A Hardened CO$_2$ Sensor for In-Ground Continuous Measurement in a Perennial Grass System

TL;DR

This work presents a hardened in-ground $CO_2$ sensor (Hedorah-NDIR) designed for continuous subsurface monitoring in perennial grass systems under winter ice encasement. The core approach replaces a conventional eCO2 sensor with a rugged $CO_2$-specific NDIR module ($SCD30$), integrated into a minimal PCB, and housed in a two-part, gas-diffusive nylon enclosure with Gore-Tex vents and a detachable M12 connector for field maintenance. Field deployments over multiple seasons demonstrate robust performance across a wide $CO_2$ range with minimal data loss, while laboratory tests characterize a rapid response (time constant ≈ $7$ minutes) and predictable steady-state behavior within the sensor's accuracy. The resulting system enables dense spatial-temporal data collection essential for understanding ice encasement damage and winterkill in turfgrass, with broader applicability to other subsurface CO$_2$ monitoring needs.

Abstract

Carbon dioxide levels below the soil surface are an important measurement relating to plant health, especially for plants such as perennial grasses in northern climates where ice encasement can occur over winter. In such cases, the CO$_2$ levels can build up and become toxic. This is likely a significant contributor to turfgrass death over winter; however, there is an insufficient amount of data regarding this phenomenon in large part due to the lack of effective sensors. Many off the shelf CO$_2$ sensors exist, but they are not sufficiently hardened for in ground deployment over winter. As a result, the only options currently available are very costly automated gas samplers or manual sampling at intervals with laboratory testing -- a process that results in a limited number of data points and is labor intensive. To combat this problem we have taken an established NDIR CO$_2$ sensor and hardened it for use in winter and ice encased environments to allow for continuous automated sampling of subsurface CO$_2$ levels to better understand ice encasement damage in perennial grass systems.

Figures (6)

• Figure 1: Block diagram of Hedorah sensor
• Figure 2: Renders of various sensor enclosure views
• Figure 3: Diagram cup cut to insert sensor
• Figure 4: Example below ground CO2 sensing over the course of a winter season
• Figure 5: Example of field installation of CO2 sensor