Advances in sonar technology have contributed to some remarkable rediscoveries of ships lost at sea, notably the Titanic and last month the space capsule, Liberty Bell (see Liberating the Liberty Bell), which sank in 1961 after the hatch blew off prematurely.

RMS Titanic, Inc.--the only entity legally entitled to recover objects from the Titanic--is a partner in a new research and recovery expedition. The Battleship Yamato Research and Recovery expedition got underway on August 15, 1999, in the East China Sea, approximately 250 miles north of Okinawa. You can follow the reports from the expedition.

The Battleship Yamato was designed in 1936, and remains the largest battleship ever built. Yamato left the naval harbor of Kure on April 6, 1945. The next day, the Yamato was engaged with the U.S. Naval Fleet and its extensive carrier support. Within two hours, the Yamato foundered and began to sink.

Learn about the Problem

The technology used for searching for vehicles on the ocean floor--at depths of three miles or more from sea level--has grown extremely sophisticated, enabling finds today that weren't possible only a few years ago. The underlying principle of the instruments used in the search and recovery expeditions is ultrasound, sound waves sent out to the ocean floor and then received after they bounce back off the floor. Today's instrumentation records the returned signals and then decodes and digitizes them to create a "picture" of the ocean floor.

Learn about the basics of ultrasound as used for visualizing the ocean floor and for examining in-utero fetuses in the Physics Explorer activity Ultrasound.

Think about the Problem

Once the ultrasound transmitter has received a return sound wave, it must be translated into an image, much like the eye translates light waves into images.

Ultrasound waves have a wavelength of several millimeters. How does wavelength affect the resolution of the image? For a more detailed image, should you use a shorter or a longer wavelength?

For the Teacher: Extending the Problem

• For students who want more information about the advanced technology and methods used in these expeditions, information is available at the following sites:
  • Liberating the Liberty Bell: The Search
  • Titanic: Raising a Legend: Engine Room
  • Nauticos (a company involved in the Titanic expedition): The projects section of this site is still under development, but the Still Photography sections of the different expeditions have some interesting photos, including actual sonograms of the ocean floor.
  • Students may also be interested in how technology is advancing other areas of archaeology: Space technology helps crack riddles of archaeology.
    
    
• One of the most common uses of ultrasound is in medicine. Some students may have personal experience with ultrasound exams. Below are some discussions of both medical and non-medical applications of ultrasound.
  • Harvard Medical School: Radiology: Ultrasound: This site gives a detailed explanation, geared to the patient, of different types of ultrasound exams. Students who would like to explore other types of medical imagery can find a list of kinds of exams.
  • Obstetric Ultrasound: Presents different ultrasound technologies and the purposes of ultrasound in obstetrics. Includes a gallery of images of the fetus and a doppler recording of a fetal heartbeat.
  • UltraSound Solutions: Although this is a commercial site of a company trying to sell ultrasound equipment, it presents a list of non-medical ultrasound applications that may interest students.
    
    
• Another major discovery of a ship at rest on the ocean floor is that of the Israeli submarine, Dakar, which disappeared in January 1968, while en route from England to Israel. The sub's buoy marker was found a year later off the coast of the Gaza Strip, which together with other evidence led experts to believe that the Dakar was 50-70 nautical miles off from her planned route. As a result, expeditions over the years searched the wrong area of the ocean floor in looking for the Dakar--the proverbial looking for the needle in the haystack. Have students read the story of the Dakar and discuss what sort of information the organizers of an expedition may need in order to choose the location of their search.
  
  
• Other sites of interest :
  • Nova Online: Titanic's Lost Sister: Based on a Nova TV broadcast, this site can be used as an independent interactive unit; includes a teacher's guide.
  • LaSalle Shipwreck Project: This site is dedicated to the excavation and conservation of the Belle, one of the earliest shipwrecks found in North America. The site includes extensive information and photos of the excavation, the conservation of artifacts, the historical setting of La Salle, and online issues of Journeys, a newsletter for educators full of activities and teaching ideas based on the project.
  • Sunken Slave Ship: How and what can we learn from a shipwreck?: A Newton's Apple lesson plan for an activity based on marine archaeology.