Sonar (originally an acronym for Sound Navigation And Ranging) is a technique that uses sound propagation to navigate, communicate with or detect other vessels. Sonar may be used for the measurement of the echo characteristics of "objects" in the water. Sonar may also be used in air for robot navigation, and SODAR (an upward looking in-air sonar) is used for atmospheric investigations. In addition to its well understood military applications of detecting and tracking enemy ships & submarines and mine avoidance, SONAR is widely used in fisheries, echo sounding, net location, vehicle location and medical applications such as sonography and prosthesis for the visually impaired. In the context of this quiz, the figures “Number of Questions In Actual Exam”, “Time Allowed In Actual Exam” and “Passing Percentage” are just arbitrary values.