During the 2021 hurricane season, the National Oceanic and Atmospheric Administration (NOAA) and dronemaker Saildrone sent an uncrewed surface vehicle (USV) into the midst of Hurricane Sam. It survived the ordeal and emerged with invaluable data to help boost hurricane track forecasting. It was also the first time a USV was directed into a hurricane.
The Saildrone Explorer SD 1045 vessel spent 24 hours inside the hurricane, facing down winds over 90 miles per hour and waves that surpassed 50ft in height—without losing a single sensor. The drone collected data from the Category 4 hurricane’s edge through the eyewall while continuously providing near real-time data, images and video of the storm via satellite.
“If you look at the high-resolution pitch and roll data, SD 1045 was really getting tossed around. It slid broadside down 80-foot waves and it went completely upside down a few times. It’s not high wind speeds that cause a problem for the vehicle; it’s the power of the waves,” said Christian Meinig, director of Engineering Development at NOAA’s Pacific Marine Environmental Laboratory (PMEL).
A saildrone is a wind- and solar-powered USV that can collect data for up to a year on the open ocean. The Saildrone Explorer has a 23-foot hull and a heavy keel to help keep it upright in the water. The drone is powered by a 15-foot rigid wing that functions somewhat like a sail—but with a design that’s similar to an aircraft wing. On a sailboat, the sail is adjusted with ropes and human power, while the saildrone’s wing uses aerodynamic control—the same way that an aircraft’s tail controls its pitch to generate lift. Wind passing over the wing produces thrust, and a small tab on the end of the tail that is attached to the wing controls the angle of attack.
Each saildrone is equipped with GPS and an onboard computer that enables them to navigate a series of waypoints—but the vehicle can autonomously factor in currents and winds along the route. The vehicle is supervised remotely from Saildrone Mission Control in Alameda, Calif.
In terms of payload, each vehicle comes equipped with scientific-grade sensors to measure a variety of key atmospheric and oceanographic environmental variables in real time.
To ensure operational safety, a saildrone carries an Automated Identification System (AIS) transceiver that allows it to monitor nearby commercial traffic. It also has four onboard cameras that track its surroundings. Since the drone is slow relative to other craft and is designed for high visibility, the chance of collision is minimized.
Data from the Saildrone Explorer has already proven to be quite useful—and the mission’s success has opened doors to further exploration of extreme weather events. There have been significant improvements in forecasting a hurricane’s path thanks to satellite data, buoys, and sensors dropped from aircraft; however, predicting hurricane intensity is still a big challenge. To understand how hurricanes grow and intensify, data needs to be collected from inside the hurricane right at the ocean’s surface, where heat and momentum are generated from the exchanges of energy between the ocean and the atmosphere. SD 1045’s mission was to collect data on exactly that phenomenon—and the sturdy drone did so for an entire day.
“The point of the whole scientific mission was to measure the surface flux within hurricanes, especially around the eyewall—and we got it!” said Chidong Zhang, director of the Ocean Climate Research Division at NOAA PMEL. “But before the mission began, my primary goal was to see if the new short-wing vehicle would work, because we just didn’t know. I told everyone, ‘If this vehicle can survive a hurricane, then this would be a big success story.’ The whole mission exceeded my expectations.”
Future missions will feature Saildrone USVs working in coordination with underwater gliders and uncrewed aerial drones to collect data from the upper ocean, ocean-atmosphere interaction and lower atmosphere inside a hurricane. Groups of saildrones will also be deployed in a hurricane to provide a multi-dimensional look inside the hurricane’s eyewall at different quadrants.
That data will in turn help scientists develop more accurate hurricane forecasts—which could give climate and disaster response agencies, as well as coastal communities, the information they need to better prepare for these natural disasters and save lives and property.
Look for more of these tough, resilient drones to sail into the eyes of hurricanes and gather even more hard-to-access data.
Read more about the use of drones to help safeguard human lives at Study Explores Using Swarm of Tiny Drones to Transform Search-and-Rescue Operations.