A novel in-situ monitoring technology for hard-to-reach forests supporting EO land product validation

Forests play a key role in the Earth climate system. However, the extent and severity of climate change impacts remain uncertain due to the lack of in-situ data, particularly in hard-to-reach areas characterized by strong logistical limitations. Recent advances in Internet of Things (IoT) technologies, satellite connectivity, and energy harvesting systems are opening new opportunities for the deployment of autonomous in-situ monitoring devices in standalone configurations. The aim of the Horizon Europe RemoTrees project is to design and develop an innovative, autonomous in-situ monitoring system tailored for remote forest environments, capable of transmitting data via satellite communication to a dedicated platform. Within this framework, RemoTrees enables the in-situ measurement of up to four Essential Climate Variables (ECVs), including the fraction of Absorbed Photosynthetically Active Radiation (fAPAR), Leaf Area Index (LAI), soil moisture, and above-ground biomass change. Additional variables such as stem growth, stem moisture, sap flow, canopy transmittance, and meteorological parameters are also acquired. RemoTrees, thus, aims to strengthen the Copernicus in-situ component, supporting the calibration and validation of Earth Observation (EO) products. This work presents preliminary results based on RemoTrees (RT) data collected at Level 1 (L1) sites, where the system is currently being tested prior to deployment at Level 2 (L2) sites worldwide. The analysis focuses on spectral measurements acquired above and below the canopy using the cyberRadiation, cyberTrunk and cyberSoil devices. Canopy multispectral transmittance is derived from relative measurements between above- and below-canopy sensors. Based on these measurements, photosynthetically active radiation (PAR) and canopy transmittance are estimated. fAPAR is derived using a two-flux approach based on incident and transmitted radiation. LAI is retrieved either assuming a Beer–Lambert extinction law or, alternatively, by using hemispherical photography to calibrate LAI–fAPAR relationships