Spectro-Gonio Radiometer

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This spectro-gonio radiometer has been specially designed to measure with a high photometric accuracy the bidirectional reflectance of bright planetary materials over most of the solar spectrum and under wide illumination/observation configurations.

Location: Institut de Planétologie et Astrophysique de Grenoble CNRS - Université Grenoble Alpes Saint Martin d’Hères, France

Persons in charge: - Scientific : Bernard Schmitt, Research director - Technical : Olivier Brissaud, Engineer

- Type: Laboratory Experiment facility

Spectral range : 0.3 - 4.5 µm (-> 5.0 µm: lower S/N) (4.2-4.3µm: atm. CO2 limited) Spectral resolution : variable - mini : < 0.1 nm (but S/N limited) - maxi : 6 nm (<750nm), 12 nm (<1500nm), 24 nm (<3000nm), 48nm (>3000nm)

Bidirectional Reflectance - Incidence angle : 0° to 85° resolution: 0.1° maximum sampling : 0.1° - Emergence angle : 0° to 80° (to 83° for dark / fine grained samples) resolution : ± 2° (may be reduced to < ± 0.5°, but S/N limited) max. sampling : 0.1° - Azimuth angle : 0° to 180° resolution : ± 2° (may be reduced to < ± 0.5°, but S/N limited) max. sampling : 0.1° - Phase angle : mini to 165° mini : ~ 8° for bright / large grained samples ~ 4° for dark / fine grained samples

- Illumination diameter (nadir) : 200 mm - Observation diameter (nadir) : 20 mm


Photometry : absolute: 0.3-1.0 µm: better than 1% over all configurations

                       (relative to a calibrated Spectralon 0.99 reference panel) 

1.0-2.5 µm: better than 1% over all configurations 2.5-5 µm : better than 2% over all configurations relative : better than 0.5% (0.3-2.5 µm)

Polarimetry options (only partly tested) - Illumination : linear polarization : variable 0 to 90° spectral range : 0.3 - 2.8 µm - Observation : 1 component over the 0.3 - 5µm range + unpolarized or || and ┴ components over restricted spectral range

Samples - Types: rocks, minerals, snow / ice, sulfur, ... (from very bright to dark) - Texture: compact or granular - Grain size: micrometer to a few millimeters - Size: maxi: 300mm diameter, 250 mm deep (bright & coarse grained samples) 120 mm in diameter, 2-10 mm deep (dark or fine grained samples) mini: 25 mm x 120 mm (for principal plane observation down to 80°) 25 mm x 45 mm (for principal plane observation down to 60°) Temperature: room temperature or heated down to -20°C (in cold room) down to -40°C (in SERAC environmental cell)


Experiment control: PC/Windows, fully software controlled (LabView©).

                               automatic acquisition of all spectral/geometric configurations

Acquisition time: typical 15 mn for 200 spectral channels in visible (S/N dependent) total : 15 hours for 100 spectral channels and 100 geometries

Current state of system: 0.3 - 5 µm range : fully calibrated polarization : tested -> 2003 low temperature : tested in cold room down to -20°C [[ Availability to community]]: Technical improvements/calibration (20%) LPG + associated laboratories measurements (60%) open to specific collaborations w. funding (20%)

References: Bonnefoy, N., O. Brissaud, B. Schmitt, S. Douté, M. Fily, W. Grundy, and P. Rabou 2000. Experimental system for the study of planetary surface materials’ BRDF. Remote Sensing. Rev., 19, 59-74.

Bonnefoy, N. 2001. Développement d’un spectrophoto-goniomètre pour l’étude de la réflectance bidirectionnelle des surfaces géophysiques. Application au soufre et perspectives pour le satellite Io. PhD Thesis, LPG - Université Joseph Fourier, Grenoble (20/11/2001).

Brissaud, O., B. Schmitt, N. Bonnefoy, S. Douté, P. Rabou, W. Grundy, and M. Fily 2004. Spectrogonio radiometer for the study of the bidirectional reflectance and polarization functions of planetary surfaces: I. Design and tests. Appl. Optics, 43 (9), 1926-1937.

Pommerol, A., and B. Schmitt 2008. Strength of the H2O near-infrared absorption bands in hydrated minerals: Effects of particle size and correlation with albedo. J. Geophys. Res E, 113, E10009 [doi:10.1029/2007JE003069]

Pommerol, A., and B. Schmitt 2008. Strength of the H2O near-infrared absorption bands in hydrated minerals: Effects of measurement geometry. J. Geophys. Res E, 113, E12008 [doi: 10.1029/2008JE003197].

Pommerol, A., Schmitt B., Beck, P., Brissaud, O. 2009. Water sorption on Martian regolith analogs: thermodynamics and near-IR reflectance spectroscopy. Icarus soumis


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