Showcasing Undersea Heroes: Autonomous Underwater Vehicles

EarthzineAutonomous Underwater Vehicles 2017, Original, Themed Articles

Guest Editor Yanwu Zhang kicks off our third quarter theme with a sneak peek at what lies ahead in future autonomous underwater vehicle designs.

Yanwu Zhang’s children imagine next-generation AUVs. Image Credit: Lucy Zhang (left) and Daniel Zhang (right)

On my office wall are my daughter and son’s drawings of next-generation autonomous underwater vehicles (AUVs), merrily colorful and with rows of small windows like on an airliner. They love the cool subs. One question they often ask me is, “What else can an AUV do?”

IEEE Earthzine’s 2017 third quarterly theme addresses exactly that question. Over decades of development, AUVs’ sensing ability, flight range, and on-board intelligence are steadily growing. As a result, AUVs are more often playing a unique role in a wide variety of maritime applications, including ecological studies, marine geophysical and geological surveys, and offshore oil and gas facilities inspections.

As one example, in my home institution, the Monterey Bay Aquarium Research Institute (MBARI), one Dorado-class AUV is equipped with 20 1.5-liter fast water samplers (called “gulpers”). Within a phytoplankton patch, a high biomass concentration leads to a high level of chlorophyll fluorescence. For investigating the peak biomass, it is a critical task to grab water samples at fluorescence peaks. Traditional methods cannot do an accurate job.

Figure 1. The MBARI Dorado gulper AUV autonomously triggered water samplings in a near-surface phytoplankton layer (orange). Per-cell toxin (domoic acid) level in the water samples (represented by the size of asterisks) was the highest where resuspended sediment (purple) extended up to the phytoplankton layer. (From Ryan et al., “Boundary influences on HAB phytoplankton ecology in a stratification-enhanced upwelling shadow,” Deep Sea Research II, Vol. 101, pp. 63-79, 2014. Image Credit: Elsevier)

That’s where AUVs come into play. We designed a peak-capture algorithm to enable the Dorado AUV to autonomously detect fluorescence peaks in phytoplankton patches and trigger the gulpers right on the peaks.

In one harmful algal bloom (HAB) study in Monterey Bay in October 2010, the Dorado gulper AUV triggered water samplings in a near-surface phytoplankton layer, as shown in Figure 1. Water sample analysis showed that the toxin level was the highest where resuspended sediment extended up to the near-surface chlorophyll patch, a finding that supports the theory that enhanced concentrations of trace metals in the sediment promoted domoic acid production in diatoms. This observation is helpful for understanding regulation of HAB toxicity in a complex coastal environment.

This theme will showcase diverse aspects of AUV development and applications. For instance, biomimetic AUVs smartly borrow natural designs in marine animals to overcome some limitations of standard vehicles. A deep rated AUV developed by a team of university students is ready to map the seafloor and sniff out a pre-determined chemical signal and locate its source on the seafloor. To cultivate the next generation of AUV engineers, a newly formed Autonomous Marine Vehicles Competition Committee spearheads an international effort to unify and streamline marine robotics competitions around the globe.

Twenty years ago, when I was a student in James Bellingham’s AUV Lab at the Massachusetts Institute of Technology, the yellow underwater robots were called Odyssey, named after the epic poem in which the hero Odysseus undertook a long journey. Today, AUVs are flying on their long journeys to explore endless wonders in the undersea world. We on shore work hard to make our underwater heroes better-equipped and more intelligent, so that they can fly deeper, farther, safer and accomplish more.

Yanwu Zhang is a senior research specialist at Monterey Bay Aquarium Institute (MBARI). He works on developing targeted sampling methods for autonomous underwater vehicles (AUVs) and other mobile platforms, and applying them in marine ecosystem studies.