Sven-Erik Sandström

Research

Radar measurement for estimation of biomass in forest stands

An estimate of the biomass in a forest stand can be obtained from satellite data. There are also optical methods that measure the individual tree and thus replace manual measurement.

Ground based methods that measure along a path are a compromise in terms of capacity and accuracy. The method considered here is based on the change in the propagation of electromagnetic waves that takes place when the waves pass through a forest. This corresponds to the relation that is known as Fermat's principle. Through accurate measurements, differences in the detected distance can be used as an indication of the biomass in a stand.

For this, portable broadband antennas are used in combination with software radio techniques. The concept relates to replacing electronics by software in a computer. This makes it possible to do signal processing in a USRP module without having to design electronic circuits.

The method has been developed for a couple of years and can now be used in the field. The principle, in simple terms, is that the distance between the antennas is measured with the FMCW method, a form of frequency modulation. The measurements detect small differences in distance that depend on the properties of the forest. A thick forest produces a larger difference in distance while a thin, sparse forest produces a smaller difference.