Introduction
The use of bathymetry is a very central element when working with the determination of the extension of the continental shelf according to UNCLOS Article 76. It is relevant both for the depth constraint (2500m depth +100M) and the determination of the foot of the continental slope.
In Geocap bathymetry can have several different forms:
- Singlebeam bathymetry data may be imported as bathymetric profiles.
- Multibeam bathymetry soundings or other spread point data with depth measurements can also be imported. In order to use the foot of slope analysis tool on point data, the dataset must be gridded first. This can be done in Geocap.
- Grids may be imported directly into Geocap. Geocap supports import of several different grid file formats; the most common and useful kind of bathymetric data is the ETOPO1 grid. The ETOPO1 Grid is provided by NGDC (National Geophysical Data Center). This grid . Most Shelf projects will consist of a low resolution grid (i.e Etopo or SRTM) covering the whole area of interest and then smaller high resolution grids from multibeam data.
The Etopo or SRTM grids will not be accepted by the Commission as a basis for your foot of slope points. However once you have imported the grid you will be able to see the shape of the sea floor, and in particular the approximate position of the Foot of Slope or base of slope region.
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Generate 2500m isobath + 100M constraint line- In the folder 2. Seabed / 2500 meter Isobath right click atlantis's 2500 meter isobath and select Generate 100M Line.
- Keep the default settings and click Execute
- The new line should now be available under 1. Maritime Lines/100M Lines. Click OK.
- In the folder 1. Maritime Lines/100M Lines display atlantis's 2500 meter isobath + 100M
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Bathymetric Profiles
Bathymetric profiles To determine the foot of the continental slope shall be determined as the point of maximum change in the gradient at its base.we need bathymetric profiles. These profiles will be used as input to the bathymetric profile analysis tool in the next chapter. Bathymetric profiles can be imported from single beam or generated from bathymetric grids. In this tutorial we will use the atlantis seabed surface grid (similar to Etopo1) to generate bathymetric profiles. The project already contains several bathymetric profiles grouped into different areas. Our task is to complete the foot of slope analysis in region called East Sea.
Image Added
East Sea is the area in red
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Generate a Bathymetric Profile bathymetric profile from a grid- Locate Display the dataset you imported in the previous exercise, which should be located atlantis seabed surface dataset 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 Seaand zoom in to the East Sea area.
- 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 atlantis dataset again 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
- Click Stop
- You will be prompted with a dialog asking you to provide a name for the profile. Keep Keep the default name and click OK.
- Geocap will notify you where the resulting Bathymetric profile has been stored in the project. Click Click OK.
- Locate the new profile in 2. Seabed / Bathymetric Profiles; this . 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.
- Display the profile.
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Generate more bathymetric profiles in the East Sea areaRepeat the steps in the previous exercise and generate a few more profiles in the same area. You should have 3-5 profiles in the area. |
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Group your bathymetric profiles into a folder- Right click the folder 2. Seabed / Bathymetric Profiles and select New > Folder.
- Select Generic and type in the name East Sea.
- Change the folder name to Etopo1 and click OK.Click OK.
- Right click the East Sea folder and select Set Schema > Bathymetric Profiles
- Locate the profiles you generated in 2. Seabed / Bathymetric Profiles.
- Select all the profiles, right click and select Cut
- Right click the profile and select Cut.
- Right click the new East Sea folder and select Paste. The profile is now moved into the new folder.
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Rename your bathymetric profiles- Right click the data set one of the profiles in the East Sea folder and select Rename. Give the profile a suitable name, for example the name of the area you are working in
- Type in the name East Sea 1.
- Continue to rename the other profiles in the same manner. East Sea 2 etc.
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It is smart to name the profiles so the number increases with the profiles location south to north. |
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