GNSS measurements in Pfynwald

As part of the ESA-funded RISOTTO project (Reference data for Improved SAR-based fOresT waTer Observations), several Global Navigation Satellite System (GNSS) receivers are being installed above and below the forest canopy at the Pfynwald test site. Differences in the strength of GNSS signals (1.1 -1.6 GHz) measured at these two levels provide insights into the attenuation of microwave radiation as it passes through the canopy, thereby enabling continuous monitoring of forest canopy water content at multiple locations.

At the Pfynwald research site, comparative measurements are also being conducted for the first time using below canopy upward- and above canopy downward-facing microwave radiometers operating at L-band (1.4 GHz) and C-band (6.9 GHz). This unique combination of quasi-active GNSS measurements together with purely passive microwave radiometer measurements (brightness temperatures) yields valuable insight to enhance our understanding of the complementary information provided by active- and passive microwave remote sensing systems.

The spatially and temporally co-located GNSS and radiometer data enable the refinement of models describing microwave propagation across forest canopies. This in turn makes a critical contribution to improving remote sensing methods aimed at large-scale assessments of key forest variables, such as Above-Ground Biomass (AGB) and Vegetation Water Content (VWC).

By employing these novel remote sensing techniques (GNSS and microwave radiometry), we aim to establish Pfynwald not only as a hotspot for addressing forest physiological research questions, but also as an attractive research and validation site for space agencies such as the European Space Agency (ESA)