MAR 110 Natural Hazards & the Oceans

Tutorial #2

Ocean Floor Bathymetry

Instructor: Prof. Dan MacDonald(dmacdonald@umassd.edu; 508-910-6334; ATT 325)

TA: Georgia Kakoulaki(gkakoulaki@umassd.edu; 508-910-6366; ATT 325)

Bathymetry: Greek roots bathys- that means depth and- metry that means the process of measurement.

Bathymetric maps represent the ocean depth as a function of geographical coordinates in the same way topographic maps represent the altitude of Earth's surface at different geographic points.

Map Scale: the ratio between a distance on a map and the corresponding distance on the earth, often represented as 1:80,000 (natural scale) or 30 miles (48.27 kilometers) to an inch.

Isobaths: lines drawn on a map or chart that connect all points with the same depth below a water surface.

Slope: is the ratio of change in depth of a sea floor feature to the horizontal distance over which the slope is measured

Slope= change in depth/horizontal distance of slope

Velocity=distance/timeDistance=2*depth=velocity*time

(down and up) (known) (measured)Depth=(velocity*time)/2

Echo Sounding Record

Echo Sounding

An echo sounder or fathometer is a scientific device which is used to determine the depth of the ocean floor

Papua New Guinea

Contour lines follow paths of constant elevation and are closely spaced on steep slopes and widely spaced on relatively flat terrain

• Contour lines never split or cross, but may merge, indicating a very steep place

• Contours should always point upstreamin valleys

• Contours should always point downridge along ridges

• Adjacent contours should always be sequential or equivalent

• Contours should never split into two

• Contours should never cross or loop

• Contours should never spiral

• Contours should never stop in the middle of a map

Contour the Sandy Harbor

soundings at 1 fathom

intervals

Questions

What is the depth at

point A in

fathoms? _________

meters? _________

Where is the deepest

part of the bay?

Remember: 1 fm = ~2 m

What is the relief (or depth

difference) between points A

and B? ______________

What is the distance in km

between A and B? (draw a line

between them, measure it, and

then hold ruler up to the legend)

Determine the slope of the

bay from points A to B as

indicated below: __________fathom/mi

__________ft/mi

__________m/km

Remember:

slope = relief/horizontal distance

Use your conversion factors!

We have just gone over Exercise A (Sandy Harbor Chart).

Use same techniques for Exercise B (Pacific Ocean Chart: more challenging).

Contour interval for Ex. B is 200 meters

Homework #2 due Tuesday, Sept. 21

What is backscatter? Do you know any other instruments (except echo sounder) that uses the same method for measurements in the ocean????

If you have more saline water, does it effect the measurements of the echo sounder???

http://www.punaridge.org/doc/factoids/Sound/Default.htm

http://www.divediscover.whoi.edu/tools/sonar-singlebeam.html

http://serc.carleton.edu/eet/seafloor/orig_case_study.html

http://www.dosits.org/science/soundmovement/speedofsound/

http://oceanworld.tamu.edu/resources/ocng_textbook/chapter03/chapter03_06.htm

http://adventure.howstuffworks.com/outdoor-activities/hiking/how-to-read-a-topographic-map3.htm