By Craig Anderson

Hovering autonomous vehicles (HAUVs) are set to revolutionize underwater exploration and data collection. These vehicles differ from traditional AUVs in that they can maneuver precisely in any direction. Some vehicles offer true 6 degrees of freedom (DOF) operation, enabling them to fully image the complex features of reefs, from imaging directly downward to capture benthic habitats to imaging more horizontally for imaging fish.

Other HAUVs, such as ARV-i by Boxfish Robotics, can remain underwater for long periods, docking in a charging bay and transferring data before going out again. These underwater resident HAUVs allow for detailed data collection throughout large areas over time or frequent monitoring of sensitive sites. Power can be supplied by several means, including cable and solar buoys, and data can be transmitted wirelessly or over fiber or copper cable.

Mission Planning

When choosing mission planning software, one must consider carefully whether to work with cloud software or computer-based apps. In the field, internet access can be slow, unreliable and not always available. Computer-based apps, such as Boxfish Robotics’ SafePath mission planner, have an advantage when working in more remote locations, on smaller vessels, enabling missions to take place with fewer dependencies. Mission planning software generally makes it easy to set up survey patterns (mowing the lawn) and may allow specification of image overlap.

Once the vehicle is put into the water, ideally, it starts automatically, and progress can be monitored through acoustic communications, such as with the Boxfish AUV. The current waypoint and the distance to that waypoint are shown and updated frequently on the SafePath software. A variety of commands can be issued over the acoustic link, including to pause or abort the current mission.

Autonomous Operation

HAUVs can use a combination of USBL acoustic positioning and DVL for precise measurement of movement and altitude; INS to measure acceleration, which is used to estimate velocity; and dead reckoning, using thrust and drag estimations. These sensors are typically fused together to get both accurate and precise positioning information.

In addition, USBL systems generally provide an acoustic communications channel to monitor progress and control AUV operations.

Integrated Sensors for Comprehensive Data Collection

To enhance the capabilities of HAUVs, some vehicles can carry a range of sensors, including imaging sonar, CTDs, pH sensors, hydrophones, turbidity sensors and fluorometers. These sensors provide valuable data on water quality, temperature, salinity and other environmental parameters. The integration of these sensors allows for comprehensive data collection, enabling researchers to gain a deeper understanding of underwater ecosystems and their dynamics.

Optional Tethered Operation

Some HAUVs offer optional tethered operation to allow them to function as ROVs. This can assist in hazard identification prior to AUV missions or offer the operator more control when AUV operations are less ideal or not required.

Some HAUVs offer the ability to run autonomous operations while monitoring telemetry and the main camera via tether.

Photogrammetry to Create 3D Reconstructions

HAUVs typically offer 4K video or photo capture or both, which can be used to build 3D reconstructions of the underwater environment. RAW images allow for consistent adjustment of exposure, white balance and contrast in the images. Image capture should allow for shutter speed adjustment, which can prevent motion blur while capturing images. Images can be captured from video but are lower in resolution and white balance, and exposure adjustment is often not possible due to the much lower dynamic range. JPEG images have similar issues.

Lighting is very important, and lighting that is distant from the camera lens and configured to minimize backscatter is important to getting the best data.

The images can be processed using software such as Agisoft Metashape, a powerful photogrammetry software that creates detailed 3D reconstructions from the collected image data. It’s important to have a reference scale. This can be done using laser scalers or stereo cameras.

The precision and quality of the images are important to create accurate, detailed, and reliable 3D reconstructions, which are essential for many applications in environmental monitoring and marine science and are just as applicable to archaeological surveys and infrastructure inspections.

Estimating Fish Species with Video Transects

HAUVs that can be operated horizontally (or at any angle) can be ideal for estimating the abundance of fish species. Wide-angle zoom lenses and dimmable lighting can minimize backscatter reflections for better imaging.

Customizable Boxfish AUV

The Boxfish Robotics AUV is a surface-launched, highly portable system that can be operated by just one person. It supports robust fiber-optic tether solutions for ROV or autonomous operation with video monitoring. Its unique, 6 DOF patented design can operate down to 600-m depth. The Boxfish AUV can carry a wide range of environmental sensors and sonars for data collection. It enables monitoring of autonomous mission progress and the capability to intervene during a mission if needed. In addition, if tether communications are lost during an ROV operation, the vehicle can drive itself to the surface.

ARV-i: Resident Vehicle

Boxfish Robotics and Transmark Subsea have collaborated to create ARV-i, an innovative resident HAUV that can dock underwater. While docked, the ARV-i can wirelessly recharge and send data at Ethernet speeds. The ARV-i supports all of the features of the Boxfish AUV. The system enables completely autonomous operation to be monitored and controlled from a command center anywhere in the world. The ARV-i can be equipped with a range of sensors for comprehensive data collection. It can be deployed to autonomously monitor large areas or to monitor changes in the environment over time.

In 2023 and 2024, Boxfish Robotics collaborated with Mocean Energy in Scotland, installing a dock for Mocean’s subsea battery pack as part of an underwater wave energy project. The ARV-i vehicle showed that it could leave the dock, inspect the installation and surrounding environment, and return to the dock.

The vehicle has also demonstrated its capabilities in Norway, where it was installed in a fish net for extended periods, capturing data on the fish population and parameters of the net.

 

Conclusion

HAUVs’ ability to hover and capture high-resolution images, combined with the ability to integrate advanced sensors and user-friendly mission planning software, make them invaluable tools for researchers and professionals in marine science and environmental monitoring. As we continue to explore the ocean, these innovative vehicles will undoubtedly play a crucial role in advancing our understanding.

Craig Anderson is co-founder and head of R&D at Boxfish Robotics.