Rockhopper – Marine Passive Acoustic Recording Unit

Following the footprints of its predecessor, Rockhopper acoustic recording units were developed to enable scientists to study any acoustically active marine species of interest. Due to its origin at the Cornell Lab of Ornithology, the recording instrument was named after one of our favorite marine birds – the Rockhopper Penguin. Rockhopper’s predecessor, MARUs (Marine Autonomous Recording Units), had been in operation for almost two decades. MARUs were designed to record baleen whale species that are known to use low frequency acoustic signals. Thus, MARUs were designed for recording at low sampling rates, which provided an advantage in energy budget and data storage capacity for long duration continuous data collection.

Two major improvement needs guided the development of the Rockhopper platform. The first desired improvement was to increase the capability of the unit to record at a significantly higher sampling rate compared to the MARU platform. Aquatic organisms are known to produce acoustic signals within a wide frequency range. The limits of the sampling rate of a recording instrument restricts which vocalizations can be recorded with a particular device. To capture the higher frequency elements of marine soundscape, a recording unit needs to be equipped with instruments capable of recording at a high sampling rate. The Rockhopper can sample at 394 kHz (4X higher than the MARUs), allowing the units to record sounds of most marine species.

The second desired improvement was audio quality. Rockhopper was made to achieve a very low noise floor, particularly at frequencies below 10 kHz. Noise floor is associated with the self-noise generated by the instruments inside the unit. A low noise floor allows more accurate representation of ambient noise or species signal information without the influence of the noise generated by the unit. A low noise floor allows the units to record better quality animal signals, anthropogenic (man-made) noise, and other ambient noise present in the environment.

CCB team deployed the first Rockhoppers unit in the Gulf of Mexico in May 2018. Subsequently, more Rockhopper units were deployed in the Gulf of Mexico for research purposes. Form factor is a major advantage of Rockhopper units compared to other commercially available marine recording units. The units are small enough to be deployed by a single individual using a small vessel, which provides flexibility in field operation, cost savings, and efficiency in deployment/recovery process. If you are interested in these units or have additional questions, please contact us.