Quantitative soil spectroscopy

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Publisher: Hindawi Limited
Document Type: Editorial
Length: 1,925 words
Lexile Measure: 1710L

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Interest in the use of visible-near infrared reflectance spectroscopy for the determination of mineralogical composition in soils and planetary surfaces has been demonstrated since the 1970s with the development of databases of minerals spectra recorded in the laboratory by Hunt and Salisbury. A little later, in the early 1980s, the first spectral database (or library) of American soils was generated by Stoner and Baumgardner. In the mid-1980s, several workers demonstrated that different soil attributes could be estimated from the spectral reflectance measurement and the quantitative era of soil spectroscopy begun. The attractiveness of soil spectroscopy is that measurements are rapid and estimates of soil properties are inexpensive compared to conventional soil analyses. Nowadays, research on quantitative soil spectroscopy for the prediction of soil properties, prompted by developments in multivariate statistics and chemometrics, is continuing to grow. Over the past decades, the availability of new high signal-to-noise ratio hyperspectral sensors that can be mounted on airborne platforms or that can be used in the laboratory and the field opened significant new possibilities toward the quantitative analyses of the physical and biochemical composition of the Earth's soil.

The spectral reflectance of soil is a cumulative property that derives from the inherent spectral behaviour of heterogeneous combinations of minerals, organic matter, and water molecules in the soil. Studies on soil spectroscopy relate primarily to the following attributes. (i) Soil water, a key variable in hydrologic cycle, controls processes such as infiltration and discharge with consequences for plant growth, soil erosion, and land degradation. (ii) Soil carbon (content and composition), through its key role in the carbon cycle, is an important variable in global climate models. Soil organic matter, of which carbon is a major part, holds a large proportion of nutrients, cations, and trace elements that are needed for plant growth. (iii) Soil mineralogy and texture are important soil properties as they affect physical, chemical, and biological soil processes. Other soil parameters might also be estimated through either direct or indirect relationships of soil reflectance with the chemical, physical, and biological characteristics of the soil matrix.

In this regard, optical and infrared sensing covering the visible, infrared, and thermal parts of the electromagnetic spectrum, respectively, have shown good potential for retrieving information on soil attributes. Across this spectral range, three regions sensitive to soil properties can be defined as follows:

(i) The visible-near infrared (VNIR) spectral region from 0.4 to 1 [micro]m contains information on soil color, iron content and composition, soil water, and organic matter.

(ii) The near infrared (NIR) which also referred as the short-wave infrared (SWIR) in remote sensing from 1 to 2.5 [micro]m contains information on phyllosilicates, most sorosilicates, hydroxides, some sulphates, amphiboles, carbonates, soil water, and organic matter. A number of bench top and portable spectrometers combine the VNIR and the SWIR to provide spectra in the vis-NIR range from 0.4 to 2.5 [micro]m.

(iii) The mid-infrared (mid-IR), which...

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Gale Document Number: GALE|A369914513