Diagnostic Spectrometer (CDS) and Solar Ultraviolet Measureme nts of Emitted Radiation (SUMER) onboard the Solar and Heliospheric Observa tory (SOHO) are presented. During the joint observing program Intercal_01, CDS and SUMER were pointed at the same locations in quiet Sun areas and obs erved in the same wavelength bands located around the spectral lines He I 5 84 Angstrom, Mg x 609 Angstrom, and Mg x 624 Angstrom. The data sets analyz ed here consist of raster images recorded by the CDS normal-incidence spect rometer and SUMER detector A and span the time from March 1996 to August 19 96. Effects of the different spatial and spectral resolutions of both instr uments have been investigated and taken into account in the analysis. We fi nd that CDS measures generally a 30% higher intensity than SUMER in the He I 584-Angstrom line, while it measures 9% and 17% higher intensities in Mg x 609 A and Mg x 624 PI, respectively. Both instruments show very good temp oral correlation and stability, indicating that solar variations dominate o ver changes in instrumental sensitivity. Our analysis also provides in-flig ht estimates of the CDS spatial point-spread functions. (C) 1999 Optical So ciety of America OCIS codes: 120.5630, 120.6200, 300.6540.