Microwave Radiometer Measurements in Pfynwald

At the Pfynwald research site, L-band (1.4 GHz) and C-band (6.9 GHz) microwave radiometers are used to monitor the natural thermal microwave emission " referred to as brightness temperatures (BTs) " from the forest canopy. The instruments, developed by TerraRad, a WSL spin-off, are deployed in a unique setup that enables continuous upward- and downward-facing measurements from below and above the canopy, respectively. This configuration allows for the measurement of L- and C-band BTs under natural forest conditions, thereby advancing our understanding of the relationships between vegetation structure, vegetation water content (VWC), above-ground biomass (AGB), and the microwave emission and scattering processes that govern the observed BTs.

In combination with a wide range of environmental and physiological parameters collected at the site, these BT measurements offer valuable insights into forest ecophysiological processes. Furthermore, the BTs measured at the Pfynwald research platform serve as critical reference data for the development, calibration, and validation of retrieval algorithms used to derive e.g. Vegetation Optical Depth (VOD) from BTs measured by satellites such as the European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) mission. VOD, retrieved from spaceborne microwave radiometers, is known to correlate with key forest traits such as VWC and AGB, making it a powerful tool for large-scale assessments of vegetation dynamics.

In addition, Pfynwald is increasingly becoming a uniquely attractive site for space agencies such as the European Space Agency (ESA) - both for preparing future satellite missions and for improving retrieval algorithms used to interpret raw data from existing missions. This contributes to delivering more reliable information on large-scale changes in our forests, supporting both scientific research and societal decision-making.