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Name Date Oceans 11 Bathymetry and the Use of Technology Our knowledge of the diverse topography of the ocean floor is relatively recent. Up to the 1920’s depths to the ocean floor were determined by lowering a weighted rope until it touched bottom and then measuring the length of the rope. Ocean floor composition was essentially inferred from information obtained close to shorelines. Knowledge of the seafloor remained scant until the technological breakthroughs of the latter part of the twentieth century. Today oceanographers have numerous tools by which to decipher the topography of the ocean floor. The process of unmasking the ocean floor features is termed Bathymetry. To learn more about the technology used, go to the following website and answer the questions below. http://geosun1sjsu.edu/~dreed/130/lab/1html http://oceansjsu.com/105d/exped_mapping/3.html 1 The vast majority of the Earth’s surface lies underwater, far under the sea surface. Most of the sea floor lies 4 to 5 kilometers below the surface of the ocean. The seafloor consists of a combination of flat plains covered with mud, volcanic ridges and isolated volcanoes, deep-sea trenches, submarine canyons and the margins of continents. Why is it important to know about the shape of the seafloor? 2 What is hypsometry? To be able to solve the mystery of the Earth’s formation Global shipping and communications industries depend on this information for the safe speedy exchange of goods, people, and information Submarines, airplanes and missiles need it to travel an accurate course Analysis of the shape of the Earth’s surface in terms of elevation 3 Satellite altimetry is where satellites use radar to measure the distance to the sea surface. Using the website diagram, draw a picture showing the basis of the technique. Please colour it. In the second space, explain. 4 What does the shape of the sea surface tell us about the seafloor? 5 How do we “see” the seafloor from the surface of the ocean? Use pencil crayons to colour it in. Electromagnetic energy (radar), in the frequency range of billions of cycles per second, is transmitted from a sensor on the satellite, travels to the ocean surface and bounces back to the satellite. The time it takes the energy to return to the satellite is used to measure the distance to the sea surface very precisely (within accuracies of less than an inch!) The Earth's gravity field piles up water over top a seamount causing the sea surface to mimic the shape of the seafloor, once the effects of water temperature and surface currents (which also change the shape of the sea surface) are removed. Draw a picture showing the use of sound waves to produce images of the seafloor (referred to as ‘Echo Profiling or Echo Sounding’). In the second block, give a short explanation. In oceanography, sound waves are produced by an instrument, which is either towed on a cable behind the ship (as we will see later) or attached to the bottom of the ship (as shown above) The sound travels down into the water, echoes (bounces or reflects) off the seafloor and returns to the surface of the ocean where the timing of its arrival is detected at the bottom of the ship. 6 One the Expedition Menu, find ‘7. Traveltime’ What is meant by the term “two-way travel time”? Time between the creation of each pulse of sound and the reaction of the echo from the seafloor to the sea surface What is the equation used to calculate the velocity of an object? Write it in words and symbols. V = d What is the average speed (velocity) of sound in water? 1500 meters/second Convert the velocity equation to an equation which allows you to calculate the water depth from an echo-profiling record. Determine the water depth if the signal sent out by an echo sounder requires 6 seconds to strike bottom and return to the recorder. Show all work. If the two-way travel time for the signal is 4.4 seconds, how deep is the ocean floor? Show all work. What is the two-way travel time for an echo to traverse a path from ship to water depth of 3000 m and back to ship? Show all work. t or 7 In this section, we are going to talk about multi-beam and side-scan sonar. (#10) Many beams of sound are sent off in all directions. It allows one to see a larger area of the seafloor, many miles wide, instead of the portion directly beneath the ship (echosounding). What is multi-beam sonar? In what way is the knowledge obtained by multi-beam sonar used? Side-scan sonar was the technique use to find the wreckage of the airplane carrying John F. Kennedy Jr. and his wife and sister-in-law a few years ago. How does side-scan sonar differ from multi-beam sonar? If you wanted to measure, in detail, the shape of the seafloor, what would be the best technique to use? Conclusion What did you learn from this activity? What part did you most enjoy? Environmental assessments, to further our understanding of the seafloor and the natural or human factors that shape it To assist in navigation of ships To determine fish habitats and locate minerals on the seafloor Produces photo like images of seafloor (used for searching and detecting objects) Does not directly measure water depth like multi-beam does Multi-beam sonar