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Proceedings Paper

Design of a full-hemispherical spectro-radiometer with high dynamic range for characterization of surface properties using multispectral BRDF data from VIS to NIR
Author(s): C. Hahlweg; H. Rothe
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Paper 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.

Paper Details

Date Published: 20 October 2005
PDF: 13 pages
Proc. SPIE 5965, Optical Fabrication, Testing, and Metrology II, 596519 (20 October 2005); doi: 10.1117/12.624832
Show Author Affiliations
C. Hahlweg, Helmut Schmidt Univ. (Germany)
H. Rothe, Helmut Schmidt Univ. (Germany)

Published in SPIE Proceedings Vol. 5965:
Optical Fabrication, Testing, and Metrology II
Angela Duparré; Roland Geyl; Lingli Wang, Editor(s)

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