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Seeing the Seafloor Using Sound - Multibeam Sidescan Sonar

data | hook | main | background & resources | student

Author Contact Information

Steven Stevenoski
Lincoln High School
Wisconsin Rapids, Wisconsin

Students will use a motion detector to learn about the how sound waves can be used to "image" objects. They will use the motion probe connected to a computer-type interface to collect reflected sound data in real time to produce a graphical representation of their experimental seafloor. This method serves as a model for how "waves" can be used for non-intrusive imaging of objects. Examples - ultrasound, seismic mapping of the earth, radar imaging, NMR.

Graphs made using a motion detector can be used to study mapping of the topography of a model seafloor. A motion detector measures the distance to the nearest object in front of it by emitting and receiving pulses of ultrasound. A calculator can use distance and time measurements to produce a graph that represents surface features in much the same way that sonar does. In this experiment, you will use a TI Graphing Calculator, a CBL System, and a motion detector to produce graphs of seafloor.

In this experiment, students 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

    Grade Level/Discipline
    9 - 12 Physics and Earth Science

    National Standards

  • Content Standard A - Understandings about Scientific Inquiry - Scientists rely on technology to enhance the gathering and manipulation of data.

  • Content Standard C - Interaction of Energy and Matter - Waves, including sound and seismic waves, waves on water, and light waves have energy and can transfer energy when they interact with matter.

  • Content Standard E - Understanding About Science and Technology

    Pre-activity set-up
    This activity works best with students in groups of 3 or less. For a class of 24 students, 12 CBL's, calculators and motion detectors are ideal. (CBL units cost $179.00, and calculators are approximately $90.00. The motion detector is $65.00. All are available through Vernier Software Company and many other science supply companies.) Make sure that the calculators and CBL's have fresh batteries. The batteries last for weeks or months with heavy use if the students are prudent at turning them off after use.

    You will need to have access to a computer (Mac or Windows) with a TI-Graphlink cable. This device connects to the communication port on your computer and allows you to add programs to the calculator for students to collect data with. The Graphlink program for the computer is supplied with the cable (Graphlink price = $55.00). Updates to the Graphlink program are available at the Texas Instruments Website (http://www.ti.com/calc/docs/downloads.htm)

    The program PHYSCI will also have to be loaded onto each computer using the Graphlink and software. This program is also supplied with the Graphlink. Updates of the program are available at the same website. The program is also available at http://www.vernier.com/cbl/programs.html.

    Plan on taking about 1 minute per calculator to load the program. You can also do just one from the computer and have the students use a link cable between calculators to transfer the program one to one. This is a preference that will be based on the background of your students.

    Once the programs are on the calculator plan on about 5 to 10 minutes to test one of the units. Run through the program so that you are familiar with the program commands. The PHYSCI program is well written and will allow your students to do many other types of data collection as well as this activity. Occasionally students will get confused with selecting probes and picking the graph. If you read student procedure while checking through the program, you will recognize many of the potential problems your students might have.

    You will have to collect about 5 objects per group. Boxes, cans, etc are suggested, but you can use anything you have in your classroom for your students to use. It is also possible to image a person sitting or laying down with the motion detector as well. The only limitation to working with the motion detector is that you must have the detector a minimum of 0.5 meters above any object. If the distance is smaller than this then your data will be noisy.

    *** The graphs that the students generate on their calculators will be upside down relative to the objects. This occurs because the graph produced is Distance versus Time. The taller the object, the closer that it is to the motion detector. You can remedy this in one of two ways. 1. Simply explain to the students the idiosyncrasy of this graphing method and have them transpose their graphs 180 degrees when they draw them in their reports. 2. Have the students come up with a mathematical solution to get the data in the correct orientation. Both methods work well with the data. Choose which method works best for your class.

    This activity can be conducted in two parts. The first part is student driven. It will give them an opportunity to test their problem solving and analysis skills. If you choose to do the final part of the activity you will need to prepare an "unknown seafloor". At the end of the student procedure, they are told that they need to check with the teacher to complete the activity. You will have to construct a "seafloor" just as the students had, but yours should be placed behind a screen of cardboard or a sheet draped over some ring stands. Students will use the motion detector just as they did during the first part of the activity, but the only way that they can "see" your seafloor is through their data.


  • CBL System (you will need 1 per group of two. Three students maximum)
  • 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)

    Time Frame
    With introduction, prelab, lab and postlab, this activity works very well as a 3-day lesson with 50-minute class periods. This gives you and your students 1 full period to explore the science background and to become familiar with the setup of the activity and the idesyncracies of the equipment. One day is solely for data collection and analysis. The third day may be considered optional, but is an excellent opportunity to discuss the theory of this method of imaging as well as to reinforce the process of science and data collection.

    Engagement and Exploration (Student Inquiry Activity
    Initiate the activity by introducing the students to Antarctic Marine Geophysics by having them read individually or as a group journal entries at the TEA website. Suggested reading is at the journals written by Steven Stevenoski at http://www.wctc.net/~ssteven/antarc or ../../tea_stevenoskifrontpage.html

    Discuss - What factors affect collecting sonar data? - Does the motion of the ship have any affect on the data? - How far can sonar pulses travel? A crewmember received an interesting email message while we were in the Bransfield Straight. A friend aboard a Navy submarine in transit sent a message that stated that our active sonar was so loud it was driving them crazy. They were many miles away from the ship. They never gave a precise position - Why it is important to know what's below the ice or the sea?

    Do some hands-on modeling of the reflection of waves (Slinkies, etc.) A quick introduction to the fundamentals of sonar is a classic activity/demonstration where students measure the time for an echo. Have students measure a distance of about 50 meters away from a large solid two story or higher wall. Use a couple of boards slapped together to produce a loud sound wave. Have students record the length of time it takes from the moment the sound is made to the time that they hear the returned echo. Sonar works by measuring the echo time. This gives you an opportunity to discuss the importance of knowing temperature and density medium, because these affect the speed at which sound travels. (Distance = speed of sound x echo time/2)

    When doing Antarctic research, the temperature and salt concentration are constantly measured. The water actually increases in temperature with depth. To measure distances under these conditions you have to use an average of temperature to make your measurements. Another problem about working in Antarctica is that the sound waves travel in all directions. Sound reflected from sea ice and icebergs creates noise that must be removed either manually or electronically to an accurate view of the seafloor can be made.

    It is important that when you set up the hidden surface, have a parcticular feature those students need to find. This gives you an opportunity to assess their data interpretation skills and is a good practical evaluation tool.

    Explanation (Discussing)
    Discussion of what happened in the engagement and exploration section and why. Teacher acts as a facilitator for student discussion. Teacher also uses this time to assess student understanding and possible misconceptions. Introduce scientific terms and background as needed. Introduce polar research connections.

    Elaboration (Polar Applications)
    Present to your students the following ideas for discussion.

    Ask students how they think researchers know what type of topography is hidden by ice or water. Students might suggest the following:

  • They drill holes in the ice.
  • They send divers down to make maps.
  • They use submarines.
  • Etc…

    Explain that researchers can use sound waves to explore hidden surfaces. Ask students how they think this is possible. Students may know that bats and dolphins use echolocation to figure out where they are. If they mention this, ask them to explain how echolocation works. Students should be able to say that these animals send out sound waves and these waves bounce off of objects and travel back to the animals.

    Exchange (Students Draw Conclusions)

    Evaluation (Assessing Student Performance)


    Level 1

    Level 2

    Level 3

    Setup and Report Design

    Teacher assisted. Group needs step by step help to complete.

    Report and activity setup with minor support and encouragement from teacher.

    Setup and report is done within group. Teacher interaction is for confirmation and clarification.

    Graphing and Analysis

    Graphs have been made. Analysis is incomplete or incorrect.

    Graphs are complete and properly labeled. Analysis is mostly correct with minor errors.

    Graphs and analysis are thorough, complete and correct.

    Activity Report

    Parts of the report are missing, poorly labeled, lack organization.

    All components present, organization needs improvement.

    All components present, well organized, neat, spelling and grammar also correct.

    Unknown Seafloor

    Student has collected data, but has not completed graphs or interpreted data.

    Data has been collected and preliminary graphs are prepared without interpretation.

    Data and graphs are complete and well organized. Students are able to identify unknown objects from their data and graphs.

    data | hook | main | background & resources | student