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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Vol. 42, Iss. 6 — Feb. 20, 2003
  • pp: 1082–1090

Method for high-accuracy reflectance measurements in the 2.5-μm region

Rudolf Richter and Andreas Müller  »View Author Affiliations


Applied Optics, Vol. 42, Issue 6, pp. 1082-1090 (2003)
http://dx.doi.org/10.1364/AO.42.001082


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Abstract

Reflectance measurements with spectroradiometers in the solar wavelength region (0.4–2.5 μm) are frequently conducted in the laboratory or in the field to characterize surface materials of artificial and natural targets. The spectral surface reflectance is calculated as the ratio of the signals obtained over the target surface and a reference panel, yielding a relative reflectance value. If the reflectance of the reference panel is known, the absolute target reflectance can be computed. This standard measurement technique assumes that the signal at the radiometer is due completely to reflected target and reference radiation. However, for field measurements in the 2.4–2.5-μm region with the Sun as the illumination source, the emitted thermal radiation is not a negligible part of the signal even at ambient temperatures, because the atmospheric transmittance, and thus the solar illumination level, is small in the atmospheric absorption regions. A new method is proposed that calculates reflectance values in the 2.4–2.5-μm region while it accounts for the reference panel reflectance and the emitted radiation. This technique needs instruments with noise-equivalent radiances of 2 orders of magnitude below currently commercially available instruments and requires measurement of the surface temperatures of target and reference. If the reference panel reflectance and temperature effects are neglected, the standard method yields reflectance errors up to 0.08 and 0.15 units for 7- and 2-nm bandwidth instruments, respectively. For the new method the corresponding errors can be reduced to approximately 0.01 units for the surface temperature range of 20–35 °C.

© 2003 Optical Society of America

OCIS Codes
(120.4640) Instrumentation, measurement, and metrology : Optical instruments
(120.6780) Instrumentation, measurement, and metrology : Temperature
(120.6810) Instrumentation, measurement, and metrology : Thermal effects
(280.0280) Remote sensing and sensors : Remote sensing and sensors

History
Original Manuscript: August 6, 2002
Revised Manuscript: August 6, 2002
Published: February 20, 2003

Citation
Rudolf Richter and Andreas Müller, "Method for high-accuracy reflectance measurements in the 2.5-μm region," Appl. Opt. 42, 1082-1090 (2003)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-42-6-1082

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