One of the most difficult challenges in the future is to manage greenhouse effect and natural disasters. This requires spectroscopic imaging for remote sensing of greenhouse gases. The most known is the on-going ESA Anthropogenic CO2 monitoring mission (CO2M: Copernicus Space Component Expansion) that have been identified by the European Commission as a priority.
There are also needs for high-resolution earth observations in geological applications, land degradation studies, vegetation conditions, ground biomass or separation between snow, cloud & ice.
All these applications require a real-time monitoring from space. The core sensor of the current optical payload of these satellites is a HgCdTe N/P detector cooled to 150 K. This cryogenic temperature is a penalty which restricts its use. For many applications, the penalty is even greater when several small satellites must be used to deliver the required data.
SWIR imaging technologies are also widely used in airborne, laboratory and industry, via hyperspectral imaging systems. Example applications of SWIR hyperspectral imaging include mineral mapping, urban planning, quality control in food, military target detection, search and rescue, micro-plastic detection and classification, medical, and forestry.
The key technology common to SWIR satellites and hyperspectral imagers is the Focal Plane Arrays (FPA) of the imager. FPA, which is part of the hybrid circuit family is constituted of a detection circuit hybridized on a Read-Out Integrated Circuit (ROIC).
The small satellite European roadmap requires cheaper satellite. Then improvements within the detection circuit, especially for the SWIR bands, are necessary. To meet this objective, all SWIR camera integrators desire a detector technology capable of a higher operating temperature (HOT), as close as possible to room temperature: 240-290 K would be a convenient range which avoids the use of cooling system. Then, satellite power consumption and mass would be significantly decreased.
To increase the operating temperature, SWIRup project will concentrate on the improvement of the detection circuits, which are the common part of the FPAs.
The strategy selected for this project consists to push forward and to compare two sensor materials:
- Adapt the top state-of-the-art InGaAs III-V sensor material from 1,7µm to at least 2,3 µm, with a dark current level offering the possibility to operate the detector at the targeted temperature. This technology corresponds to InGaAs/GaAsSb super-lattice (type 2) lattice matched to InP substrate.
- Improve the HgCdTe P/N technology which is actually the European reference solution for SWIR detectors (see ASTEROID H2020 project).
The SWIRup consortium will develop, manufacture and test different detector prototype of the 2 technological chains identified previously with the goal to reach a TRL 5 level. At the end of the project, a system demonstration will be performed in Norway with an existing spectrometer to acquire realistic scenes in hyper spectral.
