Hydrophone instruments include high frequency (10 to 200,000 Hz) and low frequency (0.1 to 1600 Hz) models. Hydrophones are acoustic instruments that can process data while they are being collected to produce calibrated waveform data. Hydrophones are typically used to study vocalizations of marine mammals, ship traffic and ambient noise.

Hydrophone data at sites like Folger Deep and Strait of Georgia are used to detect vocalizations, which are examined to study seasonal shifts in cetacean populations. Whale songs are detectable by hydrophones from tens to hundreds of kilometres away from the source. Species (such as orcas) and sub-populations (such as resident, transient or offshore orcas) are identified by their unique calls.