The Development of RADAR and SONAR K. Lee Lerner scholar.harvard.edu/kleelerner kleelerner@alumni.harvard.edu This is a DRAFT COPY of an article subsequently published in the RUSA-award-winning Science and Its Times: Understanding the Social Significance of Scientific Discovery, edited by Neil Schlager and Josh Lauer, and published in eight volumes by Thomson Gale (now Cengage Gale) from 1999 to 2001. In 2018 Amazon added Science and Its Times to its "Best of History Books" collection. Overview Although they rely on two fundamentally different types of wave transmission, Radio Detection And Ranging (RADAR) and Sound Navigation and Ranging (SONAR) both are remote sensing systems with important military, scientific and commercial applications. RADAR sends out electromagnetic waves, active SONAR transmits acoustic (i.e., sound) waves. In both systems these waves return echoes from certain features or targets that allow the determination of important properties and attributes of the target (i.e., shape, size, speed, distance, etc.). Because electromagnetic waves are strongly attenuated (diminished) in water, RADAR signals are mostly used for ground or atmospheric observations. Because SONAR signals easily penetrate water, they are ideal for navigation and measurement under water Background For hundreds of years, non-mechanical underwater listening devices (listening tubes) had been used to detect sound in water. As early as 1882, a Swiss physicist Daviel Colladen attempted to calculate the speed of sound in the known depths of Lake Geneva