A Finnish-French group has proposed an imaging spectrometer-based instrument for the ENVISAT Earth observation satellite ofESA , whichyields a global mapping of the vertical profile of ozone and other related atmospheric gases1. The GOMOS instrument works by measuring the UV-visible spectrum of a stir that is occulting behind the Earth's atmosphere. The prime contractor of GOMOS is Matra Marconi Space France. The focal plane optics are designed and manufactured by Spacebel Instrumentation S.A. and the holographic grating by Jobin-Yvon. VTT Automation, Measurement Technology has participated in the GOMOS studies since 1989 and is presently responsible for the verification tests of the imaging quality and opto-mechanical interfaces of the holographic imaging grating of GOMOS.The UVIS spectrometer of GOMOS consists of a holographic, aberration corrected grating and of a CCD detector. The alignment of the holographic grating needs as an input very accurate knowledge of the mechanical interfaces. VTT Automation has designed, built and tested a characterization system for the holographic grating. This system combines the accurate optical imaging measurements with the absolute knowledge of the geometrical parameters at the accuracy of pm which makes the system unique.The developed system has been used for two breadboard gratings and the qualification model grating2'3'4. The imaging quality results and their analysis together with alignment procedure utilizing of the knowledge of mechanical interfaces will be described.
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