Physical Oceanography
Combined Homework and Laboratory Set 2
Due 3 February 2004

Late work will cost 15 points per week or part of a week it is late

The goal of this laboratory is to learn more about the sea floor, how it is mapped, and sources of bathymetric data. You will use information and maps available through the internet plus information in the class notes. The work can be completed using any computer with a web browser and access to the Internet. The work should take about three hours to complete.

The shape of the sea floor is important to physical oceanography. The shape of the sea floor, and the depth of water influences circulation in the ocean. Sills separate deep ocean basins, sea mounts disrupt currents and tidal flows and this helps mix the ocean waters, and the relative thinness of the water constrains the flow to be mostly two-dimensional.

The Problems

Please help Captain Nemo and Professor Numero Uno solve their problems. In writing your report to them:

1. Please document and justify your recommendation.
   
2. This includes, but is not limited to:
   
   • What information do they need from the maps or data sets of ocean depth?
   • Which maps or data sets did you consider?
   • Which maps or data sets can provide the information needed by Captain Nemo and Professor Uno?
   • Can you trust the map or data sets? That is, can you recommend a particular map or data set with high degree of confidence?
   
   
3. You do not have to answer the questions in the lists of maps. I recommend you use the questions to test your understanding of the data sets before you write your reports.

Problem 1

Captain Nemo must take his submarine from offshore Manila to offshore Seattle while staying submerged at 1000 m. He asks you, his navigation team, what maps, charts, or data set he should use to avoid running aground on a seamount. He points out he must make the journey without using sonar, and that the on-board inertial navigation system knows the submarine's position with an accuracy of 1 km in the horizontal and 1 m in the vertical.

Problem 2

Professor Numero Uno has a contract to develop a global, numerical, model of the ocean's circulation. The model requires oceanic depths every 0.25° of latitude and longitude. What data set should he use and why? Please contrast and compare the recommended data set with other possible data sets.

Sources of Information

Deep-ocean mapping in this country is coordinated through the NOAA National Geophysical Data Center. who provide on-line access to the General Bathymetric Charts of the Ocean, Maps from satellite altimetry, and general bathymetry and topography maps. You may want to look at their list of bathymetric products. Click on the Info box brings up documentation about each product, including references to published papers describing the product. Much of what you need can be obtained through them, or from web pages linked from their site. Access

Global Seafloor Topography from Satellite Altimetry

For many purposes, the most complete and accurate global maps of the sea floor are those produced by combining satellite altimeter and ship echo-sounder data. If you want to learn more about the maps and how they were produced, read Sandwell and Smith's paper on Global Bathymetric Prediction for Ocean Modeling and Marine Geophysics and go to NGDC/WDC A for MGG - Predicted Global Seafloor Topography Information and read the paper on Exploring the Ocean Basins with Satellite Altimeter Data by Sandwell and Smith on how altimeters are able to observe bathymetric features. You may also wish to read Section 3.4 of the on-line textbook.

In preparing to answer problem one and two, please answer these questions on a separate page:

1. Are data from the World-Wide ship echo-sounder data base sufficient to map all important sea-floor features?
2. What important subsea feature or features were missed in the example cited in Sandwell and Smith's paper on Global Bathymetric Prediction for Ocean Modeling and Marine Geophysics? Can you cite specific examples?
3. Where are the missing features located? Note latitude and longitude and name of the oceanic area.
4. Who distributes global bathymetric data sets based on altimetric and ship data? In what form are they distributed?
5. What oceanic areas were NOT mapped by this technique?

Some important maps are:

1. The 5 Minute Topographic Map ETOPO-5 was produced from ship echo-sounder data.
   • What is contained in the data set?
   • What is the original source for data in the set?
   • Who collected, edited, and processed the original data used to produce the data set?
   • Over what times periods were data obtained?
   • Over what area?
   
   
2. The 2 Minute Map of Earth ETOPO-2, replaces ETOPO-5.
   • How does this map differ from the ETOPO-5 maps?
   • Is it more accurate, or more complete?
   
   
3. The General Bathymetric Chart of the Ocean GEBCO and regional GEBCO charts are produced by digitizing hand drawn contour plots of depth calculated from echo-sounder data by international teams of hydrographers.
• How does this map differ from the ETOPO-5 and 2-Minute maps?

Revised on: 18 June, 2008