Solar Physics Division Meeting 2000, June 19-22
Session 2. Corona, Solar Wind, Flares, CMEs, Solar-stellar, Instrumentation, Other
Display, Chair: J. Krall, Monday-Thursday, June 19, 2000, 8:00am-6:00pm, Forum Ballroom

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[2.15] Re-Calibration of SOHO by SERTS-99

R.J. Thomas, J.M. Davila, W.T. Thompson (NASA/GSFC), B.J. Kent (RAL), J. Hollandt (PTB)

GSFC's Solar EUV Research Telescope and Spectrograph (SERTS) is a rocket instrument that obtains imaged high-resolution spectra of individual solar features to study the Sun's corona and upper transition region. As with SERTS-97, an additional goal of the SERTS-99 flight on 1999 June 24 was to provide radiometric and wavelength calibrations for several experiments on the SOHO satellite mission. For that purpose, a second end-to-end radiometric calibration of SERTS was carried out last fall at RAL in the same facility used to characterize the SOHO/CDS experiment, using the same EUV light source specially re-calibrated by PTB against the synchrotron radiation standard of the BESSY-I electron storage ring. Measurements at a single SERTS aperture position were made to determine the instrument's absolute response within 25% at 12 wavelengths covering its bandpass of 300 -- 365~Å. These were converted into full-aperture values through relative response measurements over a complete range of radial aperture positions. Also, post-flight wavelength calibrations were done at GSFC using well known laboratory lines of He~II and Ne~II. SERTS-99 again carried an EUV solar flux monitor kindly provided by USC; its readings were used to validate our calculations of atmospheric EUV transmission over the rocket's trajectory, and to provide an updated calibration for one of the SOHO/CELIAS channels. During the flight, SERTS-99 and CDS observed the same solar locations, as demonstrated by subsequent data co-registration with simultaneous SOHO/EIT images, allowing the SERTS calibrations to be directly applied to both CDS and EIT. Since it clearly resolves the strong Si~XI and He~II lines blended in EIT's 304~Å\ channel, SERTS gives information on the spectral composition of those images as well. Examples of various cross-calibrations will be compared with results from November 1997, prior to SOHO's temporary loss of pointing control.

This work is supported under NASA RTOP 344-17-38.

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