Hydrophone and Towed Arrays
       A hydrophone array consists of multiple hydrophones positioned in precise locations.  The hydrophones and associated pre-amplifier boards are encased in an acoustically transparent, oil-filled tube.  Arrays utilized by the Scripps Whale Acoustics Lab range from 100 – 300 meters in length and contain four to six individual hydrophones.  The hydrophones utilized in our arrays have a frequency range extending from 10 Hz – 200 kHz, which permits recordings from a wide range of marine mammal species.  Hydrophone arrays can either be towed behind a vessel for real-time, underway monitoring or fixed for stationary monitoring of a specific location.  Sound arriving at the array from a source, such as a vocalizing whale, will reach each hydrophone at slightly different times.  The time-of-arrival-differences can subsequently be used to calculate the bearing and distance to a calling animal. Hydrophone arrays are often used in association with visual observation techniques to allow for marine mammal calls to be correlated with information on species, gender and behavior.
Fixed arrays have been deployed from FLIP in three configurations:

1) vertical orientation allowing for omni-directional recordings of marine mammals;
2) horizontal orientation with the array suspended from a PVC frame 40 meters below     the surface;
3) billboard configuration with the array connected to a PVC frame such that three     hydrophones are suspended in the horizontal plane while two are positioned in the     vertical plane.

       On a typical FLIP deployment, all three array configurations are fixed in position to allow for long-term continuous acoustic monitoring of a study site.

Billboard array configuration (left)
Towed array animation (below)

Credit: Elizabeth Henderson and Greg Campbell