Find bathymetric data services
Seafloor mapping is not new. However, the skills mariners use to survey and safely transit treacherous waters have progressed with new technologies. There are also new uses for seafloor maps beyond navigation: the ocean floor is now mapped to lay submarine communication cables, leverage natural resources, construct wind turbines, or define maritime sovereign boundaries.
Today, there are several methods for surveying the seafloor, and many different data formats for bathymetric data. You'll start by exploring data available as map services.
Explore an oceans data portal
The first data portal that you'll explore is the General Bathymetric Chart of the Ocean (GEBCO). GEBCO compiles and shares authoritative and publicly available bathymetry datasets from different sources, including governments and research agencies.
- Visit https://www.gebco.net/ and explore the site.
It's possible to download data from this site, but instead, you'll access it through a Web Map Service (WMS). You can view WMS layers in ArcGIS Pro with a URL, so you'll search this website for the correct URL.
- At the top of the page, point to the Data & Products tab. Click GEBCO Web Services.
- Read the Access GEBCO's Web Services page. Click the services available link.
If the website has changed, or you are unable to find the link, go to https://www.gebco.net/data_and_products/gebco_web_services/web_map_service/.
The GEBCO WMS page appears. The URL at the top of the page is the information that you need to access the WMS data.
- Copy the URL: https://www.gebco.net/data_and_products/gebco_web_services/web_map_service/.
WMS layers allow you to access data without downloading it. The data exists as raster images of maps that you can view and explore in GIS software as a layer. You can reproject WMS layers to match your other map layers, but you can't edit, copy, or use them as inputs in analysis tools. WMS layers are useful as reference data: it is easier to compare other GIS layers to a reference map when that map is itself available as a WMS layer.
The page has more information about the WMS.
- Read through this information to learn if there are any restrictions on its use.
Many datasets are publicly available for some purposes but not all. For example, you may be allowed to use the data for educational purposes but not commercial. You may be allowed to explore the data but not make derivative products from it. You are usually required to acknowledge the data's source.
Question 1: Are you allowed to use this data? How do you know?
Question answers are provided at the end of the lesson.
Question 2: How should you acknowledge the data in your final project?
View a WMS layer in ArcGIS Pro
Next, you'll view the WMS in ArcGIS Pro.
- Start ArcGIS Pro. If prompted, sign in using your licensed ArcGIS account.
If you don't have ArcGIS Pro or an ArcGIS account, you can sign up for an ArcGIS free trial.
- Under Blank Templates, click Map.
- In the Create a New Project window, for Name, type Ocean.
- For Location, click the Browse button and choose a location of your choice, for example, drive C.
- Leave the Create a new folder for this project check box checked.
This folder is where you will store all of the data and documents related to your research project, including the ArcGIS Pro project.
- Click OK.
ArcGIS Pro opens, showing a map of the world. There may be panes open on either side of the map.
- On the ribbon, click the View tab. In the Windows group, click Reset Panes and click Reset Panes for Mapping (Default).
Now the only open panes are the Contents pane and the Catalog pane. You'll use both of these later.
- On the ribbon, click the Map tab. In the Layer group, click the bottom half of the Add Data button and click Data From Path.
The Add Data From Path window appears. You can add different types of map data services this way.
- For Path, paste the URL to the GEBCO WMS: https://www.gebco.net/data_and_products/gebco_web_services/web_map_service/mapserv?
Another menu appears.
- For Service type, choose A WMS OGC Web Service.
OGC stands for Open Geospatial Consortium, which is the international geospatial standards organization that developed the WMS protocol.
- Click Add.
New map data appears.
- In the Contents pane, click the arrow next to the WMS layer to expand it. Expand its sublayer also.
There are seven more sublayers. It is common for WMS layers to contain a collection of related maps as sublayers.
- While pressing the Ctrl key, click one of the sublayer check boxes.
All of the sublayers turn off.
- Turn on the GEBCO Grid colour-shaded for elevation layer.
The layer appears on the map. The colors depict elevation above and below sea level. Darker blues represent deeper ocean depths.
- Turn off GEBCO Grid colour-shaded for elevation and turn on GEBCO Grid shaded relief.
The coloring of this layer is the same, but it is textured with shaded relief, a cartographic technique for mapping terrain. It mimics how the sun would illuminate some hillsides and cast others into shadow. It gives the map a more naturalistic and three-dimensional appearance.
- Pan and zoom to explore the map.
In some areas, the ocean floor is crossed with straight lines that do not appear natural.
- In the Contents pane, turn on GEBCO_LATEST TID 2 Grid.
Intersecting lines appear on the map. Many of these lines correspond to the unnatural-looking straight edges seen in the previous step.
- In the Contents pane, expand the GEBCO_LATEST TID 2 Grid sublayer.
A legend appears.
The lines on the map indicate areas where data has been collected. TID stands for Type Identifier and indicates different data collection methods.
Bathymetric data is available for the entire world, collected by satellite, but only at low resolutions. Higher-resolution data must be collected using hydrographic survey methods, the most common of which is multibeam sonar systems, and it is only available for parts of the ocean. The straight edges you saw crossing the ocean floor are areas where data was collected by multibeam surveys and other methods aside from satellites.
This map demonstrates the fact that much of the ocean remains unmapped at higher resolutions, especially areas far from land.
Read more about bathymetry data collection methods and the extent of seafloor mapping at Seafloor Mapping: The Foundation for Healthy Oceans and a Healthy Planet, made for World Oceans Day by NOAA Ocean Exploration and Research.
Now that you've viewed the data, you can assess whether or not the WMS layer will be useful in your project. The GEBCO Grid shaded relief sublayer uses bright colors and shaded relief that makes the ocean depths in this map easy to interpret. It will be a useful reference layer. The GEBCO_Latest TID 2 Grid sublayer will be useful for assessing and comparing collection methods later when you conduct analyses. It can provide context on where bathymetry data is most accurate, and where it is interpolated.
Explore an ocean basemap
The WMS data you explored is a type of a service. Services are data that is streamed to your map. They are owned, managed, and stored by someone else. Services are regularly updated and don't take up space on your computer. They also allow you to view large amounts of data quickly.
One of the most common types of map services are basemaps, which are intended to provide geographic context for other map data. Esri provides a variety of basemaps that can be accessed directly within ArcGIS software. Your map already has a basemap, but you'll change it to one that is more suited to oceanography.
- In the Contents pane, collapse the GEBCO_Latest TID 2 Grid sublayer. Turn off all of the WMS sublayers.
- On the ribbon, click the Map tab. In the Layer group, click Basemap. In the Basemap gallery, click Oceans.
The map updates.
You can read about the Oceans basemap on its item page.
- Pan and zoom to explore the new map.
- Turn on the GEBCO Grid shaded relief sublayer.
The basemap's labels are still visible. The basemap is made of two layers: World Ocean Base sits under the WMS layer, and World Ocean Reference, containing the labels, sits on top.
- Select the topmost WMS layer. On the ribbon, click the Appearance tab. In the Compare group, click the Swipe tool.
- Swipe on the map to compare the GEBCO layer to the basemap. Explore various areas in the North Atlantic Ocean.
Question 3: What are some similarities and differences between the WMS layer and the basemap?
- On the ribbon, click the Map tab. In the Navigate group, click the Explore tool so you can pan the map instead of swiping.
- In the Contents pane, turn off the WMS layer and collapse it.
Read about how and why the Esri Oceans basemap was created at A Foundation for Ocean GIS.
Much, but not all, of the Oceans basemap is made from the same GEBCO data that appears in the WMS layer. Even though it duplicates data that you already have, it will be a useful tool for your project in two ways: it provides labels for marine features, and its pale colors will make it more useful as a contextual background for any maps you produce.
Explore seafloor geomorphology
You'll add one more map service to your project: a layer that maps geomorphic features of the world's oceans. Geomorphology seeks to understand why landscapes (or in this case, seascapes) are shaped the way they are, and how they change over time. It is the study of topographic (land) and bathymetric (ocean) features. You'll add this layer from ArcGIS Online and explore it in ArcGIS Pro to gain insight into your study area.
- In the Catalog pane, click the Portal tab and click the Living Atlas tab.
This tab filters your search to only content from ArcGIS Living Atlas of the World, a curated collection of authoritative maps and geographic data.
- In the search bar, type World Seafloor Geomorphology and press Enter. In the search results, point to World Seafloor Geomorphology.
Metadata about this item appears in a pop-up window. The Type property is listed as Map Image Layer.
Map image layers are maps shared as image tiles. In this way they are similar to the WMS layer you viewed earlier. The difference is that WMS layers are based on raster data, while map image layers are based on vector data. You'll learn about the difference between vector and raster data later in the lesson.
- In the search results, right-click World Seafloor Geomorphology and click Add To Current Map.
The World Seafloor Geomorphology layer is made available through ArcGIS Living Atlas, but it was published by GRID Arendal, a nonprofit environmental communications group.
The data appears on the map. It is semitransparent, so the basemap shows through. It uses different colors to represent different bathymetric features.
- In the Contents pane, turn off the World Ocean Base layer to see the colors on the map more clearly.
- On the ribbon, click the Map tab. In the Inquiry group, click the Locate button.
The Locate pane appears.
- In the Locate pane, in the search bar, type New England Seamounts and press Enter.
The map zooms to a line of yellow spots arcing across the northern Atlantic.
A seamount is a peak or group of submarine volcanic peaks rising more than 1,000 meters above the seafloor. They are most often conical in shape. Some seamounts near the surface feature coral atoll islands. A seamount that emerged from the ocean to form an island may erode by wave action and resubmerge to become a flat-topped guyot submarine mountain.
- Zoom in further on the New England Seamounts. Close the Locate pane.
- In the Contents pane, expand the World Seafloor Geomorphology layer. Press the Ctrl key and click one of the sublayer arrows to expand all sublayers at once.
You now have a legend that explains all of the colors of the map. However, on the map, the features overlap, and there are many colors, so it's not always easy to read features.
- Press the Ctrl key and click one of the sublayers to turn them all off at once.
- Turn the Seamounts sublayer back on. Scroll to the bottom of the list and turn on the Zone layer.
The seamounts exist in the Abyss zone. To the west of the seamounts is the continental shelf, bordered by the continental slope.
- Turn on other sublayers one at a time to observe them on the map.
- In the Contents pane, right-click World Seafloor Geomorphology and click View Metadata.
The Catalog view appears, showing more information about the layer.
- Read about some of the features visible on your map.
Question 4: What are some other features found in the area of the New England Seamounts? Make an observation about a geographic pattern visible from this data in this area.
- Close the Catalog view.
- Collapse and turn off the World Seafloor Geomorphology layer. Turn on the World Ocean Base layer.
- On the Quick Access Toolbar, click the Save button.
Read about the ocean environment of some of the New England Seamounts at Northeast Canyons and Seamounts Marine National Monument.
The World Seafloor Geomorphology layer will help you better describe, classify, and understand your study area. You'll keep it in your project as a reference layer.
So far in this lesson, you've explored different types of map services: data that is stored elsewhere and accessed via the internet. Next, you'll download data so you can use a local copy stored on your computer.
Download bathymetric data
Downloading data offers some advantages over accessing web services: you are able to edit the data, change how it is displayed, use it to create new datasets, and perform analysis. Additionally, the data is not at risk of changing or disappearing.
Download digital elevation models
You'll find and download two digital elevation models (DEM) from the National Oceanic and Atmospheric Administration (NOAA).
- Visit https://ngdc.noaa.gov/mgg/bathymetry/relief.html.
National Centers for Environmental Information (NCEI) is a branch of NOAA and manages one of the largest archives of environmental data in the world. Included in this collection are many bathymetry data products.
- Explore the links on this page to learn about the various data offerings.
Question 5: What are some of the data formats available?
Geographic data is available in many different formats. Some data formats require processing before they can be used. Next, you'll download some of the data from the NCEI site and add it to your map in ArcGIS Pro.
- Return to the main page and click Search Bathymetric Data by Map.
- If necessary, click Redirect now. Alternatively, go to https://www.ncei.noaa.gov/maps/bathymetry/.
The Bathymetric Data Viewer appears. This tool offers a visual interface for finding and downloading bathymetric data.
- In the Layers pane beside the map, uncheck all boxes except DEM Footprints.
- On the map, zoom to the East Coast of the United States. Zoom farther in to the mouth of Chesapeake Bay.
- On the map, click within the Virginia Beach rectangle.
- In the pop-up window, expand the NCEI Digital Elevation Models folder. Click Virginia Beach (1/3 arc-second).
The 1/3 arc-second measurement refers to the data's resolution.
- Click Link to Metadata.
A new page appears, containing detailed metadata for the Virginia Beach data.
- On the Access tab, next to Download Data, click Download NetCDF File.
NetCDF is a data format used for sharing array-oriented scientific data and is commonly used in oceanography.
If you are unable to download the file from the NCEI website, you can download and unzip this copy of the file.
The data will take several minutes to download. In the meantime, you'll download another DEM dataset.
- Download the Atlantic DEM.
This layer is a subset of another DEM dataset from NCEI. It was clipped to a smaller area to allow for faster download times in this lesson. You can find the metadata for the original dataset at U.S. Coastal Relief Model Vol.2 – Southeast Atlantic.
- When the Atlantic_DEM.tif file has downloaded, move it into your Ocean folder.
You created the Ocean folder earlier in the lesson, when you created the Ocean project in ArcGIS Pro.
It is not necessary to place this file in a specific folder, but it is best practice to keep all files related to a project in the project folder. This will make them easier to find later and to add to your map in ArcGIS Pro. Steps later in the lesson will assume this file is stored in your Ocean folder.
View a digital elevation model
The two files you downloaded are both digital elevation models, which means that they map elevation above or below sea level. However, they are stored in two different data formats: .nc (netCDF) and .tif. You'll add the .tif file to the map first and explore it.
- Open your Ocean project in ArcGIS Pro. On the ribbon, click the Map tab. In the Layer group, click Add Data.
- In the Add Data window, in the side panel, under Project, expand Folders and click Ocean.
- Click Atlantic_DEM.tif.
- Click OK.
If the Build Pyramids and Calculate Statistics window appears, click OK.
- In the Contents pane, right-click Atlantic_DEM.tif and click Zoom To Layer.
Black-and-white data appears on the map, covering the mouth of Chesapeake Bay and part of the continental slope. In the Contents pane, the legend ranges from -2883.1 to 20.
Because this is a DEM, these numbers represent elevation above and below sea level. You'll view the layer's properties to find out which unit the numbers are in.
- In the Contents pane, right-click Atlantic_DEM.tif and click Properties.
- In the Layer Properties window, click the Source tab. If necessary, expand the Data Source section.
The Vertical Units value is listed as meters.
- Close the Layer Properties window.
The legend shows that white areas are 20 meters above sea level, while black areas are 2,883 meters below sea level.
DEMs are important tools for understanding coastal areas. Some of their uses include modeling tsunami flooding and sea-level rise, managing ecosystems, and spatial marine planning.
- Pan and zoom to explore the data. Click any part of the data.
A pop-up appears, listing a Stretch.Pixel Value. This is the number of meters above or below sea level for the area you clicked.
- Close the pop-up.
Question 6: Describe the terrain visible in the Atlantic DEM layer.
- In the Contents pane, turn on the World Seafloor Geomorphology layer and drag it above the Atlantic DEM layer.
- Expand the World Seafloor Geomorphology layer and turn off all of the sublayers except Canyons.
On the DEM, canyons appear as dark lines leading from the high areas to the low areas. Many of these canyons were probably formed by rivers during the last ice age, when sea levels were much lower and the continental shelf was exposed as land.
- Zoom in to examine the canyons up close.
The DEM layer is raster data, meaning it is made of a grid, where each cell, or pixel, has as different value. The World Seafloor Geomorphology layer is vector data, meaning it is made of shapes (either points, lines, or polygons) that store attribute information.
- Collapse the World Seafloor Geomorphology layer and turn it off. Right-click Atlantic DEM and click Zoom To Layer.
Compare digital elevation models
Next, you'll add the DEM that you downloaded from NCEI and compare it to the .tif layer.
- When the virginia_beach_13_mhw_2007.nc file has downloaded, move it into your Ocean folder.
- In ArcGIS Pro, on the ribbon, click the Map tab. In the Layer group, click the bottom half of the Add Data button. Click Multidimensional Raster Layer.
Since netCDF files can contain multiple dimensions of data—for example, to record information at different times or depths—you need to choose which dimensions you want to display.
- For Input File, click the Browse button. Browse to the Ocean folder and choose virginia_beach_13_mhw_2007.nc. Click OK.
This netCDF file has only one dimension: Band 1.
- In the Select Variables table, check the box next to Band1. Ensure that Output Configuration is set to Multidimensional Raster.
- Click OK.
- In the Contents pane, click the virginia_beach_13_mhw_2007.nc_Band1 layer to select it. On the keyboard, press F2 to make the layer's name editable. Type Virginia Beach DEM and press Enter.
It may take a few moments for the layer to appear fully on the map. This layer is also a DEM. It uses a different color scheme than the other DEM, mapping high elevation in red and low elevation in blue. It covers a smaller area than the other layer.
You'll change the color scheme to make it easier to compare the two DEMs.
- In the Contents pane, under Virginia Beach DEM, right-click the legend. Click the color scheme menu and choose the Black to White color scheme. (Point to color schemes to read their names.)
The color scheme is backwards. You'll flip it so high elevations are white and low elevations are black.
- Right-click the legend again and click the Reverse color scheme button. Click outside of the color scheme window to commit the change.
The two DEM layers now use the same color scheme.
Question 7: In Atlantic DEM, there's no visible elevation change on the continental shelf: the entire area appears flat and white, so even the coastline isn't visible. Why does Virginia Beach DEM show so much more variation in the same area?
The area covered by the Virginia Beach DEM layer is already covered by the other DEM. However, it is higher-resolution data than your existing layer, meaning that it provides more information per square kilometer. This could be useful to parts of your analysis focused on shoreline features, so you will keep this layer as part of your project.
Question 8: How can you tell that Virginia Beach DEM has a higher resolution than Atlantic DEM?
- In the Contents pane, turn on the World Seafloor Geomorphology layer.
Near the south of the DEM, a break in the canyons is visible.
This area is named the Currituck Slide. It was caused by a submarine mass failure (SMF) that occurred between 24 and 50 thousand years ago. A SMF is an underwater landslide, and can be triggered by earthquakes, too much sediment, or gas seeps. SMF events are known to cause tsunamis, which are otherwise rare in the Atlantic.
If another section of the continental slope were to collapse, as the Currituck Slide did, it could cause a localized tsunami on the east coast of the United States. While SMF events are rare, simulations show that a SMF of the same size as Currituck in the same region would create run-up heights similar the storm surge of a category 3 or 4 hurricane. A tsunami's run-up or inundation height is the maximum elevation above sea level that the tsunami reaches on ground. High-resolution bathymetry and topography of the coastline, like that found in the Virginia Beach DEM layer, are important tools for modeling the threat from tsunamis.
Question 9: How is high-resolution elevation data for both the seafloor and land areas helpful for preparing for tsunamis?
- On the Quick Access Toolbar, click the Save button.
To learn more about the Currituck Slide, read Potential for large-scale submarine slope failure and tsunami generation along the U.S. mid-Atlantic coast.
In this lesson, you explored several sources of bathymetric data. You accessed GEBCO data with a WMS URL, the Oceans basemap via the basemap gallery, and a geomorphology map from ArcGIS Living Atlas via the Catalog pane. You downloaded two DEM datasets, one from the NCEI data portal. These are only a few of the sources of bathymetry data available online.
Exploring data portals and their datasets is a necessary step in almost every GIS project. Searching for relevant geospatial data is often time-consuming, but doing a thorough survey early in the process will make the rest of your GIS project easier.
- Are you allowed to use this data? How do you know?
- How should you acknowledge the data in your final project?
The data source should be acknowledged with the following text: Imagery reproduced from the GEBCO_2021 Grid, GEBCO Compilation Group (2021) GEBCO 2021 Grid (doi:10.5285/c6612cbe-50b3-0cff-e053-6c86abc09f8f). This information can be found on the GEBCO WMS page, under Data set acknowledgement.
- What are some similarities and differences between the WMS layer and the basemap?
Both layers contain a hillshade of the ocean floor and different shades of blue to represent ocean depth. The depth colors are bolder and more dramatic on the WMS layers, making it easier to visualize some features, such as the Puerto Rico Trench. The basemap layer includes labels for features such as canyons, banks, and depth measurements, which can help you to identify features or regions. The basemap is multiscale, meaning that more detailed information appears as you zoom in.
- What are some other features found in the area of the New England Seamounts? Make an observation about a geographic pattern visible from this data in this area.
The following are some examples of visible patterns:
- Canyons spread out like fingers from the edge of the continental shelf.
- Much of the study area is covered by a rise, which is a thick sloping bed of sediment abutting a continental margin.
- The seamounts and much of the slope coincide with escarpments. These steep slopes often overlay these features.
- What are some of the data formats available?
There are .pdf maps; CDs; netCDF files; grids available as ARC ASCII, Binary Float, GeoTIFF, netCDF, CRD98, and XYZ; multibeam files; and more.
- In Atlantic DEM, there's no visible elevation change on the continental shelf: the entire area appears flat and white, so even the coastline isn't visible. Why does Virginia Beach DEM show so much more variation in the same area?
The continental slope is the most prominent feature visible in the Atlantic DEM layer. Running north-south, it divides the study area into two different elevations. It is lined with canyons and slopes. The coastline is not visible.
- The elevation range of Atlantic DEM is much larger than Virginia Beach DEM (2,903 meters versus 85 meters). This allows for more detail and subtle elevation changes to be visible in Virginia Beach DEM, while in Atlantic DEM, the entire color range is reserved to show the dramatic elevation change at the continental slope.
- How can you tell that Virginia Beach DEM has a higher resolution than Atlantic DEM?
There are two ways to determine which layer has a higher resolution:
- Zoom in on each DEM until individual pixels are visible. Note the scale reported below the map. You must zoom in further to see the pixels in Virginia Beach DEM. You can also measure the pixels with the Measure tool.
- Right-click each layer and click Layer Properties. In the Layer Properties window, click the Source tab. Expand the Raster Information section. Note the values reported for Cell Size X and Cell Size Y: they are larger for Atlantic DEM, meaning that each pixel covers a larger area.
- How is high-resolution elevation data for both the seafloor and land areas helpful for preparing for tsunamis?
Tsunamis behave according to the laws of physics, with their travel time, speed (wave celerity), and amplitude (wave height) dependent on depth and shoreline configuration. The shape, direction, and impact force of a tsunami are especially dependent on the depth and breadth of the seafloor that it travels over. The nature of the damage that occurs on land will vary depending on the shoreline topography.