Biosonar-inspired signal processing and acoustic imaging from echolocating bats

Abstract

No biological system more immediately evokes thinking about technology than the sonar sense of bats [1,2]. This chapter describes a novel approach to sonar signal processing that has been identified from experiments carried out with echolocating bats. Bats use their biosonar to perceive target distance (range), target azimuth (crossrange), and target shape using wideband signals, and target velocity and fluttering motion using narrowband signals [2-4]. Being able to perceive these components in real-time while flying through surroundings that vary from simple to complex makes them a very valuable source of engineering inspiration. From a technological perspective, the parallels between biosonar and pulse-echo sensing by man-made radar and sonar systems are very compelling [5]. Moreover, progress towards understanding biosonar has benefitted from applying radar and sonar concepts to biology [5-8]. Furthermore, the historical development of radar and sonar technology overlapped with the discovery and advancement of research on biosonar [1,2,9,10]. Broadcast transmission, echo reception, signal-processing, display of images, and guidance of motion are recognizable functions both in biosonar [2,5] and man-made systems [9,10]. These functions correspond fairly well to specific stages in a block diagram of an engineered system. In biosonar, however, these functions are spread across several stages of biological and perceptual processing because they are interrelated and are carried out in a distributed fashion by overlapping biological structures [2]. The content of this chapter follows a signal-processing theme across stages in the bat's auditory system that comprises its sonar imaging system. At several stages in this story, operations seem similar to practices used in some man-made systems, only to have their outputs treated quite differently at higher stages.