When multiple active sonars, such as dolphins, bats, or mobile robots, interrogate the environment simultaneously, one view is that each sonar considers the signals produced by the others to be interference, while another view is that these signals contain useful information. A listening sonar can typically detect the time delay between another sonar’s interrogation emission and its corresponding echo from an object and possibly also the emission and echo directions. This letter first shows that, even if the directions of these two signals and relative delays are known, determining the object location is an ill-posed problem, supporting the interference view. It then shows the time delay alone provides useful information, indicating that no echo-producing object can be closer than a perceived minimum range. Echoes from specular surfaces provide similar information but also require self echolocation to refine the range estimate. Experimental acoustic waveforms illustrate the approach. The results indicate that traveling in fixed formation and emitting identifiable echolocation sounds faciliate cooperative echolocation by biological sonars.

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