Shipwrecks may lie several kilometers deep at the bottom of the ocean. Sometimes air crashes occur over water, and the wreckage sinks to the bottom of the sea. Often it is necessary to find these wrecks, either to recover valuable cargo or to find out the cause of the disaster.
Wrecks usually lie so deep that divers and submarines cannot reach them. They are located by ‘sonar’. Sonar equipment transmits sound waves through water. The waves bounce off objects on the seabed. A receiver picks up these reflected waves and producers a picture of the seabed on which wrecks or other foreign objects stand out.
Sometimes exploring parties send a ‘submersible’ to the bottom of the sea. It is an underwater craft equipped with lights, television cameras and claws to grip objects. The submersible is controlled by the crew on the ship above.
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