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Scientists usually map the seafloor first with ship-mounted sonar, then send underwater robots to inspect selected features more closely. The sonar builds a broad picture of depth and terrain; remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) add images, measurements, and—when equipped—samples. Combining those sources helps researchers locate habitats and study marine life, but a terrain map by itself cannot identify every animal living there.
How do underwater robots map the ocean floor?
Start with a broad sonar survey
A research ship can use a multibeam echo-sounder to measure water depth across a wide swath beneath it. The resulting bathymetry shows the shape of the seafloor, including features such as seamounts, slopes, and plains. NOAA describes calibration and testing as part of ensuring mapping data quality; its sonar overview explains how sonar supports ocean exploration.
“Mapping the seafloor” generally means measuring bathymetry and related acoustic data, not photographing or identifying all organisms in an area. Other sonar systems can support different tasks: split-beam sonar, for example, is used for water-column work, while other systems can investigate subsurface structure.
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Use the map to choose places to investigate
Bathymetry gives the expedition a terrain framework for choosing dive targets. Teams can use mapped features and existing knowledge to decide where a closer look may be useful, such as a seamount, deep-sea coral habitat, or abyssal plain. Mapping and close-up exploration are complementary: a map helps direct the next survey, and observations from that survey add biological and environmental context.
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What is the difference between an ROV and an AUV?
The main distinction is how each vehicle is operated. An ROV is remotely piloted by a team, while an AUV carries out an autonomous or programmed mission. Both can contribute to seafloor surveys, but their suitability depends on the mission, configuration, sensors, and ship support available.
| System | How it operates | Typical role in this workflow | Important qualification |
|---|---|---|---|
| Ship-mounted multibeam sonar | Measures depth acoustically from a research ship across a swath. | Creates broad bathymetric coverage to reveal terrain and help select targets. | Bathymetry describes terrain; it does not, by itself, identify all marine life. |
| ROV | Remotely operated by a team, commonly from a ship. | Directed visual inspection of a selected feature; may collect samples if equipped. | Payloads vary by vehicle and mission. Not every ROV has sampling equipment. |
| AUV | Runs an autonomous or programmed survey mission. | Survey or imaging coverage without continuous piloting from the ship. | Coverage, image detail, depth, endurance, and sensors depend on the vehicle and mission. |
ROVs: directed inspection
An ROV lets a team guide a vehicle toward a feature and observe it closely. Depending on its payload, an ROV may carry cameras and lights, sonar, environmental sensors, or tools for collecting biological or geological samples. These capabilities are mission-dependent, not standard on every vehicle. NOAA’s submersibles overview distinguishes remotely operated vehicles from autonomous and human-occupied submersibles.
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AUVs: autonomous survey or imaging
An AUV can follow a planned survey or imaging route without continuous piloting from the ship. Its usefulness depends on the route, sensors, operating limits, and recovery plan. NOAA educational material describes AUV Sirius imagery used to create three-dimensional maps of geography and corals; the Sirius overview gives that example.
These systems are not mutually exclusive. A ship’s sonar can map a broad region, an AUV can image or survey selected areas, and an ROV can be sent to inspect a particular feature or collect a sample. There is no universal performance ranking: the right choice depends on whether the priority is broad coverage, close-up direction, imaging, intervention, or sample collection.
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How do scientists use robot observations to find and study marine life?
After mapping helps identify a target, researchers interpret evidence from the close-up survey. Video and still images can show visible animals and habitat. Sensors can record environmental conditions, and acoustic or imaging systems can characterize terrain. Physical biological or geological specimens and water samples—including environmental DNA samples in some projects—can support further analysis when collected.
- Images and video: document organisms that are visible in the surveyed area and show their surrounding habitat.
- Sensors: measure environmental conditions, depending on which instruments the vehicle carries.
- Physical samples: allow biological or geological material to be examined after collection, if the vehicle and mission support sampling.
- Water samples: can be analyzed for evidence such as environmental DNA in projects that use that method.
Researchers should describe what the evidence establishes. An animal identified in an image is a visual identification, not automatically a specimen-confirmed record. A terrain feature can suggest habitat context, but it does not establish which species live there without biological observations or other evidence.
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What do real expeditions show?
Seascape Alaska 5 combined mapping, ROV dives, and samples
During its 23-day Gulf of Alaska expedition from August 23 to September 14, 2023, NOAA Ocean Exploration reports that Seascape Alaska 5 mapped 28,287 square kilometers, completed 19 successful ROV dives, and conducted dives at depths from 253 to 4,262 meters. The expedition also collected biological and geological samples. These figures describe that specific expedition, not a global average. See NOAA’s Seascape Alaska 5 expedition account.
American Samoa paired ship sonar and ROV exploration
NOAA’s 2026 American Samoa ROV + Mapping Exploration was scheduled for August 20 to September 17, 2026. Its mission description pairs ship-mounted multibeam sonar mapping with ROV operations at approximately 2,000–6,000 meters, targeting areas and features including abyssal plains, seamounts, deep-sea corals and sponges, fish habitats, and the water column. NOAA says mapping data help plan ROV dive targets and support baseline understanding for future exploration and management. The mission dates have concluded, but the cited mission description establishes its plans and goals rather than final outcomes. See the American Samoa expedition page.
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Long-range AUV images can support fisheries research
NOAA Fisheries describes animals—including sea scallops, fish, crabs, snake eels, squid, and skates—identified in seafloor images taken by long-range AUVs. The example shows how remote visual surveys can contribute to fisheries research, including in areas where offshore development can limit access for traditional research vessels. Identification from images should not be confused with confirming each animal from a collected specimen. Read NOAA Fisheries’ account of the long-range AUV.
Why use several systems instead of one?
Each system answers a different kind of question. Ship sonar helps reveal where the terrain changes across a broad area. An AUV can carry out autonomous coverage or imaging, while an ROV gives a team the ability to direct a close inspection and, if equipped, collect material. Combining them lets scientists move from regional context to targeted observations without treating any single map or image as a complete inventory of life.
Which vehicle is appropriate depends on mission design: the desired area coverage and image detail, available sensor payload, whether the team needs to intervene or collect samples, and operating depth, endurance, ship support, and recovery requirements. The cited examples illustrate different roles; they do not establish a controlled head-to-head performance comparison.
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