The frequency and distribution of dew occurrence across and within diverse canopies remain unclear, as well as its influence on carbon, energy, and water fluxes across different climatic and canopy conditions. Using data from the NEON network, we aim to examine what is the spatiotemporal variations in dew formations across different climatic regions and canopy types, how dew impacts vegetation function across this climate-ecosystem space, and develop a macrosystem framework on carbon, energy, and water dynamics across a water-availability continuum.
Microwaves are highly sensitive to water because of its large dipole moment. By quantifying the attenuation of a microwave signal going through a dew-wetted canopy, we will be able to provide high frequency, whole canopy information on dew occurrence. We will deploy a GNSS-receiver setup consisting of two choke-ring antennas (VC Choke Ring B3/E6, Septentrio Inc., Leuven, Belgium) coupled to GNSS receivers (PolaRx5, Septentrio, Leuven, Belgium). One of the identical antennas will be placed directly under vegetation, the other in full view of the sky at the top of the NEON tower. As dew deposits on leaves, the strength of the GNSS signal received by the lower antenna will decrease as dew water increases the attenuation of the signal through the canopy, while the high antenna provides a reference point for the unattenuated signal strength of the given satellite passing overhead. Similar setups have been deployed and used for leaf water content monitoring and noted dew events in the signal, but this will be the first deployment targeting dew water quantification. We will deploy the experimental setup at two of our study sites: HARV and UKFS, chosen to represent the two endmembers of our energy- to water-limited continuum. To translate attenuation into water volume, the attenuation will be calibrated against in-situ measurements of water deposition from leaf wetness sensors since the measurement is highly dependent on canopy structure. After this phase, the GNSS attenuation will provide a third source of dew deposition information uniquely integrated to the whole canopy and independent of leaf surface properties. The PolaRx5 receiver is identified as one of the best on the market because of its real-time output, and its low power consumption, a must for field deployment. In addition, the receiver can track GNSS satellites from all five existing constellations, including GPS, Galileo, and GLONASS, therefore increasing the frequency of overpasses, with multiple dozens of GNSS satellites expected to be always available. The high antenna will be placed above the top of the structure to avoid interferences with the metallic structure of the NEON towers.