I. Gardiner Points

Owned by Harald Sund (Unlicensed)
Last updated: Oct 16, 2015 by Tore Sannes (Unlicensed)
3 min read

Introduction

In the previous section we calculated sediment thicknesses. In order to apply the sediment thickness formula (Gardiner) in UNCLOS Article 76, we need to compare the sediment thickness with the distance to the foot of slope. When working with 1% sediment thickness points it is often useful to experiment with different datasets and settings. You might for example change the velocity model and see how that effects the final Gardiner points, or you might try to change the FOS points to see if that has any effect on the final result. In this section we are going to experiment with different percentages, instead of looking just at 1%, and see how much this affects the calculations.

Exercises

 

Visualizing 1% sediment thickness points

The Generate > 1% of distance to FOS Area command uses a FOS dataset as input to the calculation. This can be a single FOS point or a group of many FOS points. Geocap will automatically find the FOS point which is closest to any sediment thickness point and then do the 1% calculation. Since all our profiles are located in the Northern Plateau we know that our Northern Plateau FOS points will be the closest, so we will use this dataset.

Exercise

Display sediment thickness points > 1% of distance to FOS

  1. In the folder 3. Sediment Data / Sediment Profiles right click the profile ATL-LOS-00-2 and click Generate > 1% of distance to FOS Area.
  2. Click the browse icon, browse for the Northern Plateau dataset and click OK.
  3. Make sure the Display as cross section is checked.
  4. Uncheck the Store in project box.
  5. Click Execute.
  6. Examine the result. Points thicker than 1% of the distance to the nearest FOS point will display the sediment profile in green. Points less than 1% distance to FOS is displayed in red.


Sediment profile showing thickness more (green) and less (red) than 1% of the distance back to FOS

 

You now have a set of Gardiner points, but what would happen if you changed your interpretation, velocity model or FOS points? What is the uncertainty of the sediment thickness? An easy way of visualizing how "stable" your Gardiner points are is to change the percentage of distance to FOS.

Exercise

Use different percentages to calculate x% sediment thickness points

  1. Change the Percentage of distance to FOS to 1.1%.
  2. Keep the rest of the settings and click Execute.
  3. Investigate the result. Did it change? In which direction? Why?
  4. Change the Percentage of distance to FOS to 0.9%
  5. Keep the rest of the settings and click Execute.
  6. Investigate the result. Did it change? In which direction? Why?

 

 

It is also possible to look at the uncertainty of your sediment thickness by increasing or decreasing it with i.e 10%. This can be done using the Function command and multiplying the sediment thickness points with 1.1 or 0.9.

Saving 1% sediment thickness points

We now want to store our Gardiner points as a separate dataset so we can continue to work with them.

Exercise

Store the 1% sediment thickness (Gardiner) points

  1. Change the Percentage of distance to FOS back to 1%.
  2. Check the box Store in project.
  3. Make sure Display as cross section is checked.
  4. Click Execute.
  5. A new data set will be created in 3. Sediment Data / Sediment Thickness Points. Click OK.
  6. Repeat the process for all sediment profiles.
  7. All profiles should now be displayed with green and/or red colors representing more than 1% sediment thickness and less than 1% sediment thickness.

 

The 1% sediment thickness (Gardiner) points datset contains a lot of relevant metadata, like which FOS point was used in the calculation, the exact percentage, the shot point, the distance in meters etc. This is information that should be documented in the final submission.

Exercise

Examine the metadata for sediment thickness points

  1. In the folder 3. Sediment Data / Sediment Thickness Points right click the ATL-LOS-00-2 Gardiner points and click Table View.
  2. Observe that that each 1% sediment thickness point refers back to a bathymetric profile and a FOS point. It also reports the thickness, shot point, distance in meters and percent of distance to FOS.
  3. Identify the Gardiner point furthest away from the coastline, it should be the last one in the table. Tip: Check the Display marked points box and select the last point in the table.
  4. Which FOS point contributed to this Gardiner point? What is the percentage of the distance back to this FOS point?