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2500m isobath + 100M constraint
Computing the 2500m isobaths is necessary in order to determine the Depth constraint in UNCLOS Article 76, which is the 2500m isobaths plus 100 nautical miles. The 2500m isobaths can be generated based on bathymetry grids or on bathymetric profiles (from single beam bathymetry). The only ones that can be used for an actual submission to the CLCS are 2500m isobath points generated from real bathymetry data. For a grid, the resulting 2500m isobath will be a contour line. A bathymetric profile will produce one or more points wherever the profile value is 2500m.
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Generate the 2500m isobath from a Seabed Surface- Locate the etopo1 dataset which is located in 2. Seabed / Grids. The dataset should have the schema Seabed Surface. If it does not have this schema, right click it and select Set schema > Seabed Surface.
- Right click the dataset and select Display 2500m isobath. Black lines will appear where the 2500m isobaths are located. You may notice that the isobaths cover a larger area than you are interested in so we will restrict the area where the isobath is calculated.
- Set the display window to 2D mode by clicking the 2D View button.
 Image Added or typing 2 on the keyboard. - Zoom the display window so that it only covers the area you are interested in.
- Right click the seabed surface and use the command, Generate 2500m Isobath. This will use the full resolution of the grid and calculate the 2500 isobath only in the area we are focused on. If the display window is in 3D mode it will create the isobaths for the entire dataset. If it is in 2D mode it will only create the isobaths inside the display window.
- Locate the result dataset which should be in 2. Seabed / 2500 Isobath. The Isobath dataset you have created may still have some line pieces which you want to remove before generating the 100M line, for instance the pieces that are seaward of the FOS points.
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Edit the generated 2500m isobath- Clear the display window by clicking the Image Added button in the main toolbar.
- Right click the dataset and select the command Edit points and lines.
- Click the Display button near the bottom of the Edit points and lines dialogue box in order to see the isobaths.
- Select the Delete tab.
- Inside the Delete tab, select By closed line.
- Click the start button, then digitize a closed polygon around the part you want to delete by clicking with the left mouse button.
- Click Connect to Start and End in order to connect the last digitized point with the start point, and end the digitizing.
- Click Delete points INSIDE.
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The part inside the closed polygon is now deleted. You may repeat the three last points in order to delete some more. The changes you make are not performed on the dataset directly, but as a local copy. In order to store the changes in the Edit points and lines menu, click the Execute button at the bottom. A new copy of the data set is stored in the folder. - Click the Cancel button in the Edit points and Lines menu.
- Clear the display window again.
- Display the edited isobaths and confirm that the unwanted parts have been removed.
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Generate 2500m isobath + 100M constraint line- Display the 2500m isobath which you created in the previous exercise.
- Right-click the isobath and select the command Generate 100M Line.
- The new line should now be available under 1. Maritime Lines/100M Lines.
- Display the 100M line.
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Download the ETOPO1 grid from the Internet- Open a web browser, and go to the following address: http://www.ngdc.noaa.gov/mgg/global/global.html
- Click the link: Extract Custom Grids - in the left column on the page, below the globe. A new web page with a interactive map should appear.
- Zoom into the area where you want to extract the grid.
- Click the icon with and i in the upper left corner of the map window.
- Drag a rectangle over the area where you want to extract the grid. You should see a red rectangle on the map.
- Keep Layer as ETOPO1 (ice)
- Select Output Format XYZ
- Click "click here to download"
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Convert the grid to Mercator coordinate systemThe data is imported in Geodetic, with latitudes as Y coordinates and longitudes as X coordinates. In order to view the grid with the data we have already imported and converted to a Mercator coordinate system, we need to convert this grid to match the same coordinate system as the other data in the project (Mercator). - Click the dataset and go to the Shared commands section in the Toolbox.
- Double click the Convert to Mercator... command in the Operations folder. (or another relevant datum / coordinate system)
- Change the result combo box to Replace input.
- Click Execute.
- Agree to replace the existing dataset by clicking Yes.
- Geocap will report if the grid has been converted correctly, click OK and close the conversion dialog by clicking Cancel.
- Check that the schema of the dataset is seabed surface. If not then right click the dataset, choose Set Schema and choose seabed surface.
The data is now converted and ready to be displayed: - Right click the dataset and select Zoom to Data
- Right click the dataset and select Map Sea
- Right click the dataset and select Map Land
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When you have made changes to the project it is always a very good idea to store them. Click the save button Image Removed in the project tool bar in order to save your project.
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Generate a Bathymetric Profile from a grid- Locate the dataset you imported in the previous exercise, which should be located in 2. Seabed / Grids. The data set should have the schema Seabed Surface. If it does not have this schema, right click it and select Set Schema > Seabed Surface.
- Display the seabed by right clicking it and selecting Map Sea.
- Right click the dataset and select the command Display contours...
- A menu will appear. We will just use the default settings. Click Execute, and Cancel.
- Right click the dataset and select the command Generate Bathymetric Profile. A menu will appear.
- Click the Start button, then digitize the first point of the profile by clicking with the left mouse button where you want the profile to start on the seafloor in the display window.
- Digitize the last point of the bathymetric profile by clicking with the left mouse button where you want the profile to stop on the seafloor.
- After you have digitized both the start and stop point, you will be prompted with a dialog asking you to provide a name for the profile. Keep the default name and click OK.
- Geocap will notify you where the resulting Bathymetric profile has been stored in the project. Click OK.
- Locate the new profile in 2. Seabed / Bathymetric Profiles; this is the default position of bathymetric profiles. In order to structure our project we want to move the profile into a sub folder and rename the profile.
- Right click the folder 2. Seabed / Bathymetric Profiles and select New > Folder.
- Change the folder name to Etopo1 and click OK.
- Right click the profile and select Cut.
- Right click the new folder and select Paste. The profile is now moved into the new folder.
- Right click the data set and select Rename. Give the profile a suitable name, for example the name of the area you are working in.
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