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Seeing the Seafloor Using Sound - Multibeam Sidescan Sonar

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You will use a motion detector to learn about the how sound waves can be used to "image" objects. The motion probe connected to a CBL interface to collect reflected sound data in real time to produce a graphical representation of their experimental seafloor.

In this experiment, you will:

  • use a TI Graphing Calculator, a CBL System, and a motion detector to measure distance
  • use a TI Graphing Calculator to produce a graph representing the seafloor
  • analyze and interpret graphs


  • CBL System (1 per group)
  • Meter stick (1 per group)
  • TI Graphing Calculator (you will need one TI-82, 83, 83+, 85, 89, or 92 per group.)
  • Masking tape (for marking their start and end points and to aid in securing string)
  • Bottles, Cans, Boxes, etc. (serve as the objects imaged on the seafloor)
  • Stools (2 per group)
  • String (2 meters per group)
  • Vernier Motion Detector (1 per group)

    Name___________________ Partner ________________ Date ____________

    1. Place five or more objects, (cans, bottles, boxes, etc) between two stools. The stools will serve as your start and end point. Use a meterstick to measure the distance between the two stools. This is an important measurement and should be done to the nearest centimeter. Record this distance in your data table.

    2. Stretch a sting tightly between the two stools approximately 1 to 1.5 meters above the floor. This string will function as your sea level reference.

    3. Connect the motion detector to the Sonic Channel of the CBL. (Plug the white end of the connect cable into the sonic port on the left side of your CBL. It will click when it is in properly.) Connect the CBL System to the TI calculator with the link cable using the small circular port on the bottom edge of each unit. Firmly press in the cable ends into the calculator and the CBL. Make sure that the cables are in tightly. Try not to bend the link ends. The motion detector will experimentally behave like a ship mapping the seafloor. Take a few practice runs with your motion detector. Start at one end of the string and move the detector the length of the string in three (3) seconds. Make sure that the detector speaker is not interfered by the string. Once you have mastered technique you are ready to collect data.

    4. Turn on the CBL unit and the calculator. On your calculator press PRGM and select PHYSCI from the menu. Scroll to the program using the up and down arrows on your calculator and press ENTER or push the number on your calculator that matches the number next to the PHYSCI program. Once you select the program, the calculator will display prgmPHYSCI on the screen. Press ENTER on the calculator. The new screen will have information about the program. Press ENTER as instructed on the bottom of the screen.

    5. You are now ready to up the calculator and CBL for use with a motion detector.

  • Select SET UP PROBES from the ***MAIN MENU***. (press 1 or scroll using the up and down arrows then press ENTER)
  • Enter "1" as the number of probes. Press ENTER.
  • Select #7: MORE PROBES. (press 7 or scroll using the up and down arrows then press ENTER)
  • Select MOTION from the SELECT PROBE menu. (press 3 or scroll using the up and down arrows then press ENTER)
  • At the ***MAIN MENU***. Select COLLECT DATA (#2) (press 2 or scroll using the down arrow then press ENTER)
  • Choose TIME GRAPH (#2) from the DATA COLLECTION menu. (press 2 or scroll using the down arrow then press ENTER)
  • Set ENTER NUMBER OF SAMPLES: to 30 Press ENTER. This will give you an experiment length of 3 seconds. Press ENTER as instructed on the screen.
  • At CONTINUE choose #1 USE TIME SETUP. (press 1 or scroll using the up and down arrows then press ENTER)
  • Position your probe at the starting point for your seafloor. Follow the instructions on the calculator screen and then move the motion detector along the length of your string to map your seafloor.
  • The calculator will store your data. The calculator will display TIME IN L1 SONIC IN L4, L5, L6. At this point press ENTER on your calculator.
  • Select DISTANCE from the SELECT CHANNELS menu. (press 1 or scroll using the up and down arrows then press ENTER). A graph of your data will be shown. Distance away from the probe is on the Y axis and time is on the X axis.

    6. REMEMBER, as you begin to collect data move the detector along the string as you practiced. As you move the motion detector will send out a sonic pulse that will be reflected off the surface of any object that it hits. Slowly move the probe from one stool to the other as the probe is running. Have the calculator to graph your data as distance versus time graph.

    7. Sketch your distance vs. time graph for your seafloor data into your report or print it out using the TI Graphlink. Check with your teacher to see which method to use.

    8. Describe the shape of your graph. Compare the graph to the actual height and shape of the objects on your seafloor. To do this, measure the height of each object at specific distances along the length of the string and construct a graph of vertical height versus horizontal distance from these measurements. Notice that the two graphs are 180 degrees opposite to one another. Discuss with your teacher how you will resolve this problem.

    9. Repeat the procedure with a new seafloor. The teacher will construct an area in a darkened room. You will have to use the data you collect to predict the size and shape of the objects from your model seafloor.

    Discussions Questions/Extensions ......

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