Table of Contents Module 10
PROCEDURE 1. Ask students what they know about sonar, and provide additional information as necessary.
2. Be sure students understand that sonar (which stands for Sound Navigation and Ranging) uses an acoustic signal or pulse of sound that is transmitted into the water by a sort of underwater speaker known as a transducer. Transducers may be mounted on the hull of a ship, or may be towed in a container called a towfish. If the seafloor or other object is in the path of the sound pulse, the sound bounces off the object and returns an “echo” to the sonar transducer.
3. The time elapsed between the mission of the sound pulse and the reception of the echo is used to calculate the distance of the object.
4. Some sonar systems also measure the strength of the echo, and this information can be used to make inferences about some of the reflecting object’s characteristics. Hard objects, for example, produce stronger echoes than softer objects.
5. Sonar systems can be used to determine water depth, as well as to locate and identify underwater objects.
6. A multibeam sonar system uses multiple transducers pointing at different angles on either side of a ship to create a swath of signals. The time interval between signal transmission and return echo arrival is used to estimate depth over the area of the swath. In addition to high-resolution maps, multibeam data can be used to create three dimensional models or even “fly-through” videos that simulate a trip across the area being mapped.
7. You may want to show this “before and after” image provides a glimpse of Okeanos Explorer’s EM302 mapping system capabilities in deep water.
8. The top image shows what we previously knew about the seafloor terrain in the southern Mariana region from satellite altimetry data. The bottom image includes an overlay of the information provided by the ship’s EM302 multibeam system. Image courtesy of NOAA Office of Ocean Exploration and Research.
9. Sonar provides an overall exploration strategy, and provides the “big picture” view as explorers look for anomalies.
STUDENT PROCEDURE
1. Your Beam Team should include three or four students, and each student should have two Sounding Rods. You will use these Rods to measure the depth under each of the holes in the lid of your box, then you will plot these depths to create a three-dimensional model of the landscape hidden inside the box. Each student will be responsible for measuring the depth of two or three of the holes in each row. If you stand in a circle (or part of a circle) around the box, you should all be able to make your measurements at the same time.
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