I Didn't Know That!: Seafloor Mapping

Ever draw a treasure map as a kid, with an “X” to mark the spot? Turns out, the National Park Service (NPS) makes treasure maps too! But instead of long-lost gold, they’re charting underwater shipwrecks, habitats, and geology.

Did you know?

NPS specialists use sound to “see” beneath the ocean’s surface!  

A robotic uncrewed surface vessel (USV) with a multibeam sonar system collects data while being towed from a larger vessel at War in the Pacific National Historical Park, Guam. Some of the scientists call this USV "Lemmy" for its yellow color like a lemon!

NPS

What is seafloor mapping?

The NPS creates maps to understand, protect, and manage natural and cultural treasures across the parks. But what happens when those resources are underwater?

Mapping underwater is trickier than drawing a map on land. To “see” beneath the water’s surface, NPS specialists use sound. A tool called a multibeam sonar system sends out sound waves that bounce off the seafloor and return to the device. By measuring how long the sound takes to come back, scientists can calculate the depth of the water and create detailed 3D pictures of the underwater landscape that shows the seafloor’s structure and shape. This type of data is called bathymetry. Mapping underwater with a multibeam sonar system is one type of seafloor mapping, also called benthic mapping.

These maps can reveal:

• Natural features like eelgrass beds, coral reefs, and rocky ledges

• Cultural artifacts such as shipwrecks and remains of other human-made objects

• Human impacts including dock pilings and debris

Watch this!

Watch this video to visualize how NPS specialists used a multibeam sonar system to collect seafloor data in the field. The star of the video and many NPS seafloor mapping adventures is named Lemmy! Lemmy is a yellow uncrewed surface vessel (USV) that carries a multibeam sonar system. 

Why does it matter?

Seafloor maps are more than just cool visuals. They help answer big questions across many scientific fields including:

• Oceanography

• Hydrology

• Geology

• Ecology

• Biology

• Engineering

• Archaeology

• Anthropology

Park managers use them to support real-world park needs like:

• Tracking habitat change and informing restoration potential

• Understanding coastal erosion, sediment transport, glacial retreat, and landslides

• Investigating long-term ecosystem change

• Guiding management and safety decisions

Seafloor mapping in action!

Here are a few ways NPS specialists have put Lemmy and its sonar to work:

Lemmy mapping the coral reef offshore of the Asan Beach Unit at War in the Pacific National Historical Park. The left photo shows the spur and groove coral structure from the water’s surface as it is being mapped, and right image shows the same structure captured in the multibeam sonar data.

NPS

• War in the Pacific National Historical Park, Guam – Mapping to document World War II artifacts that still remain on the seafloor and the natural environment (including coral reef), and to explore how history shaped the island as it is today.

Lemmy collecting multibeam sonar data along the Lake Clark National Park and Preserve coastline.

NPS

• Lake Clark National Park and Preserve, AK – Mapping to determine water depth and seafloor structure and to support resource management decisions related to development.

Multibeam sonar data showing seagrass (orange and yellow) offshore of Duck Harbor in Cape Cod National Seashore.

NPS

• Cape Cod National Seashore, MA – Mapping eelgrass beds to monitor decline and guide restoration.

NPS survey team members bring Lemmy back to shore after an autonomous mapping mission.

NPS

• Fire Island National Seashore, NY – Mapping to document sediment transport and support decisions about shoreline management, while also supporting dredging for safe boating access.

Lemmy collects multibeam sonar data in Pedersen Lagoon at Kenai Fjords National Park (with Pedersen Glacier in the background).

NPS

• Kenai Fjords National Park, AK – Mapping water depths and underwater deposits within Pedersen Lagoon after a landslide triggered a tsunami to model the event and improve safety planning.

Pass it On!

Did you learn something new? Pass it on! There is so much to learn about the natural world and how to explore it, but there's no way for everyone to be an expert in everything. That's why sharing knowledge is so important. Next time you look out over the ocean, remember, there’s a whole hidden world beneath the surface, and the National Park Service is mapping it—no treasure map required!

Download or screenshot this card to share with a friend or help you remember what you learned about seafloor mapping.

Check out other I Didn’t Know That! topics.

Alt Text for Infographic

Did you know that the National Park Service makes treasure maps? But instead of long-lost gold, they’re charting underwater shipwrecks, habitats, and geology.

• Why? Scientists need to document and assess what natural and cultural resources are in parks so they can preserve and protect them!

• How? Scientists can use sound waves to “see” beneath the surface and map the seafloor to identify underwater resources.

• What? During seafloor mapping, scientists collect “bathymetry” data. This provides water depth and reveals the shape and structure (topography) of the seafloor.