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TORNADO CHASER HEADS OFFSHORE TO RECORD STORM SURGES
Acoustic Doppler Profilers Offer High-Resolution Data
San Diego, USA -- Filmmaker and renowned tornado chaser Sean Casey is looking out to sea for his next exploration of na-ture’s power—hurricanes and the storm surges they create.
Casey is putting the finishing touches on a specially reinforced 29-foot boat that will carry him, a researcher, a captain and a crewmate to the leading edge of hurricanes for a close-up look at the ferocity of these devastating storms. As the storm approaches landfall, Casey and his crew will place high-tech instruments that provide details on the height, velocity, and wave energy delivered by the surge of water stirred up by hurricanes in the Caribbean and Gulf of Mexico. They’ll also be filming powerful storms for National Geographic.
“We’ll be filming whatever we see above the water’s surface,” Casey says. “We might have this boat, if the conditions are right, ride out the storm inland. At the very base, this boat will be a special delivery system.”
The Big, Big Screen Casey blew into the public eye with his jaw-dropping filmmaking and deep knowledge of storm systems on the Discovery Chan-nel’s Storm Chasers in 2007, and followed up his small-screen work with the 2011 release of full-length IMAX feature Tornado Al-ley. Tornado Alley was funded in part by a grant from the National Science Foundation. During the production of Tornado Alley, Casey designed the TIV 2, his second Tornado Intercept Vehicle. The heavily armored van acted as a shooting platform and data gathering base, and
allowed Casey to position portable meteoro-logical instruments in the paths of oncoming twisters. It also served as inspiration for the hur-ricane project. Casey’s new boat, the SSV, or Storm Surge Ves-sel, is 29 feet (8.8 meters) long and 8.5 feet (2.6 meters) at the beam. Its cabin is formed of a single piece of 1/8-inch aluminum for durabil-ity and water-tightness, and its windows are formed of half-inch polycarbonate, yielding
Sean C. Casey is an American IMAX filmmaker and storm chaser who appeared in the Discovery Channel reality television series Storm Chasers. Casey created an IMAX film called Tornado Alley about chasing tornadoes and had to build the Tornado Intercept Vehicle (TIV) and the Tornado Intercept Vehicle 2 (TIV2) to film inside a tornado.
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a total displacement of 9,000 pounds (4,000 kg). A pair of HJ241 Hamilton jets mounted to twin Chevy V-8 small block marine engines will propel the craft in as little as 8 inches (20 cm) of water. “It’s a ruggedized boat, so when things do get bad, it will be very difficult to sink,” says Casey. Casey says early designs included a filming turret and even amphibious capabilities, but he decided simplicity and re-ducing extra weight was more important than extra features. “When you’re playing with a hurricane, you want all of your seaworthy attributes,” he points out.
“We definitely want to be smart about it,” Casey says. “What-ever we do, chasing tornadoes or whatever, we’ve always had a good idea of how to get out of a bad situation. The whole idea of being in a storm surge is daunting. We have a mission prior to the hurricane making landfall, then finding a viable place to ride out the surge. The idea is that we hang out on the coast as long as we can because we want to film that and take data from the environment, as long as we have a way out.”
Casey explains that as the storm approaches the beach, he and his team will deploy wave measurement instruments, film the oncoming hurricane, then work their way inland, past the 10-mile point at which most of the surge energy is expended. Acoustic Doppler Profiling: A Slice of the Action
Since Hurricane Rita blew through the Gulf of Mexico in 2005, scientists have used depth sensors to record the magnitude of storm surges. Those early readings were taken with pressure sensors, or strain gauges. Researchers are also tapping into a steady stream of sea surface data from satellite-mounted radar altimeters.
Casey is equipping his team with acoustic Doppler profiling systems, or ADPs, from SonTek, which capture much more detailed information not just on the height of the surge, but on the direction and speed of the water throughout the surge’s profile.
That is especially important in studying storm surges, notes SonTek product manager Janice Landsfeld at the company’s headquarters in San Diego, California.
Storm surges are more than just a big wave, Landsfeld ex-plains. A cell of low atmospheric pressure inside a hurricane can draw water upwards, raising the local sea level, and energy
Example of the RiverSurveyor M9 being used during a flood event in North Dakota, USA.
Sample high-definition data from the RiverSurveyor M9.
from the storm pushes the surge towards land. Mas-sive forces bend and redirect the moving water as it travels. On top of the surge, waves can form, adding destructive power to the hurtling water. The mass of water is not moving at a uniform speed, though—complex variables including friction and density can create zones of faster or slower moving water, as well as turbulence.
For instance, a deep approach to land can absorb surge energy below the surface, blunting the blow of landfall. But if the sea floor slopes gently to land as it does on Florida’s Gulf shores, surges are more likely to push deeper inland. If the surge pushes into a narrow bay or inlet—like Hurricane Isabel did in 2003 in the Chesapeake Bay, or Hurricane Sandy pushed into New York Harbor in 2012—it can be greatly amplified. Variables such as rainfall, river flow and tides can also impact the devastation storm surges can cause. From beneath the surge, ADPs can provide a wealth of data on the incoming forces.
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Alexandru Sheremet, a University of Florida researcher who is serving as Casey’s technical advisor, will use the surge data to correspond to studies of storm impacts on buildings, and to validate surge models.
He recommended taking aboard a SonTek Argonaut-XR ADP, an acoustic Doppler profiler capable of collect-ing and storing more than 20,000 data samples with 10 acoustic velocity cells and a dynamic AutoTide feature that automatically adjusts the size of the velocity measure-ment cell based on fluctuations in water depth. He also suggested Casey take on a SonTek RiverSurveyor M9, a multifrequency ADP mounted on a floating hydroboard.
Towed across the water’s surface, the RiverSurveyor profiles direction and speed with a ping rate of up to 70 impulses per minute, switching acoustic frequencies automatically for seamless data collection in fast-changing conditions. The systems will provide information on the level, or height, of the surge and waves. They also deliver a view of what’s happening at every level of the surge, much like a CAT scan provides a detailed view of an entire slice of a brain or heart. “When we deploy instruments in a storm surge, we want to gather data on how fast the flow is, what is the verti-cal structure, what kind of waves we have on top of the storm surge,” Sheremet says. “Acoustics is the technology that allowed us to use the relatively cheap, very efficient instruments to measure current velocity. They allow you to gather data remotely and measure velocity at many levels. You get an entire profile. “What was there previously was really clunky,” he adds. “Current meters had all sorts of issues. The acoustic ver-sion of them is way better. It’s worlds apart.”
Waiting for the Big One Casey says his goal is to deploy the Argonaut-XR and the RiverSurveyor M9 in areas not already served by other surge monitoring projects. “There are a lot of underserved islands off the U.S. coast that don’t get outfitted with instruments,” he says. “My goal is primarily to take instruments to places they haven’t been able to reach—remote beaches, swampland, barrier islands.”
Kevin Labbe, the SonTek application specialist training
Casey on operating the ADPs, points out that gathering acoustic data in the water will provide greater detail and greater accuracy than standard surge detection instruments.
“Our sensor can sit out in the air before a storm surge comes in and have the storm surge pass over it, dry out, and save the data for collection,” he explains. “As long as the instrument doesn’t move, you’re going to get a very accurate reading. With a pressure sensor—an alternative method—you’re going to get drift. The ADP is also simple to operate. And unlike an instrument deployed on a building, bridge or satellite, you don’t just get level, you know how fast it’s moving—you get a measurement of force.”
Casey is battening down the hatches in hopes of storms to chase this hurricane season, and he’s contemplating the challenges of capturing their power on camera after more than a decade of filming tornadoes.
“Tornadoes are such a visual thing: there’s such singularity to them,” he says. “With a hurricane, you’re just immersed in that weather for hours
From the SSV, Sean Casey will be filming hurricanes in 5K video, dazzling high-resolution images. Similarly, the profiles he gets in the water will deliver an extremely high-res look at the energy in storm surges. Casey’s wave data will be collected with
acoustic Doppler profilers, or ADPs, which use highly targeted acoustic signals to measure the level (or depth), speed and direction of water. Casey is deploying two ADPs from SonTek—a bottom-mounted Argonaut-XR and a floating RiverSurveyor
M9. Both emit acoustic signals in highly focused beams, analyzing the reflected sound from multiple “cells” at different levels in the water. As the surge passes, the instruments are intelligent enough to recognize changing conditions in real-time and adjust their operation in different ways. This kind of intelligent adaptation is crucial in the midst of rapidly-changing, high-intensity storm events. Data collected by the Argonaut-XR and RiverSurveyor M9 can provide a detailed picture of advancing storm surges and the waves traveling with them, offering scientists a close-up look at one of nature’s most powerful forces.
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and hours, just tossed around. This is going to feel like being inside a tornado for hours and hours and hours, with sustained winds of 120, 130, 140 miles per hour. That can be quite a little voyage.”
Labbe says data from the Argonaut-XR and RiverSur-veyor will bring the rest of us on a voyage of discovery into the complex world of storm surges.
“The fact that National Geographic is going to be in-volved in this is pretty exciting, and that it’s going to be in the public eye,” he says.
Watch ABC 10News story featuring Sean Casey’s up-coming IMAX 3D project “Extreme Weather 3D” here.
SonTek Application Specialist, Kevin Labbe, takes a moment to pose with Casey’s reinforced “extreme weather” tow vehicle.
