Biliouris Dimitrios, Verstraeten Willem W, Dutré Phillip, Van Aardt Jan A N, Muys Bart, Coppin Pol
Katholieke Universiteit Leuven, Dept. of Biosystems, M3-BIORES, Celestijnenlaan 200E, BE-3001 Leuven, Belgium.
Katholieke Universiteit Leuven, Dept. of Computer Science, Celestijnenlaan 200A, BE-3001 Leuven, Belgium.
Sensors (Basel). 2007 Sep 7;7(9):1846-1870. doi: 10.3390/s7091846.
The design and calibration of a new hyperspectral Compact Laboratory Spectro-Goniometer (CLabSpeG) is presented. CLabSpeG effectively measures the bidirectionalreflectance Factor (BRF) of a sample, using a halogen light source and an AnalyticalSpectral Devices (ASD) spectroradiometer. The apparatus collects 4356 reflectance datareadings covering the spectrum from 350 nm to 2500 nm by independent positioning of thesensor, sample holder, and light source. It has an azimuth and zenith resolution of 30 and15 degrees, respectively. CLabSpeG is used to collect BRF data and extract BidirectionalReflectance Distribution Function (BRDF) data of non-isotropic vegetation elements suchas bark, soil, and leaves. Accurate calibration has ensured robust geometric accuracy of theapparatus, correction for the conicality of the light source, while sufficient radiometricstability and repeatability between measurements are obtained. The bidirectionalreflectance data collection is automated and remotely controlled and takes approximatelytwo and half hours for a BRF measurement cycle over a full hemisphere with 125 cmradius and 2.4 minutes for a single BRF acquisition. A specific protocol for vegetative leafcollection and measurement was established in order to investigate the possibility to extractBRDF values from Fagus sylvatica L. leaves under laboratory conditions. Drying leafeffects induce a reflectance change during the BRF measurements due to the laboratorySensors 2007, 7 1847 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.
介绍了一种新型高光谱紧凑型实验室光谱测角仪（CLabSpeG）的设计与校准。CLabSpeG使用卤光源和分析光谱设备（ASD）光谱辐射仪有效测量样品的双向反射因子（BRF）。该仪器通过独立定位传感器、样品架和光源，收集覆盖350纳米至2500纳米光谱的4356个反射率数据读数。其方位角和天顶角分辨率分别为30度和15度。CLabSpeG用于收集BRF数据，并提取树皮、土壤和树叶等非各向同性植被元素的双向反射分布函数（BRDF）数据。精确校准确保了仪器强大的几何精度，校正了光源的锥度，同时在测量之间获得了足够的辐射稳定性和重复性。双向反射数据收集是自动化且可远程控制的，对于半径为125厘米的全半球进行BRF测量周期大约需要两个半小时，单次BRF采集需要2.4分钟。为了研究在实验室条件下从欧洲山毛榉树叶中提取BRDF值的可能性，建立了特定的植被叶片采集和测量方案。由于实验室光源，干燥叶片效应在BRF测量期间会引起反射率变化。因此，一片叶子无法覆盖整个半球。相反，对于单个光源天顶角位置，每片叶子采集12次BRF测量，覆盖所有方位位置。数据以辐射度格式收集，反射率通过将叶片周期测量值除以Spectralon参考面板的辐射度周期来计算，再乘以Spectralon反射率校正因子和校正光源锥度效应的因子。给出了测量叶片的BRF结果。
