Compact Spectrometers for Earth Observation

Abstract

Driven by technology developments triggering end user’s attention, the market for nano- and microsatellites is developing rapidly. At present there is a strong focus on 2D imaging of the Earth’s surface, with limited possibilities to obtain high resolution spectral information. More demanding applications, such as monitoring trace gases, aerosols or water quality still require advanced imaging instruments, which tend to be large, heavy and expensive. In recent years TNO has investigated and developed several innovative concepts to realize advanced spectrometers for space applications in a more compact and cost-effective manner. This offers multiple advantages: a compact instrument can be flown on a much smaller platform (nano- or microsatellite); a low-cost instrument opens up the possibility to fly multiple instruments in a satellite constellation, improving both global coverage and temporal sampling; a constellation of low-cost instruments can provide added value to the larger scientific and operational satellite missions. Application of new technologies allowed us to reduce the instrument size significantly, while keeping the performance at a sufficient level. Low-cost instruments may allow to break through the ‘cost spiral’: lower cost will allow to take more development risk and thus progress more quickly. This may lead to a much faster development cycle than customary for current Earth Observation instruments. This new development approach is demonstrated using the most advanced design of a hyperspectral imaging spectrometer (named ‘Spectrolite’) as an example. Several different novel design and manufacturing techniques were used to realize this compact and low-cost design. Laboratory tests as well as the first preliminary results of airborne measurements with the Spectrolite breadboard will be presented. The design of Spectrolite offers the flexibility to tune its performance (spectral range, spectral resolution) to a specific application. Thus, based on the same basic system design, Spectrolite offers a range of applications to different clients. To illustrate this, we present a mission concept to monitor NO₂ concentrations over urban areas at high spatial resolution, based on a constellation of small satellites.