OMI Instrument Overview
The OMI instrument is a nadir viewing imaging spectrograph that measures the solar radiation backscattered by the Earth's atmosphere and surface over the entire wavelength range from 270 to 500 nm with a spectral resolution of about 0.5 nm. The 114° viewing angle of the telescope corresponds to a 2600 km wide swath on the surface, which enables measurements with a daily global coverage. The light entering the telescope is depolarised using a scrambler and then split into two channels: the UV channel (wavelength range 270 - 380 nm) and the VIS channel (wavelength range 350 - 500 nm).
In the normal global operation mode, the OMI pixel size is 13 km× 24 km at nadir (along x across track). In the zoom mode the spatial resolution can be reduced to 13 km × 12 km. The small pixel size enables OMI to look in between the clouds, which is very important for retrieving tropospheric information.
The heritage of OMI are the European ESA instruments GOME and SCIAMACHY, which introduced the concept of measuring the complete spectrum in the ultraviolet/visible/near-infrared wavelength range with a high spectral resolution. This enables one to retrieve several trace gases from the same spectral measurement.
The American predecessor of OMI is NASA's TOMS instrument. TOMS uses only 8 wavelength bands, from which the ozone column can be obtained. TOMS has the advantage that it has a fairly small ground-pixel size (50 km × 50 km) in combination with a daily global coverage.
OMI combines the advantages of GOME and SCIAMACHY with the advantages of TOMS, measuring the complete spectrum in the ultraviolet/visible wavelength range with a very high spatial resolution (13 km × 24 km) and daily global coverage. This is possible by using a two-dimensional detector.
OMI was built by Dutch Space and TNO Science & Industry (formerly TNO-TPD) in The Netherlands, in co-operation with Finnish subcontractors VTT and Patria Finavitec. The instrument was financed by the Netherlands Agency for Aerospace Programmes (NIVR) and the Finnish Meteorological Institute (FMI).