Exploring the Air Where Ocean Meets Atmosphere

Imagine standing on a beach, breathing in the fresh, salty air. Have you ever wondered what makes coastal air feel so special? The answer lies in marine aerosols—tiny particles from the ocean that influence sunlight and clouds, playing an important role in shaping our climate.

As part of my PhD research at Southern Cross University, I recently conducted a field trip to Heron Island. This research is part of the Cooling and Shading initiative in the Reef Restoration and Adaptation Program, which is funded by the Australian Government’s Reef Trust and the Great Barrier Reef Foundation, and led by Associate Professor Daniel Harrison of Southern Cross University

The Reef Restoration and Adaptation Program is a partnership focused on helping the Great Barrier Reef resist, adapt, and recover from the impacts of climate change. These efforts aim to protect the reef and buy time while we work as a global community to reduce CO₂ emissions.

Heron Island is located in the southern Great Barrier Reef, about 80 km off Australia’s east coast (Figure 1). We respectfully acknowledge the Gooreng Gooreng, Gurang, Bailai, and Taribelang Bunda peoples as the Traditional Custodians of this Sea Country.

Discovering the Secrets of Coastal Air Using Drones

Marine aerosols form when the wind creates whitecaps on breaking waves, tearing tiny droplets from the wave crests (Andreae et al., 1985; Lewis & Schwartz, 2004). These aerosols are carried into the atmosphere by wind, which determines their movement both vertically and horizontally (Goroch et al., 1980; Lewis & Schwartz, 2004). Other factors like temperature, and humidity near the ocean surface also play a key role in how these aerosols behave.

However, studying marine aerosols in the critical first 100 m above the ocean surface has been challenging. Land and ship-based instruments can’t reach high enough, while planes fly too high to capture the details. That’s where drones come in.

Multirotor drones offer a game-changing solution. These drones are flexible, mobile, and able to hover precisely at different altitudes. They’re also emission-free, making them ideal for research in remote and environmentally sensitive areas (Burgués & Marco, 2020).

How We Used a Drone to Study Marine Aerosols

Our research used the Matrice 600 drone as a platform to carry specialized instruments. Underneath the drone, we attached a box containing a miniaturized Optical Particle Counter (mOPC) and a battery to power the equipment. The mOPC is capable of measuring aerosol sizes ranging from 160 nanometers to 3,000 nanometers.

To measure wind speed and direction, we integrated a TriSonica™ Mini 3D Ultrasonic Wind Sensor approximately 50 cm above the drone mounted to a carbon fibre tube. Placing it above the drone helped reduce interference from the drone's propellers. This sensor was connected to a Beaglebone Black development platform housed in a custom-designed, 3D-printed casing (Figure 2).

Our Fieldwork on Heron Island

We completed about 80 successful sampling flights across four different locations: open water, the reef crest, the lagoon, and close to the island at either low or high tide. Each flight followed a precise strategy to ensure accurate data collection.

• Hovering for Accuracy: Each flight began with the drone facing true north, hovering for 15 sec at 5-metre above its starting point. This step minimized the need for adjustments in wind speed and direction measurements caused by drone movements.
• Ascending in Steps: After the initial hover, the drone ascended vertically in 5-metre intervals, hovering for 15 sec at each level until it reached a final altitude of 105-metres.

This systematic approach allowed us to gather consistent data on aerosols and wind conditions at various altitudes (Figure 3).

What Happens Next?

Now that we’ve returned from Heron Island, the next step is to analyze the data. We’ll investigate how aerosol size distributions vary and how meteorological conditions influence their behavior.

One exciting part of this research is comparing the real-world measurements with computer models of marine aerosol entrainment. By doing so, we hope to improve our understanding of how these tiny particles affect climate processes like solar radiation and cloud formation.