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Sensors 2018, 18(4), 993; https://doi.org/10.3390/s18040993

Comparison of Portable and Bench-Top Spectrometers for Mid-Infrared Diffuse Reflectance Measurements of Soils

1
Geoinformatics and Remote Sensing, Institute for Geography, Leipzig University, Johannisallee 19a, 04103 Leipzig, Germany
2
German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, 04103 Leipzig, Germany
3
Deparatment of Environmental Chemistry, Kassel University, Nordbahnhofstr. 1a, 37213 Witzenhausen, Germany
4
Technical Department, Szent István University, Villányi út 29-43, 1118 Budapest, Hungary
5
SphereOptics GmbH, Gewerbestrasse 13, 82211 Herrsching, Germany
*
Author to whom correspondence should be addressed.
Received: 3 March 2018 / Revised: 24 March 2018 / Accepted: 25 March 2018 / Published: 27 March 2018
(This article belongs to the Section Physical Sensors)
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Abstract

Mid-infrared (MIR) spectroscopy has received widespread interest as a method to complement traditional soil analysis. Recently available portable MIR spectrometers additionally offer potential for on-site applications, given sufficient spectral data quality. We therefore tested the performance of the Agilent 4300 Handheld FTIR (DRIFT spectra) in comparison to a Bruker Tensor 27 bench-top instrument in terms of (i) spectral quality and measurement noise quantified by wavelet analysis; (ii) accuracy of partial least squares (PLS) calibrations for soil organic carbon (SOC), total nitrogen (N), pH, clay and sand content with a repeated cross-validation analysis; and (iii) key spectral regions for these soil properties identified with a Monte Carlo spectral variable selection approach. Measurements and multivariate calibrations with the handheld device were as good as or slightly better than Bruker equipped with a DRIFT accessory, but not as accurate as with directional hemispherical reflectance (DHR) data collected with an integrating sphere. Variations in noise did not markedly affect the accuracy of multivariate PLS calibrations. Identified key spectral regions for PLS calibrations provided a good match between Agilent and Bruker DHR data, especially for SOC and N. Our findings suggest that portable FTIR instruments are a viable alternative for MIR measurements in the laboratory and offer great potential for on-site applications. View Full-Text
Keywords: portable FTIR spectrometer; mid-infrared soil spectroscopy; benchmarking; noise analysis; continuous wavelet transform; multivariate calibration; partial least squares; spectral variable selection portable FTIR spectrometer; mid-infrared soil spectroscopy; benchmarking; noise analysis; continuous wavelet transform; multivariate calibration; partial least squares; spectral variable selection
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Hutengs, C.; Ludwig, B.; Jung, A.; Eisele, A.; Vohland, M. Comparison of Portable and Bench-Top Spectrometers for Mid-Infrared Diffuse Reflectance Measurements of Soils. Sensors 2018, 18, 993.

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