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Many existing tracking methods rely on post-processing or computationally intensive techniques, limiting their applicability to embedded devices. To overcome these limitations, we present a time-difference-of-arrival-based tracking algorithm that tracks multiple sources in the direction-of-arrival (DOA) domain. A key architectural feature of the method is the decoupling of continuous per-frame DOA estimation from source enumeration, enabling these processes to execute on parallel threads and ensuring that source enumeration does not degrade real-time throughput. We implement the algorithm in an open-source c++ software package, freewilli: Free software for Whale Identification and Localization with Low-Power Implementation. We demonstrate its effectiveness on passive acoustic recordings of diving beaked whale groups from a small volumetric four-channel hydrophone array deployment and show through a systematic parameter sweep that real-time processing latency remains stable across a wide range of detection rates and clustering configurations. The system operates at low power consumption (&amp;lt;1.3\u2009W) on a Raspberry Pi Zero 2\u2009W, enabling long-duration autonomous deployments.<\/jats:p>","DOI":"10.1121\/10.0044563","type":"journal-article","created":{"date-parts":[[2026,9,21]],"date-time":"2026-09-21T12:05:09Z","timestamp":1789992309000},"page":"2394-2405","update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Open-source real-time passive acoustic tracking of beaked whales for low-power devices"],"prefix":"10.1121","volume":"160","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2956-3002","authenticated-orcid":false,"given":"Joseph L.","family":"Walker","sequence":"first","affiliation":[{"name":"Department of Electrical and Computer Engineering, University of California San Diego 1 , San Diego, California 92093-0238,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zheng","family":"Zeng","sequence":"additional","affiliation":[{"name":"Scripps Institution of Oceanography, University of California San Diego 2 , San Diego, California 92093-0238,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"William A.","family":"Deans","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, University of California San Diego 1 , San Diego, California 92093-0238,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lauren M.","family":"Baggett","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, University of California San Diego 1 , San Diego, California 92093-0238,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9686-035X","authenticated-orcid":false,"given":"Sean M.","family":"Wiggins","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, University of California San Diego 1 , San Diego, California 92093-0238,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bruce J.","family":"Thayre","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, University of California San Diego 1 , San Diego, California 92093-0238,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2401-8569","authenticated-orcid":false,"given":"Kaitlin E.","family":"Frasier","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, University of California San Diego 1 , San Diego, California 92093-0238,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"231","published-online":{"date-parts":[[2026,9,21]]},"reference":[{"key":"2026092108040854200_c1","volume-title":"Principles of Marine Bioacoustics","year":"2008"},{"key":"2026092108040854200_c2","doi-asserted-by":"publisher","first-page":"239","DOI":"10.1016\/j.ins.2014.04.055","article-title":"A joint possibilistic data association technique for tracking multiple targets in a cluttered environment","volume":"280","year":"2014","journal-title":"Inf. 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