The California Heartbeat Initiative is revolutionizing how to monitor the water available to an ecosystem. Plants must have water in their tissues to convert sunlight into food, produce oxygen, and stay upright rather than droop. The gold standard for evaluating a plant’s water status is to sample its leaves both before dawn and in midday heat. Unfortunately, this method is laborious and time consuming. It is difficult to measure more than a few plants at a time, much less an entire landscape.

From soil to outer space

CHI is working to automate this process. The project conducts drone flights to gauge water content in the atmosphere, in plants, and in soils across the landscape. Additional measurements of surface water and groundwater resources are also being taken. The project correlates trusted local monitoring methods with remotely sensed data from drones and satellites. The project will integrate all of these data to establish new methods to monitor hydrologic status at landscape scale. All of these environmental measurements can be accessed via an online portal that delivers the information easily for analysis.

A compact sensor package

CHI has combined the detection of environmental conditions into one compact instrument bundle. Mounted atop a tripod that can flex with the wind, the CHI sensor package bristles with a suite of research grade sensors capable of monitoring a wide range of environmental characteristics.

Crowning the tripod is a miniaturized climate station. Able to measure the usual weather characteristics, from humidity to rainfall and temperature to wind speed, it can also measure the availability of light wavelengths capable of powering plants, thanks to a photosynthetically available radiation (PAR) sensor. A radio listens for electrical bursts of a specific frequency to count lightning strikes. And a pair of leaf-shaped sensors hanging off the side measures the degree of wetness nearby leaves are experiencing.

Cables from the tripod power instruments on a nearby tree and beneath the ground. The instrument lashed to the tree is a sap flow meter. It measures how fast fluid is moving from the tree’s roots toward its leaves. Leaves need water to make sugar through photosynthesis, then transpire that water into the atmosphere. The sap flow meter pulses heat into the fluid within a tree’s vessels, and measures how long it takes for the warmed sap to rise to a nearby heat sensor.

Soil and tree canopy connections

Beneath the surface, the cables fuel instruments that measure soil moisture at range of different depths. These readings give a sense of how much water is available for plant roots to absorb.

A data logger clipped to a leg of the tripod stores the information gleaned from all of the instruments. Finally, an adjacent transmitter sends the data wirelessly to reserve headquarters. From there, it is uploaded to the internet and available to researchers in real time.

The solar panel that powers all of the instruments allows the sensor package can be deployed far from the grid.

View from the sky

CHI deploys unmanned aerial vehicles, or drones, to collect data across a large area. Multi-spectral and 360° cameras mounted on the drones collect information on topography and surface water distribution as well as rates of photosynthesis.  

The resulting data can be used to reconstruct 3D models of entire trees, and track the fate of environmental water.