Scientific requirements and optical design of the ozone monitoring instrument on EOS-CHEM

The Ozone Monitoring Instrument (OMI) is a Dutch-Finnish contribution to NASA's EOS-Chemistry satellite, which is due to be launched in December 2002. The aim of OMI is to contribute to climate monitoring and atmospheric chemistry research by providing daily global measurements of the total ozone column, ozone profile, NO2 column, other trace gases like SO2 and BrO, aerosols, cloud fraction, cloud top pressure, and surface UV irradiance. The optical design of OMI is based on the heritage of GOME and SCIAMACHY, and is suitable to perform TOMS-and SBUV-type measurements. The electronics of OMI has a heritage from GOMOS. OMI is an imaging spectrometer with a spectral range 270-500 nm, a spectral resolution of 0.45-0.6 nm, and a wide field-of-view (114 degrees). For most wavelengths the groundpixel size is 13 x 24 km(2) in the global mode. There are two channels: UV channel, which is split into two parts to reduce straylight, and a visible channel. Both channels have a two-dimensional CCD as detector. Polarization of the incident light is scrambled. For in-flight calibration, OMI can measure sunlight, and onboard white-light and LED sources.