Passive Acoustic Monitoring: Listening for marine life

Passive Acoustic Monitoring (PAM) in this context basically means making audio recordings underwater, preferably:

  • year-round, if not for several years

  • 24/7, night and day

  • covering the highest frequencies possible  

  • and the full dynamic range from silence to the loudest signals

As one can imagine, running a tape recorder continuously for years in a row is energetically quite demanding, even more so, when you would like to do so in a remote ocean during long periods of darkness during wintertime.  Fortunately, the invention and progress in digital recording and storage, now allows to acquire battery powered autonomous passive acoustic recorders which can continuously collect high-end underwater recordings for long periods.

We use such recorders in two different ways:

  • buried, since 2006,  in the floating shelf ice with a hydrophone dangling from the bottom of the ice shelf, baptized PALAOA (Perennial Acoustic Observatory in the Antarctic Ocean, or “whale” in Hawaiian.

  • attached, since 2008, to deep-sea mooring of the oceanographic Hybrid Antarctic Float Observatory (HAFOS) and the Frontiers in Arctic Marine Science (FRAM) observatory, which are distributed across the Weddell Sea and Fram Strait, respectively.

See the maps to the right for of the recording sites occupied so far.  Please note that not all sites are equipped with recorders at all time.

Maps of the Arctic and Antarctic with underwater sound recording sites occupied by the AWI Ocean Acoustics group since 2006.

PALAOA  (PerenniAL Acoustic Observatory in the Antarctic Ocean)

Between 2006 and 2014, PALAOA recorded underwater sounds and broadcasted live via the internet. Power for data acquisition and interruption free  wireless data transmission from PALAOA to the Neumayer station was generated locally by an alternative energy solution (batteries, solar, wind and fuel cell), even throughout the darkness of the polar winter.  Data was collected by two hydrophones using lab-type digitizing and encoding equipment.  Data was recorded year-round, 24/7, mostly at 48 kHz sampling rate with 16-bit depth, saving 1-minute long mp3-compressed files, which were streamed to the internet.

However, with this solution being highly labor intensive, we had to switch to a less demanding offline data acquisition system.  Since December 2014, PALAOA consists of a simple aluminum box containing two 12V AGM rechargable batteries and an acoustic recording unit like the ones used by the PAM recorders in HAFOS.  This takes advantage of the recorder now sitting just under the icy surface of the ice shelf, accessible by the Neumayer overwintering team for battery replacement and data retrieval every few months. PALAOA now records year-round, 24/7, at a 96000 Hz sampling rate with 24-bit depth, saving wav files of 10-min lengths.


The old PALAOA station (2006 - 2014)

Setting up the "new" PALAOA (2014 ff) in an aluminum box lowered into a trench dug into the snow, to be covered by a wooden particle board and about a foot of snow for protection against cold weather. 

HAFOS  (Hybrid Antarctic Float Observing System)

A HAFOS deep-sea mooring consists of a long rope, up to several thousand meters, extending from the sea floor, where it is attached to an anchor weight, to some 200m below the sea surface, where it is attached to floatation elements that keep it upright throughout the water column.  Distributed along this rope one or more acoustic recorders are attached, along with other oceanographic instrumentation.  Moorings are deployed by ship – primarily our beloved RV Polarstern – and recovered 2-3 years later.  Only then we are able to download the data and learn what surprises might be buried therein.  Early recorders covered up to 11 months at 5553 Hz, 24-bit depth, while latest versions covered up to 24 months at 24000 Hz, the improvement mostly being due to increases in available SD card memory size.

Schematic of a HAFOS deep sea mooring.  Mooring elements, top to bottom: floatation at 200m depth, Aural acoustic recorder at 210m depth, SonoVault acoustic recorder at 212m depth, acoustic current profiler at 314m depth, salinity and temperature logger at 316m depth, two acoustic releases side-by-side at 317m depth, i.e. 2m above the sea floor, and the anchor (old railroad wheels).

FRAM  (Frontiers in Arctic Marine Science)

The AWIs FRAM moorings also host a set of underwater recorders in the northern Greenland Sea. Together with so called AZFPs ( Acoustic Zooplankton and Fish Profiler) the monitor for whales, seals, fish and invertebrates between Spitsbergen and Greenland. Further moorings in the adjacent Arctic Ocean extend this array slightly to the North.

MAP of FRAM moorings hosting PAM recorders an AZFPs.  Please note, that not all locations were occupied at all times.

Dedicated field studies

Over the years we also conducted some dedicated field studies, limited in scope and duration, to address specific questions like ....

2019  eDNA-PAM pilot Port Elizabeth, ZA

Pilot study by HIFMB-AWI off Port Elizabeth (South Africa) during which passive acoustic records and water samples for eDNA were simultaneously collected, this approach will allow direct comparison of species detections between both methods.

2016 - 2019  North Sea Pilot

Pilot study in collaboration with BioConsult Holstein. Deployment of an IcLIsten Recorder in the German North Sea,  southwest of the Doggerbank from October 2016 - March 2019.

2015 & 2016 SAMBAY: San Antonio Model BAY for passive acoustic density estimation, ARG

As a a collaborative project between the OZA and the MaryBio Research Foundation in Patagonia, Argentina, SAMBAY analysed southern right whale behavior and acoustic propagation properties to estimate animal density from passive acoustic monitoring.

2014/15 Acoustic mensuration of RV Polarstern during expedition PS89

To capture the sound field of RV Polarstern as experienced by a marine mammal close to the sea surface we recorded the ship's passage on two occasions with hydrophones dipped to 10m depth from a free drifting zodiac while RV Polarstern passed by at 10kns  (Closest Point of Approach, CPA ca. 180m)

2013 Acoustic mensuration of cargo ship Nadezhda

To capture the sound emission of a fully powered POD drive, we conducted an acoustic mensuration of cargo ship Nadezhda while steaming.  Recordings were taken using a bottom mounted icListen hydrophone and Reson TC4032 lowered from pilot vessel Döse.

2012/13 PASATA (PASsive Acoustic Tracking of Antarctic marine mammals)

The aim of the PASATA project was to use time-synchronized passive acoustic recorders to localize vocalizing marine mammals in the Atka Bay area. Alongside the passive acoustic recordings, on-ice and underwater camera systems were deployed near Weddell seal breathing holes as a pilot project to obtain additional visual information on this species' behavioural activity.

2010/11 Polarstern expedition ANT-XXVII/2

Field Recordings at Rothera

2009 Polarstern expedition ANT-XXV/2

Deployment of 6 GPS tracked PALAOA-S recorders near Maud Rise.  RESON TC4032 hydrophone connected to an M-Audio recorder. with solar panel.

2008 Polarstern expedition ANT-XXIV/3

Deployment of 2 PALAOA-S recorders in Atka Bay.  RESON TC4032 hydrophone connected to an M-Audio recorder in Zarges box.

2006 Polarstern expedition ANT-XXIII/6   doi:10.2312/BzPM_0580_2008

Test of a passive acoustic streamer towed behind Polarstern, sea ice based PAM for leopard seals for diver safety in the vicinity of Polarstern, and PAM recordings at a separate site 60nm from Polarstern for 12h at 192 kHz.

2005 Polarstern expedition ANT-XXII/3

Test of a passive acoustic streamer towed behind Polarstern, deployment of 10 sonobuoys, deployment of 3 PODs in the Weddell Sea.

2003 Polarstern expedition ARK XIX/4

Stationary acoustic mensuration of RV Polarstern and its hydroacoustic equipment at the Heggerness acoustic range in the Herdle Fjord, Norway.  Acoustic measurements were conducted by the Wehrtechnische Dienststelle WTD71, who operated the range together with its European partners.

2002/3 Polarstern expedition ANT-XX/2

First trials of underwater recordings in Atka Bay.

PALAOA Satellite Recorders  (to be completed)

A SonoVault recorder is being deployed on a deep-sea mooring.

PALAOA recording electronics and power supply for the active hydrophone within the aluminum box.

Setting up a PASATA recorder near a group of Weddell seals on the sea ice of Atka bay, Antarcitca.