SRON Netherlands Institute for Space Research will supply essential hardware for the infrared module of TROPOMI, the instrument onboard the European environmental satellite Sentinel-5 precursor, which shall monitor air pollution in the troposphere and climate change on earth, for example. On 9 December 2010, SRON concluded an agreement with the British space company Surrey Satellite Technology Limited (SSTL) to this effect. SRON will supply a specially developed combination of a prism and optical grating, which will be used in space for the first time, and the readout electronics for the advanced infrared detector. The space research institute is also responsible for testing and characterising the detector under space conditions.

In about 2014, the largely Dutch earth observation instruments OMI (onboard the NASA satellite EOS-AURA) and SCIAMACHY (onboard the ESA satellite Envisat) will have reached the end of their lifespans. Yet that does not mean an end to the prominent Dutch contribution to monitoring global air pollution and climate change. It is expected that a new Dutch Earth observation instrument will be launched into space at the end of 2014: TROPOMI, the Tropospheric Monitoring Instrument. TROPOMI is the only scientific instrument onboard the Sentinel-5 precursor satellite, a preparatory mission in the wide-ranging earth observation programme GMES from ESA and the European Commission.

TROPOMI combines the high resolution and the large field of view of OMI with the extensive wavelength range of SCIAMACHY. The main advantage is that TROPOMI can make far more detailed observations than its predecessors: the instrument will soon be able to identify the emission of air-polluting substances from individual towns and cities[DC1]. Furthermore, TROPOMI will be able to more accurately map the emission and distribution of air-polluting carbon monoxide as well as the sources and sinks of the particularly strong greenhouse gas methane. TROPOMI will also provide a wealth of information on the global water cycle. The Short Wave InfraRed module of TROPOMI (SWIR, see below) will be developed for these measurements.

New technology
TROPOMI is a so-called imaging absorption spectrometer. The instrument owes its considerable sensitivity to two technological innovations in the SWIR module.

SRON and TNO started on the development of a special immersion grating more than five years ago. This work was made possible by the financial support of the Netherlands Space Office (NSO). The immersion grating is a silicon grating illuminated from the inside: a specially developed combination of a prism and an optical grating that separates the radiation captured according to its wavelength. Thanks to these immersed gratings a drastic reduction in the size of the spectrometer is possible: a factor of 40 compared to conventional gratings. Indeed with conventional gratings the instrument would have been impossible to realise, in view of its size.

In addition to the immersed gratings, the SWIR module also contains an advanced detector for shortwave infrared radiation (SWIR), which satisfies the most stringent requirements. SRON is developing special electronics to control this detector and read its output. This combination of detector and electronics is being fully characterised by SRON so that later during the mission it will be possible to properly interpret the scientific data received.

Experimental set-up

The infrared detector, its readout electronics and the immersed gratings will to a large extent determine the scientific success of the mission. Therefore SRON first of all subjected these components to extensive testing in an experimental set-up. With the agreement signed on 9 December, the green light has been given for a development that must result in the actual production of flight models for these systems at the heart of the TROPOMI instrument, a phase that must be completed in just two years. The launch of the Sentinel-5 precursor mission with TROPOMI is planned for December 2014.

TROPOMI is a collaboration between KNMI, SRON, TNO and Dutch Space, on behalf of NSO. KNMI and SRON are responsible for the scientific management of the project. Dutch Space in Leiden is the principal contractor for the construction of the instrument. TROPOMI is funded in collaboration with ESA by the Ministry of Economic Affairs, Agriculture and Innovation, the Ministry of Education, Culture and Science and the Ministry of Infrastructure and the Environment