Dolphin Echolocation Could Advance Medical Ultrasound

Increasing our understanding of the dolphin echolocation and communication signals could pave the way for sharper image quality on ultrasound technology.

Researchers at the Lund University (Sweden) department of biomedical engineering built a measuring instrument composed of 47 hydrophones capable of capturing a complete cross-section of dolphin sonar beams transmitted over many different frequencies. Dolphin sounds were then recorded in Kolmården Wildlife Park (Sweden) and in other wildlife parks located in the Bahamas, Honduras, and California (USA). The recordings revealed that dolphins actually emit two intertwined ultrasound beam components at different frequencies, and with slightly different timing.

Calculations revealed that the sound frequency is higher further up in the beam, producing a lighter echo within that area. According to the researchers, the slightly time separated signal components may enable the dolphin to quickly gauge the speed of approaching or fleeing prey, as variations in frequency provide more precise information on the position of an object. Working with researchers at the Lund Centre for Mathematical Sciences, they then developed a mathematical algorithm to disentangle and read the overlapping signals.

The algorithm effectively identified closely located Gaussian shaped transient pulses, even in heavy disruptive noise, automatically detecting and counting the number of transients, and giving the center times and center frequencies of all components. The researchers claim that the algorithm can increase understanding of dolphin communication, drive improvement is sonar devices and echosounders, and could also potentially be used to measure the thickness of organ membranes deep inside the human body. The study was published on May 22, 2018, in The Journal of the Acoustical Society of America.

“High and low frequencies are useful for different things. Sounds with low frequencies spread further under water, whereas sounds with high frequencies can provide more detailed information on the shape of the object,” said senior author Josefin Starkhammar, PhD. “It works almost like a magic formula! Suddenly we can see things that remained hidden with traditional methods. We could copy the principle of using sound beams whose frequency content changes over the cross-section.”

Echolocation is a biological ability to locate objects through sound waves. As Dolphins lack vocal cords, they produce sounds from the nasal air sacs, the blowhole, the larynx, the lungs, and the melon, an organ located in the upper inner area of the head filled with low-density lipids. For echolocation, dolphins emit ultrasounds called “clicks” in the nasal passages. The melon then groups the sounds into beams and amplifies the resonance. Sound waves bounce back from objects in the water to the lower jaw, with the teeth of dolphins work like antennas to receive the signals. The intensity, pitch, and time that it takes the echo to return to the dolphin provide information about the target.

Related Links:
Lund University