Special section on biologically-inspired radar and sonar systems - Why dolphin biosonar performs so well in spite of mediocre ´equipment´

Dolphins have been found to have an excellent sonar system that is able to detect and recognise targets in noisy and highly reverberant environments. However, their `equipment` has only mediocre characteristics from a technological sonar perspective. How dolphins perform the biosonar task so well is addressed in this manuscript. Echolocating dolphins have the capability to make fine discrimination of target properties such as wall thickness difference of water-filled cylinders and material differences in metallic plates, and to discriminate and recognise species of fish food. The high temporal resolution of the biosonar signals along with the high dynamic range of its auditory system are critical factors for target discrimination. An experiment in metallic plate composition discrimination suggests that dolphins attended to echoes 20`30`dB below the maximum level. Some of the properties of the dolphin sonar system are fairly mediocre, yet the total performance of the system is often outstanding. When compared to some technological sonar, the energy content of the dolphin sonar signal is not very high, the transmission and receiving beamwidths are fairly large, and the auditory filters are not very narrow. Yet the dolphin sonar has demonstrated excellent capabilities in spite of some mediocre features of its `hardware`.