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The Tropospheric Monitoring Instrument, TROPOMI, is a passive UV-VIS-NIR-SWIR spectrograph, which uses sun backscattered radiation to study the Earth's atmosphere and to monitor air quality, on both global and local scale. It follows in the line of SCIAMACHY (2002) and OMI (2004), both of which have been very successful. OMI is still operational. TROPOMI is scheduled for launch in 2015. Compared with its predecessors, TROPOMI will take a major step forward in spatial resolution and sensitivity. The nominal observations are at 7 x 7 km2 at nadir and the signal-tonoises are sufficient for trace gas retrieval even at very low albedos (2 to 5%). This allows observations of air quality at sub-city level. TROPOMI has reached CDR status and production of flight model units has started. Flight detectors have been produced and detector electronics is expected to be finished by mid-2013. The instrument control unit is undergoing extensive tests, to ensure full instrument functionality. Early results are promising and this paper discusses these H/W results, as well as some challenges encountered during the development of the instrument. © 2013 SPIE.

In preparation for future atmospheric space missions a consortium of Dutch organizations is performing design studies on a nadir viewing grating-based imaging spectrometer using OMI and SCIAMACHY heritage. The spectrometer measures selected species (O3, NO2, HCHO, H2O, SO 2, aerosols (optical depth, type and absorption index), CO and CH4) with sensitivity down to the Earth's surface, thus addressing science issues on air quality and climate. It includes 3 UV-VIS channels continuously covering the 270-490 nm range, a NIR-channel covering the 710-775 nm range, and a SWIR-channel covering the 2305-2385 nm range. This instrument concept is, named TROPOMI, part of the TRAQ-mission proposal to ESA in response to the Call for Earth Explorer Ideas 2005, and, named TROPI, part of the CAMEO-proposal prepared for the US NRC decadal study-call on Earth science and applications from space. The SWIR-channel is optional in the TROPOMI/TRAQ instrument and included as baseline in the TROPI/CAMEO instrument. This paper focuses on derivation of the instrument requirements of the SWIR-channel by presenting the results of retrieval studies. Synthetic detector spectra are generated by the combination of a forward model and an instrument simulator that includes the properties of state-of-the-art detector technology. The synthetic spectra are input to the CO and CH4 IMLM retrieval algorithm originally developed for SCIAMACHY. The required accuracy of the Level-2 SWIR data products defines the main instrument parameters like spectral resolution and sampling, telescope aperture, detector temperature, and optical bench temperature. The impact of selected calibration and retrieval errors on the Level-2 products has been characterized. The current status of the SWIR-channel optical design with its demanding requirements on ground-pixel size, spectral resolution, and signal-to-noise ratio will be presented.

Several organizations in the Netherlands are cooperating to develop user requirements and instrument concepts in the line of SCIAMACHY and OMI but with an increased focus on measuring tropospheric constituents from space. The concepts use passive spectroscopy in dedicated wavelength sections in the range of 300 to 2400 nm and wide angle, non-scanning, swath viewing. To be able to penetrate into the troposphere small ground pixels are used to obtain a fair fraction of cloud-free pixels and to allow precise detection of the sources of polluting gases. The trace gas products aimed for are O3, NO 2, HCHO, H2O, SO2, Aerosol (optical depth, type and absorption index), CO and CH4, covering science Issues on air quality and climate. The main challenge in the instrument design is to obtain a good signal-to-noise for cloud free pixels and for low ground albedo and light levels. Also the retrieval of separated tropospheric and stratospheric column amounts from a nadir looking instrument is challenging. The paper discusses the user requirements and compares alternative measurement strategies. It explains the selection of passive UV-Visible-NIR spectroscopy and comes with an instrument concept which provides the current best realisation of the user requirements.

The Global Ozone Monitoring Experiment (GOME) is a nadir-viewing spectrometer covering a broad wavelength range, from the UV to the near infrared. It has been operating since 1995 on board the ESA ERS-2 satellite, monitoring a large range of atmospheric trace constituents, with particular emphasis on ozone. The performance of the instrument is monitored in- flight by means of routine on-board calibration measurements, observing the sun and, occasionally, the moon. In this way, degradation of optical components in space can be monitored. For example, the performance of the broad-band detectors which monitor the polarization state of the incoming light is analyzed by means of solar measurements. The measurements of the polarization detector which samples UV light show a degradation of 6 percent per year. The optical components affected have been identified by monitoring the fractional polarization, which is a characteristic of the light back-scattered by the Earth's atmosphere. The influence of the observed degradation of Earth radiation measurements is estimated to be in the order of 1.5 percent per year in the UV wavelength range.

In-flight monitoring of the optical response of GOME revealed a number of instrumental features that drift or change with time. Some of these observed features are related to outgassing of the instrument in space. In particular outgassing of optical coatings, e.g. the dichroic mirror in GOME, can result in a change of the optical characteristics and thereby changing the response of the GOME instrument. Another feature is related to the etalon effect which results in a spectral modulation of the GOME spectra. This modulation varies in time due to a varying contamination layer, most likely ice, on the cooled detectors. Through the GOBELIN project the GOME breadboard model has been made available to us by ESA. The GOME breadboard model has been fully upgraded to represent the GOME flight mode and therefore offers a unique opportunity to study the above phenomenon under controlled laboratory conditions. First results are presented addressing in particular the effect of outgassing on instrument optical response, including the polarization response, and the etalon effect.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.