Check-in: moisture content – radiowave arrival measurement on roundwood and chip trucks

Stacked roundwood moisture content – fast and non-destructive

Knowing how much moisture is present in roundwood is important – it affects both the value of the raw material and its processability, for example as biofuel. However, today there is a lack of efficient and reliable methods for measuring moisture content in roundwood, especially when the wood is stacked in piles.

In the project “Check-in: Moisture Content”, researchers investigated whether microwaves – like those used in microwave ovens – can be used to measure moisture content directly through stacks of pine and spruce logs. The results show that this is possible: signals can be sent through the stack and within minutes produce measurement values that correlate with how moist the wood is.

A model was developed to translate measurement data into moisture content, with an accuracy of approximately ±4 percentage points for unfrozen wood. This is comparable to, or could eventually surpass, today’s manual sampling methods, which are both time-consuming and labor-intensive. For the measurements, it is advantageous to know something about the diameter of the logs, for example via photos taken during remote imaging measurement.

The study showed that the microwave technique is more complex for whole logs than for chopped materials such as wood chips. There are several reasons for this: the size of the logs affects how the microwaves propagate, stacks contain unevenly distributed air, and it is difficult to establish an exact reference value for the log moisture content. Some of these challenges could be addressed by switching to a lower microwave frequency than the one tested in the study.

What do the results mean in practice?

If the method is further developed, it could offer major benefits:

• Faster measurements directly on trucks, at industrial sites, or at terminals
• Better decision-making support for trade, storage, and energy production
• More efficient bioenergy systems, where fuel quality can be optimized in real time
• Potential to trade roundwood based on dry weight, which better reflects energy and fiber content

The project shows that microwave technology is a promising path forward for digitizing and streamlining the handling of forest raw materials. With more measurements and improved models across different temperature ranges, the method could become an important tool in future forestry and energy systems.