PERFORMANCE ASSIGNMENT                                 

Mapping the Seafloor with Sonar

Background

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You have been hired by the telecommunications company, Talk To Me, to find an unobstructed relatively level path across the seafloor where they can lay down fiber optic cable. Naval records show that the submarine U.S.S. Bathy sunk somewhere in this area during World War II. The box before you represents an unexplored area of the deep seafloor. You will be using sound to "see" the features of the seafloor. Oceanographers at sea use Sonar equipment which sends out sound waves that are directed straight down towards the seafloor, reflect off, and return to the boat. If you know the round trip time for the sound pulse, you can calculate the one-way time. If you know the one-way time you can calculate the distance the wave traveled using a simple rate equation (speed = distance/time). The speed of sound in water varies depending on the temperature, salinity, and pressure. However, for this activity we will assume the average speed of sound in water to be 1500 meters per second. That’s 3300 miles per hour. Compare that to the speed of sound in air that is 760 miles per hour.

Procedure

    1. You will use the dowel as an instrument to measure the time it takes for a sound pulse sent from a ship to make a round
        trip to and from the seafloor. The dowel is marked with numbers that represent the amount of time it will take to hit
        a surface. Each inch marked on the dowel represents approximately 0.7 seconds which equals about 1000 meters.
        Gently insert the dowel into each grid hole until it hits bottom. Record the "time" from the dowel. The time represents
        the roundtrip for the sound pulse.

    2. Table 1 below shows the grid system on the top of the 15-hole box lid. The first table is to be used for trial 1 where
        you will collect times at only the specified coordinates. The coordinate system is similar to the game Battleship.
        Systematically go through the grid filling in the corresponding times in the empty boxes of Table 1 (Time). Complete #1
        in the Analysis section.

    3. For Trial 2 flip open the 15-hole lid. You will see below it a lid with 60 holes. Follow the same procedure as you did
        for Trial 1. Record the time data in Table 3. Complete #2 in the Analysis section.

Data

 
A
B
C
D
E
2
 
 
 
 
 
4
 
 
 
 
 
6
 
 
 
 
 
Table 1: 15 Stop Search Pattern (TIME(s))


 
A
B
C
D
E
F
G
H
I
J
1
 
 
 
 
 
 
 
 
 
 
2
 
 
 
 
 
 
 
 
 
 
3
 
 
 
 
 
 
 
 
 
 
4
 
 
 
 
 
 
 
 
 
 
5
 
 
 
 
 
 
 
 
 
 
6
 
 
 
 
 
 
 
 
 
 
Table 3: 60 Stop Search Pattern (TIME(s))

Analysis

    1. Sound travels through water at a speedy 1500 meters per second. Use the equation

    speed = distance ÷ time

        to solve for distance. Take into account that the times you recorded are the round trip times. The distance
        calculated is equivalent to the depth of the seafloor at that measured location. Calculate the depth (distances)
        for all your data points and record the values in the data table below.

     
    A
    B
    C
    D
    E
    2
     
     
     
     
     
    4
     
     
     
     
     
    6
     
     
     
     
     
    Table 2: 15 Stop Search Pattern (Depth(m))

        Have you found the submarine? If so list the coordinates where you found it. Return to Step 3 in the Procedure.



    2. Again use the equation, speed = distance ÷ time to solve for depths (distance) considering that sound travels at
        1500 meters per second. Take into account that the times you recorded are the round trip times. Calculate
        the depth (distances) for all your data points and record the values in the data table below.

     
    A
    B
    C
    D
    E
    F
    G
    H
    I
    J
    1
     
     
     
     
     
     
     
     
     
     
    2
     
     
     
     
     
     
     
     
     
     
    3
     
     
     
     
     
     
     
     
     
     
    4
     
     
     
     
     
     
     
     
     
     
    5
     
     
     
     
     
     
     
     
     
     
    6
     
     
     
     
     
     
     
     
     
     
    Table 4: 60 Stop Search Pattern (Distance(m))

    3. To get an idea of the underwater terrain draw in bathymetric lines (depth contour lines) that connects points of equal
        depth. Systematically move across each row of your Trial 2 depth data and for each depth look on the depth color
        table below to find the corresponding color. Color the appropriate square that color on the Seafloor Mapping Sheet.
        For example, if square A2 is 2500 meters deep then color section A2 green on the Seafloor Mapping Sheet.
    Depth (m)
    4500
    4000
    3500
    3000
    2500
    2000
    1500
    1000
    Black
    Purple
    Dark Blue
    Light Blue
    Green
    Yellow
    Orange
    Red
    Pink

        For 20% extra credit, map the seafloor using Excell. Obtain the procedure HERE.

    4. Analize your map:

      1. Now have you found the submarine? If so list the coordinates where you found it.



      2. Think about how this area might have formed geologically. Do you see evidence for converging or
          diverging plate boundaries? Explain.



      3. What differences did you have between your 15-hole "picture" and your 60-hole "picture"?



      4. Below is an area of seafloor that you want to map. You are the captain of the ship. What will be the best
          way to cover every square without passing over any square twice? Draw arrows to mark your path.



      5. What is your recommendation to Talk To Me in terms of placement of their pipeline for fiber optic cable?
          Explain your reasoning.



      6. Look at your bathymetric lines map. Which face of the mountain is the steepest and how do you know
          just by looking at the bathymetric lines?



      7. Why does sound travel faster in water than in air?