The benefits of soil temperature monitoring

Why is it important to monitor ground temperature? The ground is affected in many ways without us ever noticing. It is important to have a clear picture of ground temperature for the top 1 to 3m for many engineering and biological reasons. For instance, it is necessary for many construction projects that include the design of airports and road pavements, the excavation of foundations, the depth at which service pipes should be laid to avoid freezing, soil decay rates, plant health and phenology, invertebrate studies, the monitoring of compost and quantifying seepage movement in canals and waterways.

The main factors that determine the temperature of the ground are meteorological, terrain and subsurface variables.

Meteorological elements influence surface and subsurface temperature by affecting the rate at which heat is transferred to or from the atmosphere and the ground. The main elements are solar radiation and air temperature. Solar radiation is the single most important factor. Other meteorological factors such as wind or rain can cause significant local variations. Snow is also an important factor affecting ground temperature. Snow has insulating properties, but it also provides a lot of moisture during thaw season.

Terrain has also an effect. In dense vegetation areas, foliage can also provide an insulating effect, protecting the ground from weather extremes, blocking heat transfers to and from the atmosphere.

Subsurface variables that determine its response to temperature changes at the surface are volumetric heat capacity, thermal conductivity, latent heat (the heat required to freeze or thaw a unit volume of frozen soil) and water content. The ratio, K/C (K being volumetric heat capacity, and C being thermal conductivity), known as thermal diffusivity, is important in calculating rate of heat flow in the ground.

Water is also a determining factor. As heat capacity, thermal conductivity and latent heat depend on it, they also are codependent. the larger the water content, the larger the heat capacity, thermal conductivity, and latent heat.

Temperature as a fundamental determinant

Since temperature is a constant factor, it also becomes a powerful tool for analysis. Using multi sensor temperature data loggers to track and log temperatures at predetermined depths, can give the researcher valuable insight in many spheres of activity.

Soil health:

by comparing the temperature at different levels from site A with the temperature at different levels from site B can suggest the best placement for root and foliage growth, subsurface biodiversity, freezing depths, snow thaw dynamics, etc.

Soil porosity:

when planning excavation or construction project, knowing the temperature starts can determine if the terrain is stable from movement, if the drainage will require attention, the depth for installing pipes.

Soil mineral movement:

temperature at different soil levels can also give an idea on different mineral movement within the ground. Minerals absorb or repulse heat and radiation. So, by logging very small variations, one can determine what the composition is and where they move.

Compost monitoring:

By monitoring temperature at different levels in a compost installation, agents can know if the breakdown of bio composable material is working. As these materials breakdown, heat is released and can be recorded. Know if activity has slowed or not, will allow the response of turning the soil, or adding more green or dry substrate.

Quantifying seepage in irrigation canals and in riverbeds:

Ramon Naranjo for USGS in Nevada, uses multi sensor temperature data loggers (T.rod.X) to quantify water movement in irrigation canals. They are able to record and trace water loss and mineral movement throughout the irrigation canal and mitigate water loss. This is how Mr. Naranjo put it:

“We use temperature data to describe the rate and direction of water flow through sediments beneath rivers and along the shoreline of lakes. In manmade structures like irrigation canals, the use of this data can provide estimates of seepage losses that can help water managers make decisions to make improvements that will lead to more efficient use of water.”

Temperature has been a determining factor in ground research for many years and has allowed researchers to understand the many variables that make up the ground we walk on. It has also allowed government, business, and academia to make better decisions and innovate. Innovations using multi sensor temperature data loggers have accelerated as technology advances. “Before the TROD, we didn’t have the technology to measure sediment temperatures without expensive dataloggers and batteries. The measurement approach has advanced with the TROD through a combination of small self-logging temperature logging sensors and rugged materials that could be left in place while logging. The low profile of the probe also means that debris carried by the currents would not interrupt the data, shift the sensors, or result in damage. This made improvements to making measurement during floods, in urbans settings and in environments where equipment might get tampered with by the public” said Ramon.

“The capabilities of the TRODX could be advanced by including the specific conductance so the probe can be used with tracer experiments. Also, integrating analytical methods within the Weebutton software to automatically provide estimates of flux rates could simplify the analysis and provide near real-time flow estimates.” These kinds of advances are already in the R&D pipeline and will surely contribute to the understanding of ground science.