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Utilization of the internal soil standard method for the Brazilian soil spectral library: Spectral performance and proximate analysis

Romero, Danilo Jefferson, Dor, Eyal Ben, Demattê, José A.M., e Souza, Arnaldo Barros, Vicente, Luiz Eduardo, Tavares, Tiago Rodrigues, Martello, Mauricio, Strabeli, Taila Fernanda, da Silva Barros, Pedro Paulo, Fiorio, Peterson Ricardo, Gallo, Bruna Cristina, Sato, Marcus Vinicius, Eitelwein, Mateus Tonini
Geoderma 2017
Oxisols, analysis of variance, clay, clay fraction, databases, models, prediction, proximate composition, spectral analysis, spectrometers, tropical soils
There are several ways to extract much information using soil spectral data. For this reason, the database should be well built including standards and protocols both in the lab and in field acquisitions. If not all will align the measurement one to each other, the models will have no merit in term of large-scale application and stay as an academic exercise only. The use of standard samples with known spectra is expected to allow parameterizing mathematically soil spectra collected using different equipment and from distinct geometries. This study was proposed for the reason that to date, the new methodology proposed has not been evaluated in Brazilian tropical soils (Oxisols) in visible, near and short infrared (VIS-NIR-SWIR – 350 to 2500nm) spectral regions from three spectrometers (FieldSpec 3) in three distinct protocols (Long Light, Near Light and Contact Probe). Was compared the spectral intensity of each combination between spectrometer and protocols by ANOVA and the clay prediction capacity by PLSR with cross-validation, before and after the internal soil standard (ISS) method has applied. The results showed that visual spectral variation is minimized by the ISS method and the ISS correction enables better proxy modeling of clay content especially if the data are mixed from different protocols. The model for clay prediction is improved showing a favorable case to use the ISS technique in any soil spectral measurement for a better way to merge soil spectral libraries data from different sources.