Hi Schmodellers,
For those of you who might be interested in obtaining high resolution bathymetric data, I highly recommend you approach the Council of Geosciences; they are extremely helpful and resourceful. From what I have learned they are very keen on getting more involved with the universities and students.
The bathymetric data I received for False Bay was primarily fair chart derived so the density of the data varied throughout the domain, high data density was located in the bay and low density further offshore. The data needed to be gridded. In my case, as a result of the coarser resolution of the bathymetry further offshore, I had to grid the data into 100m cell sizes. See below, for a ‘zoomed in’ section of the end product compared with the GEBCO 1’ dataset.
In particular you will notice that the GEBCO dataset excludes the features located at the mouth of the bay, namely Rocky Bank and Rough Bottom. From the ROMS simulations that I have run, first with a flat bottom and then with the high resolution bathymetry, the results have shown that these features significantly influence the circulation and thermal structure in the bay. They reduce the inflow of remotely forced circulation and furthermore act as a barrier reducing the amount of cold bottom water that enters the Bay. The results highlight the importance of using high resolution bathymetric data in this study.
If you are interested in getting bathymetric data or want to know more contact Michael Machutchon michael@geoscience.org.za from the Council of Geosciences. If you would like to see my code for gridding the data please don't hesitate to ask.
Great job Sarah! This is really useful information!
ReplyDeleteDo you know how far off-shore the Council of Geoscience bathymetry data extends?
Thanks Bjorn,I am actually not sure. I had my False Bay Bathymetry blinkers on when I went there. I know for sure that the resolution of the data further offshore is much coarser. Perhaps give Michael an email he is very helpful.
ReplyDeleteThat sounds like some really interesting results and its great to know about the access to higher res bathymetry!
ReplyDeleteCGS recently had a meeting about extending offshore, Fiona made a nice summary of the meeting, which I can email to anyone interested, basically: The Council for Geoscience (CGS) have been requested to develop a business case for a systematic offshore mapping programme. They are consulting with the broader marine community to gain input and support for this jointly beneficial project. CGS is in direct contact with the DG’s of all the relevant government departments (DAFF, DEA, DME, etc) as the whole project hinges on support at the highest level.Less than 0.5% of our territorial water is publicly available in the form of marine geological charts.
Technologically, CGS is able to offer single and/or multibeam echosounders, sidescan sonars, seismic equipment, grab samples and corers. The echosounders are typically used for obtaining bathymetry data, with the multibeam offering better resolution, but at a greater cost. Sidescan sonar is used for sea floor imaging and acoustic texture maps. Together, echsounders and sidescan sonars produce quality geological maps with a 3D profile. Seismic equipment is used for sub-bottom profiling such as for researching the paleodrainage of rivers. Grab samples or corers can be used for ground truthing.
If a survey was to be done of the territorial waters using a multibeam echosounder, the survey would take at least 16 years working round the clock, 24/7. This is not a short term project. To cut cost and time it makes sense to combine efforts and resources of all participating stakeholders.
So, overall way forward:
1. Create inventory of what is already available and publicly accessible.
2. Assess where there are gaps, and their importance to the stakeholders.
3. Assign priority to the gap areas based on “value” (which need to be calculated in some way)