Title: Preprocessing and calibration of optical diffuse reflectance signal for estimation of soil physical and chemical properties in the central USA Authors
|La, Woo-Jung - GYEONGSANG NATL U S KOREA|
|Chung, Sun-Ok - CHUNGNAM NATL U S KOREA|
|Kim, Hak-Jin - PUSAN NATL U S KOREA|
Submitted to: Journal of Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 2008
Publication Date: December 31, 2008
Citation: La, W.J., Sudduth, K.A., Chung, S., Kim, H.J. 2008. Preprocessing and calibration of optical diffuse reflectance estimation of soil physical and chemical properties in the central USA. Journal of Biosystems Engineering. 33(6):430-437. Interpretive Summary: Measuring the variation in soil properties within fields is an important component of precision agriculture. For many soil properties, it is difficult to obtain enough data to accurately characterize their spatial variation, due to the cost of traditional sampling and laboratory analysis. Sensors that can estimate soil properties without the need for sampling are a promising alternative. One technology that has received considerable attention in this regard is optical reflectance sensing in the visible and near infrared wavelength bands. Our goal in this study was to apply reflectance sensing to a set of soil samples from Missouri and Illinois and evaluate the results in comparison to standard laboratory methods. We found that optical reflectance sensing worked well to estimate a number of soil properties, including soil texture, organic matter, and cation exchange capacity (CEC). However, reflectance sensing did not provide good results for chemical properties – soil pH, phosphorus (P) and potassium (K). Thus, other approaches should be investigated for accurate estimates of soil chemical properties. These results will be useful to scientists and engineers developing or evaluating automated ways to measure soil properties, as they show that, over a broad range of soils, optical reflectance technology provided good estimates of soil physical properties but not of soil chemical properties.
Technical Abstract: Optical diffuse reflectance sensing in visible and near-infrared wavelength ranges is one approach to rapidly quantify soil properties for site-specific management. The objectives of this study were to investigate effects of preprocessing of reflectance data and determine the accuracy of the reflectance approach for estimating physical and chemical properties of selected Missouri and Illinois, USA surface soils encompassing a wide range of soil types and textures. Diffuse reflectance spectra of air-dried, sieved samples were obtained in the laboratory. Calibrations relating spectra to soil properties determined by standard methods were developed using partial least squares (PLS) regression. The best data preprocessing, consisting of absorbance transformation and mean centering, reduced estimation errors by up to 20% compared to raw reflectance data. Good estimates (r2 = 0.83 to 0.92) were obtained using spectral data for soil texture fractions, organic matter, and CEC. Estimates of pH, P, and K were not good (r2 < 0.7), and other approaches to estimating these soil chemical properties should be investigated. Overall, the ability of diffuse reflectance spectroscopy to accurately estimate multiple soil properties across a wide range of soils makes it a good candidate technology for providing at least a portion of the data needed in site-specific management of Korean agriculture.