Radiometric Results Obtained to Date with the SOHO Extreme Ultraviolet Monitor (SEM) and a Sounding Rocket Underflight

Authors: H. Gruenwaldt, M. Hilchenbach, E. Marsch, P. Bochsler, and F. Ipavich
Reference: Submitted Solar Wind 9 Paper

The absolute full disk solar flux has been measured in two wavelength bands, one band extending from 0.1 to 77 nm and one centered on the 30.4 nm HeII resonance line with a bandwidth of +/- 4 nm. The flux in these bands has been measured using two nominally identical SOHO type transmission grating spectrometers, one of which is being flown on SOHO and another which was on a sounding rocket launched from the White Sands Flight Facility in New Mexico on June 26, 1996. The primary purpose of the sounding rocket flight was to provide "ground truth" calibration of the SOHO CELIAS/SEM spectrometer. The SOHO CELIAS/SEM spectrometer data provide the photoionization rate of He which is flowing into our solar system from the interstellar medium and, additionally, provide a stable absolute EUV flux monitor for cross calibration of other SOHO EUV instruments. A nearly continuous record of the full disk solar flux has been measured since first light was observed on December 16, 1995. SOHO CELIAS/SEM results obtained since first light until September 30, 1996 will be presented as well as the calibration update based on the June 26, 1996 sounding rocket underflight data.

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Last Update: April 2, 1999, James Weygand