MARS: Passive Acoustic Monitoring (Hydrophone)
- John Ryan
Monterey Bay Aquarium Research Institute
- George Matsumoto
Monterey Bay Aquarium Research Institute
Because acoustic information spans a tremendous range of frequencies, we must listen across a very broad spectrum. Capturing information at the high-frequency end of this range requires that we sample sound very frequently (more than 250,000 times each second). This frequent sampling of sound across a broad spectrum generates a tremendous flow of data. Isolated acoustic recording systems that rely on battery power and internal data storage must limit their deployment duration and the degree to which they can listen full-time. These constraints are removed by the MARS cabled observatory, which supplies power from shore and high-speed communication to data storage on shore, thereby enabling full-time recording for extended periods.
On July 28, 2015, a digital broadband hydrophone was connected to the MARS cabled observatory. Deployment went smoothly thanks to the ship’s crew and ROV pilots. Shortly after the sound of the ROV faded from the MARS node, as the ROV went back to the ship, marine mammal vocalizations became clearly audible on the hydrophone recordings. To see an example of a recording, click on the "Figures and Images" tab above.
This little hydrophone generates big data, about three gigabytes per hour. Understanding this voluminous and dense data requires a variety of analysis methods – from long-term views of variation in sound to very short-term occurrences of individual sounds. We are using daily summaries to provide a standard view of the soundscape. Producing a snapshot each day (Figure 2) we can examine daily patterns and their changes over longer periods (e.g. seasonal). This will in turn direct focused analysis toward time periods of particular interest. We are also developing software to automatically detect and classify marine mammal vocalizations using ‘machine learning’ methods. This requires training the automated algorithms using example recordings of the vocalizations that are of particular interest.
Summary to DateTo see spectrograms of the data collected, click here.
Historically, when oceanographers have placed instruments in the ocean, these instruments have either been attached to ships or have been powered by batteries. The first scenario only allows scientists to make measurements over relatively short time periods (typically days to weeks), while the ship is at sea. The second scenario allows instruments to be deployed for longer periods of time (typically months), but does not provide any way for researchers to know whether their instruments are working properly or to control them while experiments are underway.
The MARS observatory (and other cabled ocean observatories) provide oceanographic instruments with a full-time power and data connection to shore. Such observatories allow instruments to operate indefinitely, and to perform more power-hungry measurements than would be possible under battery power.
The high-speed data connection provide by the MARS observatory allows researchers to receive large amounts of data (for example, digital video streams) from their instruments in real time. It also allows researchers to control and assess the functionality of their instruments in real time. Researchers can receive data and control their instruments from anywhere in the world, through the internet.
The MARS ocean observatory has several purposes. It's primary purpose is to provide an easily accessible, deep-water facility where researchers can test equipment and instruments that may subsequently be deployed as part of the United States Ocean Observing Initiative (OOI). It also provides a site for researchers to test ocean observing equipment that may be deployed at other sites around the world. Finally, the MARS observatory provides an opportunity for researchers to perform experiments and collect unique physical, biological, geological, and chemical data on the marine environment in the vicinity of the MARS site.
What is MARS?
The Monterey Accelerated Research System (MARS) consists of a 52-km (32-mile) undersea cable that carries data and power to a "science node" on the deep seafloor. Science experiments can be attached to the science node using underwater data/power connectors and extension cords up to four kilometers long. The MARS science node is located on the seafloor at a depth of 891 meters (2,923 feet) below the ocean surface, on Smooth Ridge, about 25 kilometers west-northwest of Monterey.
The MARS science node has two titanium pressure housings. One housing contains electronic equipment that converts the 10,000 volts traveling from the shore cable to 375 volts (DC) used by science instruments. The second housing contains electronics that route data and control power to eight science ports. Experiments attached to each port can send up to 100 megabits per second of data through the science node and back to scientists' computers on shore.
DiscussionBelow are examples of sounds collected by the passive acoustic array. These are MP3 files and some versions of web browsers will not be able to play these files.
Humpback Whale (17 sec)
Blue Whale (21 sec)
Fin Whale (12sec)
Pacific White-Sided Dolphin (33 sec)
Marine Mammal Community (25 sec)
Cachalot (Sperm Whale) (25 sec)
Figures and Images
Figure 1. Fin whale vocalization as detected and recorded by the passive acoustic hydrophone attached to the MARS cable node maintained by MBARI.
Figure 2. Dr. John Ryan of MBARI plays the marine soundscape for an interested audience.