<P>Have you ever wondered how stealth planes achieve "invisibility," how sunken ships are found, or how fishermen track schools of fish in vast expanses of ocean? Radar and sonar echolocation—a simple matter of sending, receiving, and processing signals.</P><P>Weaving history with simple science, Mark Denny deftly reveals the world of radar and sonar to the curious reader, technology buff, and expert alike. He begins with an early history of the Chain Home radar system used during World War II and then provides accessible and engaging explanations of the physics that make signal processing possible. Basic diagrams and formulas show how electromagnetic and sound waves are transmitted, received, and converted into images, allowing you to literally see in the dark.</P><P>A section on bioacoustic echolocation, with a focus on the superior sonar systems of bats and whales and a discussion of the advanced technology of next-generation airborne signal processors, opens the imagination to fascinating possibilities for the future.</P>