20 October 2005 Design of a full-hemispherical spectro-radiometer with high dynamic range for characterization of surface properties using multispectral BRDF data from VIS to NIR
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Abstract
In further development of an existing semi-hemispherical spectro-radiometer without moving parts for angular resolution based on an elliptical mirror, a full-hemispherical device was designed. For the purpose of cost reduction and reproducibility it was decided to switch from the formerly used log-polar sensor to a commercially available cartesian CMOS camera with a dynamic range of 112dB. The sensor consists of 322096 pixels, producing an equivalent angle resolution. The system can take up to 53 full-hemispherical BRDFs per second. Illumination is provided by a set of assorted LEDs. A radiometric measurement over a wide spectral range from VIS to NIR requires a pixelwise calibration taking into account the spectral characteristics of the light source, filters, elliptical mirror and the CMOS-detector itself. However, the most important problems during calibration are the spectral response of the CMOS-detector, as well as its sensitivity as a function of the angle of the incident light. Also the elliptical mirror has a reflectivity which is a function of the incident angle, the wavelength and polarization of the collected light. All these influences have to be taken into account, if a proper radiometric measurement shall be conducted. The paper deals with the instrument design, the calibration procedures and gives some measurement results.
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C. Hahlweg, C. Hahlweg, H. Rothe, H. Rothe, } "Design of a full-hemispherical spectro-radiometer with high dynamic range for characterization of surface properties using multispectral BRDF data from VIS to NIR", Proc. SPIE 5965, Optical Fabrication, Testing, and Metrology II, 596519 (20 October 2005); doi: 10.1117/12.624832; https://doi.org/10.1117/12.624832
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