Hutengs Christopher, Ludwig Bernard, Jung András, Eisele Andreas, Vohland Michael
Geoinformatics and Remote Sensing, Institute for Geography, Leipzig University, Johannisallee 19a, 04103 Leipzig, Germany.
German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, 04103 Leipzig, Germany.
Sensors (Basel). 2018 Mar 27;18(4):993. doi: 10.3390/s18040993.
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.
中红外（MIR）光谱作为一种补充传统土壤分析的方法已受到广泛关注。鉴于有足够的光谱数据质量，最近可用的便携式MIR光谱仪还为现场应用提供了潜力。因此，我们将安捷伦4300手持式傅里叶变换红外光谱仪（漫反射光谱）与布鲁克Tensor 27台式仪器的性能进行了比较，比较内容包括：（i）通过小波分析量化的光谱质量和测量噪声；（ii）通过重复交叉验证分析对土壤有机碳（SOC）、总氮（N）、pH值、粘土和砂含量进行偏最小二乘法（PLS）校准的准确性；以及（iii）用蒙特卡罗光谱变量选择方法确定的这些土壤性质的关键光谱区域。手持式设备的测量和多变量校准与配备漫反射附件的布鲁克仪器一样好或略好，但不如用积分球收集的定向半球反射率（DHR）数据准确。噪声变化并未显著影响多变量PLS校准的准确性。确定的PLS校准关键光谱区域在安捷伦和布鲁克DHR数据之间提供了良好的匹配，特别是对于SOC和N。我们的研究结果表明，便携式傅里叶变换红外光谱仪是实验室中进行MIR测量的可行替代方案，并为现场应用提供了巨大潜力。
