Soil Moisture Effects on Portable X-ray Fluorescence Spectroscopy and Visible-Near Infrared Spectroscopy Measurements
Portable X-ray fluorescence (pXRF) and visible-near infrared spectroscopy (vis-NIR) are used to measure or predict soil properties such as soil organic carbon, nutrients, soil texture, and environmental pollutants such as heavy metals. These characteristics have great importance in soils under agriculture as well as environmental remediation. When taken in the field, vis-NIR and pXRF measurements are affected by the moisture conditions of the soil. This study seeks to quantify the effects of soil moisture on pXRF and vis-NIR measurements and propose correction equations of moisture effects. Topsoil and subsoil samples from an Entisol (~sand) and a Mollisol (~silty loam) were wetted in the laboratory to six different moisture contents and subsequently scanned by the pXRF and vis-NIR. The elemental intensity in spectra from the pXRF was significantly reduced by higher moisture contents, yielding lower elemental concentrations. This was linearly related to gravimetric water content. The effect was stronger in the silty loam soils than in the sandy soils. The reflectance of vis-NIR spectra decreased with increasing soil moisture content, and the reduction in reflectance of two spectral ranges (1410-1450 and 1910-1930 nm) was modeled by non-linear logarithmic regression. It is concluded that soil moisture reduces the measurements of pXRF and reflectance spectra of vis-NIR. The elemental concentrations measured by pXRF could be corrected by linear model with known gravimetric water content, whereas more sophisticated models are needed for vis-NIR spectra. The results of this study may improve the accuracy of pXRF and vis-NIR spectroscopy soil analysis used in the field, and could influence the way soil data is collected.
Authors: Sean Fischer | Alfred E. Hartemink | Yakun Zhang | Jenifer L. Yost
Spectral Evolution is a leading manufacturer of field-portable UV-Vis-NIR remote sensing spectroradiometers and spectrometers for applications including geological remote sensing, ground-truthing, spectral remote sensing, environmental and climate research, crop and soil research, vegetative studies, forestry and canopy studies, radiometric calibration transfer, upwelling and downwelling measurement and more. Our UV-Vis-NIR spectrometers and spectroradiometers provide the best combination of high resolution and high sensitivity resulting in the most precise field portable instruments available on the market.
Spectral Evolution UV-Vis-NIR spectroradiometers provide:
- Fast, full-spectrum UV-Vis-NIR measurements – 350-2500 nm with just one scan
- Superior reliability in the field with 100% diode array optics with no moving parts
- Wireless Bluetooth® Connection
- Lithium-ion rechargeable batteries for field use
- Lightweight and rugged
- Rugged handheld tablet for field use running DARWin™ LT on Windows 10 with digital camera, and GPS
- Field switchable optics for varying target sizes and measurement modes
All Spectral Evolution UV-Vis-NIR spectroradiometers include our exclusive DARWin™ SP Data Acquisition and Analysis software for one-touch, full range spectroscopic analysis of samples. DARWin™ SP automatically saves data as ASCII files for use with 3rd party software without post-processing.