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The Compact High Resolution Imaging Spectrometer (CHRIS), to be launched on board the PROBA (Project for On-Board Autonomy) satellite in 2001/2002, will provide remotely-sensed data for terrestrial and atmospheric applications. The mission is intended to demonstrate the potential of a compact, low-cost, imaging spectrometer when combined with a small, agile satellite platform. CHRIS will provide data in 18-62 user-selectable spectral channels in the range 400 nm to 1050 nm (1.25 nm -11 nm intervals) at a nominal spatial resolution of either 25 m or 50 m. Since PROBA can be pointed off-nadir in both the along-track and across-track directions, it will be possible to use CHRIS to sample the Bidirectional Reflectance Distribution Function (BRDF) of the land surface. This combination of an agile satellite and a highly configurable sensor offers the unique potential to acquire high spatial resolution, spectral BRDF data sets and, from these, to study the biophysical and biochemical properties of vegetation canopies. It will also provide an important means of validating similar data sets from other, coarser spatial resolution sensors, such as VEGETATION, POLDER2, MODIS and MISR. This paper presents key features of the instrument, and explores the potential of CHRIS for estimating canopy biophysical parameters from space by means of a LUT-based BRDF model inversion scheme.

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Abstract.A breadboard demonstrator of a novel UV/VIS grating spectrometer has been developed based upon a concentric arrangement of a spherical meniscus lens, concave spherical mirror and curved diffraction grating suitable for a range of atmospheric remote sensing applications from the ground or space. The spectrometer is compact and provides high optical efficiency and performance benefits over traditional instruments. The concentric design is capable of handling high relative apertures, owing to spherical aberration and comma being near zero at all surfaces. The design also provides correction for transverse chromatic aberration and distortion, in addition to correcting for the distortion called "smile", the curvature of the slit image formed at each wavelength. These properties render this design capable of superior spectral and spatial performance with size and weight budgets significantly lower than standard configurations. This form of spectrometer design offers the potential for exceptionally compact instrument for differential optical absorption spectroscopy (DOAS) applications from LEO, GEO, HAP or ground-based platforms. The breadboard demonstrator has been shown to offer high throughput and a stable Gaussian line shape with a spectral range from 300 to 450 nm at 0.5 nm resolution, suitable for a number of typical DOAS applications.

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