A Compact Laboratory Spectro-Goniometer (CLabSpeG) to Assess the BRDF of Materials. Presentation, Calibration and Implementation on Fagus sylvatica L. Leaves

Sensors

Dimitrios Biliouris²  Willem W. Verstraeten²  Phillip Dutré⁴  Jan A.N. van Aardt³  Bart Muys¹ 

[1] Katholieke Universiteit Leuven, Dept. of Land Management and Economics, Celestijnenlaan 200E, BE-3001 Leuven.;Katholieke Universiteit Leuven, Dept. of Biosystems, M3-BIORES, Celestijnenlaan 200E, BE-3001 Leuven.;Council for scientific and Industrial Research (CSIR) Natural Resources and the Environment – Ecosystems Earth Observation, P.O.Box 395, 0001 Pretoria, South Africa.;Katholieke Universiteit Leuven, Dept. of Computer Science, Celestijnenlaan 200A, BE-3001 Leuven.

关键词: BRDF-retrieval;    BRF-measurement;    multi-angular;    hyperspectral;    spectroradiometer;    vegetation;    heat-stress;   

DOI  :  10.3390/s7091846

来源: mdpi

【 摘 要 】

The design and calibration of a new hyperspectral Compact Laboratory Spectro-Goniometer (CLabSpeG) is presented. CLabSpeG effectively measures the bidirectional reflectance Factor (BRF) of a sample, using a halogen light source and an Analytical Spectral Devices (ASD) spectroradiometer. The apparatus collects 4356 reflectance data readings covering the spectrum from 350 nm to 2500 nm by independent positioning of the sensor, sample holder, and light source. It has an azimuth and zenith resolution of 30 and 15 degrees, respectively. CLabSpeG is used to collect BRF data and extract Bidirectional Reflectance Distribution Function (BRDF) data of non-isotropic vegetation elements such as bark, soil, and leaves. Accurate calibration has ensured robust geometric accuracy of the apparatus, correction for the conicality of the light source, while sufficient radiometric stability and repeatability between measurements are obtained. The bidirectional reflectance data collection is automated and remotely controlled and takes approximately two and half hours for a BRF measurement cycle over a full hemisphere with 125 cm radius and 2.4 minutes for a single BRF acquisition. A specific protocol for vegetative leaf collection and measurement was established in order to investigate the possibility to extract BRDF values from Fagus sylvatica L. leaves under laboratory conditions. Drying leaf effects induce a reflectance change during the BRF measurements due to the laboratory illumination source. Therefore, the full hemisphere could not be covered with one leaf. Instead 12 BRF measurements per leaf were acquired covering all azimuth positions for a single light source zenith position. Data are collected in radiance format and reflectance is calculated by dividing the leaf cycle measurement with a radiance cycle of a Spectralon reference panel, multiplied by a Spectralon reflectance correction factor and a factor to correct for the conical effect of the light source. BRF results of measured leaves are presented.

【 授权许可】

Unknown   
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