Assessment of Soil Organic Carbon using Hyperspectral UV-VIS-NIR Remote Sensing

Organic carbon (OC) is the primary energy source for microorganisms in soil. OC triggers nutrient availability for plant growth and plays a critical role in ecosystems. The total organic carbon (TOC) in soil affects color, nutrient capacity (cation and anion exchange capacity-CEC), nutrient stability and turnover, water relationships, aeration, cultivation, plant growth, and health. In the winter seasons, snow cover insulates and protects soil from deep frost. Deep frost can injure plant roots, alter the activity of the soil decomposer community, and cause problems with the TOC composition of the soil. Some abiotic factors, including global climate change and snow management processes by humans, can alter the snowpack and influence the dissolution and mineralization of TOC. These changes in the soil composition in winter can have dire effects on ecosystem processes during the spring growing season. This makes TOC a critical metric to study for environmental and agricultural scientists.

Measuring TOC provides information on soil fertility, aggregate stability, and the exchange of CO2 with the atmosphere. These characteristics are vital for climate research, and ecological applications including environmental monitoring and precision agriculture. TOC is often measured by dry combustion or wet oxidation. Both methods take a significant amount of sample preparation which can be costly and involves destruction of samples.
In recent years reflectance spectroscopy over the UV-VIS-NIR portion of the spectrum (350–2500nm) has become a fast and reliable tool for estimating soil organic carbon as well as many other parameters. By utilizing Spectral Evolution’s field instruments these improvements have the potential to bring a previously exclusively lab measurement to the field for a wide range of studies. This also allows for fast, accurate and cost-effective means of measuring TOC.

Components within a soil sample each have unique spectral signatures defined by reflectance or absorption as a function of wavelength. The primary absorption wavelengths regarding total organic carbon have been identified using different statistical methods. Typical soil samples show TOC absorption features between 400-570nm, 1434-1476nm, and 1819-2001nm. These bands range from the visible to the near infrared and so a full range instrument like the Naturaspec™ is preferable. The NaturaSpec is highly sensitive with a spectral resolution of 2.7nm@700nm, 5.5nm@1500nm, 5.8nm@2100nm making it well suited to measure the bands related to TOC. By using these wavelengths to train an algorithm it can be applied in the field and in the lab to determine TOC rapidly without destruction of the sample. Naturaspec is a full range, high resolution, hyperspectral spectroradiometer that is well suited to measure TOC in soils.

Soil conditions impact not only our planet’s ecosystem but also human infrastructure. Snow cover, or lack thereof, may significantly alter soil composition affecting food yield and other resources. Our earth is in a delicate state, and scientists must utilize non-destructive and timely alternatives for testing and research. High-resolution spectrometers, like the Spectral Evolution NaturaSpec™, allow users to collect lab-quality spectral scans in the field without sample preparation. The collected data provides a highly accurate analysis of soil composition, which can be quantitatively correlated to TOC. These rugged, battery-operated instruments utilize solid-state photodiode array detectors with no moving optical parts to ensure toughness and provide excellent stability and repeatability of measurement.

Spectral Evolution’s UV-Vis-NIR field-portable spectroradiometers are rugged and specifically designed for the challenges of environmental remote sensing. Our NIR spectroradiometers offer the best combination of high resolution and high sensitivity resulting in the most precise spectral data from any field instrument available on the market. The wide variety of accessories & fore optics make our instruments the most versatile spectroradiometers for all types of measurements, including reflectance, radiance, irradiance, & transmittance.