Project Bhulan

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Problem

A dolphin found dead. (Source: Animal Discovery)

The Indus River dolphins (Platanista gangetica minor ) – one of the few river dolphins in the world – inhabit a long stretch of the Indus River. Six barrages (Jinnah, Chashma, Taunsa, Guddu, Sukkur and Kotri) built on the river, fragment the dolphin population into five sub-populations. However, the highest population of the dolphins resides between Guddu (28.4 N, 69.7 E) and Sukkur (27.7 N, 68.9 E) (Braulik, 2006). Over the last few decades, a rapid decline in their population has brought them on the verge of extinction, most probably because dolphins wander into the irrigation canals during high flood season, but in winter, (when the canals are closed for cleanup) they get trapped in small desiccating pools and die because of inaccessibility to food. Due to such a decline in their population, International Union for Conservation of Nature (IUCN) has labeled them as an endangered species (Braulik et al., 2004). Several organizations, specially WWF Pakistan, are working to conserve this species. For their conservation, we need to develop a robust and reliable system for tracking and analyzing the activities of these dolphins, so that the stranded dolphins can be timely rescued, and any other reasons for the decline in their population can be determined.

A dolphin rescue operation by WWF Pakistan.

Approach

Lacking a functional eyesight, the Indus River dolphins perceive their environment through echolocation (the use of sound waves to detect objects). To achieve this, they produce sound waves in the form of trains of pulses (or clicks) – click trains – ranging from 15kHz to 250kHz in frequency, and sense the reflections back. We can sense these clicks through underwater-sound-sensing devices, called hydrophones. These clicks are then extracted from the stream of incoming sensory data using an appropriate algorithm. To localize a dolphin in 3D space ( $x,~y,~z$ coordinates), an array of at least five hydrophones should be used. The array must have an appropriate geometry to enable complete 3D localization. One of the hydrophones can be set as reference, and the time-delays in signal reception between this reference hydrophone and the rest of the four hydrophones can be used to localize a dolphin; using the same technique that is used for multilateration.