4.5: Autonomous Underwater Vehicles

If ROVs had besties, they would be autonomous underwater vehicles, better known as AUVs, untethered craft that operate independently on pre-programmed missions. In fact, the US Navy lumps ROVs and AUVs into a single category: uncrewed underwater vehicles (UUVs). AUVs represent the ultimate expression of a robotic deep-sea explorer. Free of any cables, commanded by a computer brain, and potentially able to wander the ocean for unlimited periods of time, AUVs travel in a way that ROVs cannot. Most fly through the water column. Some crawl along the seafloor. Most impressive is their ability to maintain level flight and react to circumstances with limited decision-making capabilities.

Though robotic solo flights present a number of technological and engineering challenges, AUVs have begun to make their mark on 21st-century oceanographic research (e.g., Searle et al. 2018; Meyer et al. 2019). In a 2015 study off Guadalupe Island on the west coast of Baja California, researchers used AUVs to track the behavior of great white sharks (Carcharodon carcharias). Though the sharks regularly attacked the AUVs (they apparently don’t like being followed by a yellow torpedo), the work yielded new insights into the behavior of these magnificent animals (Kukulya et al. 2016).

Researchers have also begun to use AUVs with adaptive tracking systems. In essence, the AUV detects and automatically tracks specific features, such as a particular temperature of water or concentration of plankton. Researchers working off Hawaii in 2018 employed two long-range AUVs to automatically track and sample an ocean eddy—a self-sustaining rotating loop of water tens to hundreds of miles wide. Eddies can generate conditions ideal for the growth of phytoplankton—microscopic plant drifters—which concentrate in a layer known as the deep chlorophyll maximum. By programming the AUVs to track the chlorophyll maximum, researchers were able to observe this subsurface feature in unprecedented detail. To an oceanographer, that’s impressive (Zhang et al. 2019; Zhang et al. 2021).

The latest generation of AUVs promises to greatly expand their capabilities. Hovering AUVs maintain their position over a phenomenon of interest such as a hydrothermal vent. Stealth AUVs rest on the seafloor listening for military targets. New, silicone-based soft robots—so-called bionic AUVs—mimic animals to blend in and observe organisms less intrusively. Uncrewed surface vessels (USVs) allow scientists (and the military) to make observations in remote locations (Braginsky et al. 2020). A catamaran-style USV can even tow a plankton net for sampling microplastics, plankton, and other floating particles (Bazilchuk 2022). For young ocean scientists and engineers, AUVs represent an emerging opportunity to push the boundaries of ocean exploration, a chance to go where no oceanographer has gone before (e.g., Katzschmann et al. 2018; Li et al. 2021; Mazzolai et al. 2022).