While dolphins are capable of shape recognition, it is unclear how they perform this task well given their limited sensory aperture. From a practical viewpoint, this helps evaluate techniques that may help enhance the performance of man-made sonar.

The aim is to determine what sonar performance we can obtain and what processing may be required to differentiate targets as effectively as the dolphin. We use this to insonify the same objects used in the EV-MTS trials and analyse the recordings. Furthermore, we develop a biomimetic-sonar system that mimics the dolphin’s biosonar by using (1) a broadband dolphin-like transmit signal, (2) emitted by high-frequency transmitters placed at different locations, and (3) multiple repeated clicks. This allows us to better observe the capabilities of dolphin echolocation using high-frequency recording equipment. In these experiments, the dolphin is able to perform certain target-discrimination tasks. In order to better understand the shape-recognition capabilities of dolphin biosonar with an aim to replicate it in a biomimetic system, we conduct EV-MTS experiments in a pool 8, 9, 10 (Fig. Moreover, the instrumentation required to record or transmit dolphin-like signals with high frequency and bandwidth has only been slowly evolving over the past decades 4. The dolphin brain and sonar are complex systems, which makes it hard to examine their individual aspects like shape-recognition, without isolating others such as behavioural biases. Obtaining a deeper understanding of how dolphins process echolocation information is challenging. This behaviour is demonstrated by echoic-to-visual (EV) cross-modal matching-to-sample (MTS) experiments, in which a dolphin uses echolocation to inspect a sample, and identify the match from amongst alternative objects through its visual sense 8. Behavioural studies demonstrate that dolphins can sense objects both visually and echoically, and transfer information across these sensory modes 6, 7. Dolphins can use their biosonar to identify objects varying in size, shape, and material 5. The biological sonar of dolphins surpasses any current man-made imaging sonars of similar size and frequency 2, 3, 4.

Biomimetic sonars that are inspired from marine mammals such as dolphins are an emerging development in this field 1.

Underwater imaging sonars are an essential technology for oceanic exploration and have been in use for many decades in several applications. Our findings offer insights and tools towards compact higher resolution sonar imaging technologies. We subsequently develop a biomimetic sonar system that combines sparsity-aware signal processing with high-frequency broadband click signals similar to that of dolphins, emitted by an array of transmitters. We find that infusing prior information into the processing, specifically the sparsity of the shapes, yields a clearer interpretation of the echoes than conventional signal processing.

We record the echoes the dolphin receives and are able to extract object shape information from these recordings. In order to gain better understanding of dolphin sonar imaging, we train a dolphin to acoustically interrogate certain objects and match them visually. The sonar system of dolphins, which uses sound pulses called clicks to investigate their environment, offers superior shape discrimination capability compared to human-derived imaging sonars of similar size and frequency. Underwater imaging sonars are widely used for oceanic exploration but are bulky and expensive for some applications.

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