Testing sensors for validating microwave products of forest water status

European forests are experiencing a significant increase in mortality as a result of plagues and wildfires, often enhanced by droughts. Understanding, managing, and adapting our forests to future changes requires large-scale spatiotemporal monitoring of forest water status. Microwave remote sensing products, such as Vegetation Optical Depth (VOD), are a valuable addition to optical metrices due to their direct relationship to vegetation water content (VWC) and consistent time series. These products are increasingly used for studying drought-stressed vegetation. However, unlike soil moisture, there is little continuous ground-based data to validate VWC estimates from microwave instruments. To accelerate the development of VWC products, we need continuous ground-based measurements for various locations. In a Dutch coniferous forest, we have tested state-of-the-art sensors and approaches to measure water content and potential continuously (i.e. using frequency- and time domain reflectometers, GNSS receivers, microtensiometers, dielectric leaf wetness sensors, sap flow sensors, dendrometers). The objectives are (I) to perform long-term continuous measurements, (II) to use our insights to scale up the measurements to other locations. After multiple months of measuring, we here present our first results.