SWRI/LASP sounding rocket inter-calibration with the EIT instrument on board SOHO

Two successful sounding rocket flights were launched on 15 May 1997 and 2 N ovember 1998 with an objective of providing inter-calibration with several of the instruments on board SOHO and TRACE. We will discuss here the result s of the inter-calibration between the SwRI/LASP rocket imaging instruments and the Extreme-ultraviolet Imaging Telescope (EIT) on SOHO. The Multiple XUV Imager (MXUVI) sounding rocket instrument is a multi-layer mirror teles cope equipped with an internal occulter and light trap to provide full-disk images of Fe IX/X 17.1 nm and off-limb observations of He II 30.4 nm. The SOHO/EIT instrument is also a full-disk multi-layer imager with four channe ls, Fe IX/X 17.1 nm, Fe XII 19.5 nm, Fe XV 28.4 nm and He II 30.4 nm. By co mparison with the EIT observations taken at the same time, we provide new f lat-field determinations for EIT which help quantify the sensitivity degrad ation of the EIT detector, as well as provide a measure of the off-limb str ay-light characteristics of the two instruments. We find that the EIT stray -light function is strongly asymmetric, with greater stray light in the 17. 1 and 19.5 nm quadrants than the 30.4 and 28.4 nm quadrants. Two possible c auses of this asymmetry are the polishing processes of the EIT mirrors and the asymmetric support grid pattern in the foil mesh at the EIT pupil.