TROPOMI (Tropospheric Ozone-Monitoring Instrument) is a five-channel UV-VIS-NIR-SWIR non-scanning nadir
viewing imaging spectrometer that combines a wide swath (114°) with high spatial resolution (10 × 10 km2 ). The
instrument heritage consists of GOME on ERS-2, SCIAMACHY on Envisat and, especially, OMI on EOS-Aura.
TROPOMI has even smaller ground pixels than OMI-Aura but still exceeds OMI's signal-to-noise performance. These
improvements optimize the possibility to retrieve tropospheric trace gases. In addition, the SWIR capabilities of
TROPOMI are far better than SCIAMACHY's both in terms of spatial resolution and signal to noise performance.
TROPOMI is part of the TRAQ payload, a mission proposed in response to ESA's EOEP call. The TRAQ mission will
fly in a non-sun synchronous drifting orbit at about 720 km altitude providing nearly global coverage. TROPOMI
measures in the UV-visible wavelength region (270-490 nm), in a near-infrared channel (NIR) in the 710-775 nm range
and has a shortwave infrared channel (SWIR) near 2.3 μm. The wide swath angle, in combination with the drifting orbit,
allows measuring a location up to 5 times a day at 1.5-hour intervals. The spectral resolution is about 0.45 nm for UVVIS-
NIR and 0.25 nm for SWIR. Radiometric calibration will be maintained via solar irradiance measurements using
various diffusers. The instrument will carry on-board calibration sources like LEDs and a white light source. Innovative
aspects include the use of improved detectors in order to improve the radiation hardness and the spatial sampling
capabilities. Column densities of trace gases (NO2, O3, SO2 and HCHO) will be derived using primarily the Differential
Optical Absorption Spectroscopy (DOAS) method. The NIR channel serves to obtain information on clouds and the
aerosol height distribution that is needed for tropospheric retrievals. A trade-off study will be conducted whether the
SWIR channel, included to determine column densities of CO and CH4, will be incorporated in TROPOMI or in the
Fourier Transform Spectrometer SIFTI on TRAQ.
The TROPI instrument is similar to the complete TROPOMI instrument (UV-VIS-NIR-SWIR) and is proposed for the
CAMEO initiative, as described for the U.S. NRC Decadal Study on Earth Science and Applications from Space.
CAMEO also uses a non-synchronous drifting orbit, but at a higher altitude (around 1500 km). The TROPI instrument
design is a modification of the TROPOMI design to achieve identical coverage and ground pixel sizes from a higher
altitude. In this paper capabilities of TROPOMI and TROPI are discussed with emphasis on the UV-VIS-NIR channels
as the TROPOMI SWIR channel is described in a separate contribution .