Using acoustic Doppler current profilers to assess waves in shallower waters
The Signature1000s have also been attached to moorings to assess waves in shallower waters. In the Chukchi Sea, Thomson and Dr Lucia Hošeková captured a four-day-long wave event near the Alaskan coast, allowing them to explore how sea ice dampens the wave’s energy.
The drifters are, as Thomson puts it, “a totally different animal.” Built by Thomson and his team, the drifters – called SWIFTs (Surface Wave Instrument Float with Tracking) – are designed to operate in harsh conditions. “The SWIFTs are free-floating at the surface, and they just drift, so they’re sort of simple in that regard,” says Thomson. “That puts us in a really neat reference frame. If there’s ice around, we’re moving around the ice, or if it’s just the water, we’re moving with the water. That has some advantages for how we do the analysis because you stay with the same piece of material, whether it’s ice or water, for a while, so you can see how it transforms.”
Along with his former PhD student Dr Samuel Kastner, Thomson previously launched a SWIFT down a river and into a surf zone to assess how breaking waves in the surf zone may enhance mixing between the relative freshwater of the estuary and the saltwater of the ocean. While the ADCPs on the SWIFT measured near‐surface turbulence and velocity profiles, Acoustic Wave and Current Profilers (AWACs) mounted in the outer edge of the surf zone captured wave conditions.
Previous versions of the SWIFT were equipped with a downward-facing Aquadopp Profiler 2 MHz, but are now fitted with a Nortek Signature1000 profiler with an integrated Attitude and Heading Reference System (AHRS) which samples at the same rate as the Signature1000 acoustic measurements (up to 16 Hz), making it even more adept at measuring turbulence and currents when subject to high-frequency motion.