Environmental Monitoring

Project SLIT

Double slit chip for the hyperspectral satellite EnMAP

Double slit chip
© Fraunhofer IMM

Double slit chip

EnMAP (Environmental Mapping and Analysis Program) is a German satellite mission that aims at monitoring and characterizing the Earth’s environmental and climate changes based on imaging spectroscopy. From its orbit at an altitude of approximately 650 km the ENMAP-satellite is supposed to record the light reflected from earth at an extremely large spectral bandwidth for every 30 x 30 m2 wide ground pixel. The five years mission is scheduled to be launched in the year 2018.


The broad wavelength range from 420 nm to 2420 nm, from the visible into the deep infrared region, requires to split up the spectral range on two spectrometers. In order to achieve the demanded ground resolution of up to 30 meters, especially the inlet openings of both instruments need to be positioned to one another at highest precision. In order to fulfill this essential requirement we have developed and manufactured a slit module using as a core element an ultra-precise double slit chip.

Properties and application areas

Although the slit chips are the most crucial components not only their optical properties have to be of adequate quality. Further components of the module such as the slit mount, the elements required for light deflection and scattered light suppression need to be fabricated from materials qualified for space applications such as aluminum, stainless steel, titanium and invar. The properties of these components need to be measured and documented precisely. The assembly of the slit module from the single components partially requires active mounting procedures in order to achieve a positioning accuracy below 5 µm.

Our research & development services

The quality management system established at our institute forms the basis for the quality documentation demanded by the contracting entity. In fact, the level required to comply by far exceeds the demands according to DIN ISO 9001. So far, we have developed and manufactured all components of the slit module meeting the required precision. At the same time we have been taking care that they show the necessary stability with respect to rocket launch and other possible shock loads. Coatings to achieve specific optical properties have been established and qualified. Herewith, we have implemented a first complete Engineering and Qualification Model (EQM) which has been successfully tested by the client OHB. Meanwhile we have realized a second EQM with optimized properties presently being in the final evaluation phase. In parallel to this the manufacturing of the final system to equip the ENMAP-satellite is running.