Mathematical techniques to remove moisture effects from visible–near-infrared–shortwave-infrared soil spectra—review 

Abstract

Visible–near-infrared–shortwave-infrared (VNIR–SWIR) spectroscopy is one of the most promising sensing techniques to meet ever-growing demands for soil information and data. To ensure the successful application of this technique in the field, efficient methods for tackling detrimental moisture effects on soil spectra are critical. In this paper, mathematical techniques for reducing or removing the effects of soil moisture content (SMC) from spectra are reviewed. The reviewed techniques encompass the most common spectral pre-processing and algorithms, as well as less frequently reported methods including approaches within the remote sensing domain. Examples of studies describing their effectiveness in the search for calibration model improvement are provided. Moreover, the advantages and disadvantages of the different techniques are summarized. Future research including further studies on a wider range of soil types, in-field conditions, and systematic experiments considering several SMC levels to enable the definition of threshold values for the effectiveness of the discussed methods is recommended.

Keywords:

• Soil moisture
• diffuse reflectance spectroscopy
• field-moist conditions
• algorithms
• indices

Disclosure statement

The authors report there are no competing interests to declare.

Notes

* The definition of spectral range differs from one community to another. In the soil proximal sensing community, the 400–2500 nm defines the VNIR range and the 2500–24000nm MIR range (sometimes TIR). The remote sensing community uses the definition that has a more physical basis relating to the detectors’ sensitivity and atmospheric attenuation, and denoting the visible range as 400–700 nm, NIR as 700–1000 nm and SWIR as 1000–2500 nm (also can be found as SWIR 1: 1000–1900 nm and SWIR 2: 1900–2500 nm), MWIR: 2500–5000 nm and LWIR: 900–1200 nm.

As this paper is more related to remote sensing, we used the “remote sensing” terminology through out the manuscript.

Additional information

Funding

This review was conducted as one of deliverables within ProbeField project funded in the framework of the H2020 European Joint Programme for SOIL.