In-situ subsurface spectroscopy system for soil organic carbon measurement

Overview

S4 Mobile Laboratories is developing a modified version of its Subterra platform—Subterra Green—to provide rapid, in-situ measurement of soil organic carbon (SOC) content. The technology addresses a critical gap in the carbon credit market, where cost-effective verification of SOC is essential for scaling programs that incentivize carbon-sequestering land practices. By replacing traditional soil sampling and laboratory analysis with a mobile, push-probe spectroscopic system, the solution enables three-dimensional mapping of organic carbon to a depth of one meter in the field.

The system builds on S4's proven Subterra technology, which has been successfully demonstrated for forensic subsurface chemical detection. This proposal extends that foundation to agricultural and environmental applications, offering a faster, less disruptive, and more affordable approach to soil carbon quantification.

Technical specifications

• Push-probe fiber-optic spectroscopy: A portable probe is inserted directly into the soil, capturing visible and near-infrared spectra in situ without removing samples.
• Modified spectrometer and light source configuration: New spectrometers and illumination components are being integrated to optimize detection of soil organic carbon signatures.
• Chemometric analysis algorithms: Custom algorithms convert spectral data into accurate predictions of both gravimetric and volumetric SOC content, supported by insertion force data for bulk density estimation.
• Three-dimensional mapping: The mobile platform enables rapid spatial mapping of carbon content across depth profiles and across field areas.
• Field-portable design: The system is engineered for use by non-specialists under real-world field conditions, with emphasis on stable, repeatable results and minimal noise.

Technology readiness level

The underlying Subterra probe has been validated through working prototype construction and proof-of-concept studies demonstrating in-situ spectroscopic identification of chemical signatures in soil. The current proposal represents the adaptation of this proven platform to the specific challenge of soil organic carbon measurement. Future work focuses on iterative engineering to quantify and reduce measurement error and uncertainty, optimize the spectrometer-probe-light source system, and refine prediction algorithms. The goal is to achieve accuracy within acceptable limits for carbon credit verification and precision agriculture applications.