L-band Observations of Soil and Trees in Freezing/Thawing Conditions – LOSTinFTC

Living Planet Fellowship research project carried out by Anna Kontu.

Passive microwave observations at L-band (1.4 GHz) can detect soil freeze/thaw status based on the differences in the electrical properties of ice and liquid water. This method is suitable for detecting autumn freezing, but during spring thawing the liquid water in melting snow confounds the signal from soil; however, the penetration depth of electromagnetic waves at L-band may allow limited retrieval of information from subnivean soils even in snowmelt conditions. Another source of inaccuracy in present F/T retrievals is the liquid water in trees; while the water in soil mostly freezes when the soil temperature drops below 0 °C, the water in trees can stay in liquid form down to -40 °C. The amount of liquid water and ice in trees affects the transmissivity of forests and hence the transmissivity of forests is dependent on temperature.

Finnish Meteorological Institute’s Arctic Space Centre (FMI-ARC) in Sodankylä, Finland, hosts a measurement setup, including two ESA ELBARA-II L-band radiometers, which could be used to study both the transmissivity of boreal coniferous forest and detection of soil thawing when snow is melting. The existing infrastructure allows for measurements from above and below the forest, and reference measurements monitor soil, snow and vegetation properties, including snow wetness and tree dielectric permittivity, among other parameters.

This project aims to develop a model for boreal forest transmissivity dependence on temperature and to study possibilities for detecting soil thawing during spring snowmelt.