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Harbour Porpoise Livestreaming

and the sound of Little Belt

Go below the surface with Aarhus University, Nature Park Little Belt and Seiche Ldt.


Activate the livestreame, click on the picture below:

Technical guide

Explaining the Livestream setup

The youtube window

Eavesdrop on the life of Harbour porpoises Little Belt livestreaming


1: A map of Little Belt just outside Middelfart city. This map is linked to the AIS system, so that every boat that uses this system will appear on the map as an arrow, noting direction. Not every boat uses this system, so you may see boats sailing by the webcam without an arrow showing the position on the map.

2: This graph shows recorded sounds occurring within the last minute. The red colour indicates sound that the program has categorized as porpoise clicks. The green colour show sounds that are similar to porpoise clicks, but cannot be categorized as such.

3: This graph shows recorded sounds occurring within the last hour. Occasionally you will see a lot of red activity without the presence of a porpoise. This is due to the fact that some engines produce noise in the same frequency as the porpoise clicks and these are registered as false positives.

4: This graph shows the repetition rate of the porpoise clicks. If the red dots follow each other in two equal rows, then the sound is likely from a ship engine, and the false positive from before can now be excluded.

5: The webcam is streaming live video from the dock site. The hydrophone is placed towards the left of the picture, close to the yellow buoy. The map in nr:1 is marked with red where the webcam is located. 

6: The spectrogram shows you recorded sound in kHz. Noise intensity is visualized using colour; with blacks/dark blues signifying little to no sound, greens, yellow, and oranges signifying intermediate sound amplitudes, and reds representing very strong amplitudes. The bottom of the spectrogram illustrates sound recorded at 1 kHz, rising up to 12 kHz at the top. 

A: The appearance of the sound waves B: Correlation between frequency and amplitude.: Map of Little Belt showing Middelfart city. Ships are shown with arrows and a green line, using the AIS systeme that all ships over 12 meters are required to use on board. Smaller boats can be seen on the webcam without showing on the map.

Beneath the surface

A story exists about the calm, blue sea, filled with a fascinating silence so intense that it makes you dream about floating alone in the deep blue, consumed by this almost meditative soundless world. The truth is that underneath the surface exists a complex collection of different noises created by millions of lives. These sounds contain a great amount of information about mating habits, navigation, and behaviour. Beside these natural sounds, the oceans are contaminated by the noise of humans. From before the age of the Vikings, humans have used the oceans as a road of transportation and a source of food, but in the last couple of hundred years, the intensity and sources of this exploitation have changed rapidly. The sounds that we are producing now come primarily from large vessels, transportation, wind farms, oil industries, construction, sonar and more. It is known that the noise we humans produce below the surface is interacting with the millions of lives that exist there. The anthropogenic noise can become so intense that it can cause organisms to leave important areas, by disrupting their socialising, navigating, and mating, or even physically harming them through boat interactions and collisions by boats. We know that the noise affects their lives and causes stress, but scientific research related to the effects of human noise on marine life is still relatively recent and findings are limited. It is a pleasure to welcome you all, to the first Danish underwater livestreaming audio station in Middelfart, in collaboration with Aarhus University and Seiche Limited. It is with great pleasure that we now have the opportunity to send you on a live audio tour below the surface of Lillebælt.

We recommend that you take a few minutes to tune in and listen for the electrical sound of the Danish porpoise (Phocoena phocoena) and the rest of this fascinating universe.


Porpoise frequency

Harbour porpoises uses their biosonar also known as echo sound, for navigation, communication and hunting. When they pass by the hydrophone, the sound is recorded and transferred by cable to the shore. In the wheelhouse a computer stores all the recordings and livestream the signal. Due to the fact that porpoises produce sound at a much higher frequency (130 kHz) than people can actually hear (0,02-20 kHz), the computer transform the signal down.

A ship produce sound at many different frequencies. Some of the sound is sonar that we cannot hear. Boat sonar is uset for navigation, and fish-finding. These sonar sounds are produced around the same frequency as the porpoise biosonar.

Audio Gallery

Discover the sounds of the sea:

Do you know the sound og porpoise sonar? or are you interested in listening to the noise of a speedboat or a vessel? Then listen to the recordings below.


The setup, the future and just trivial knowledge:

By putting a hydrophone down at the bottom of the Little belt, gives us direct access to the world of sounds underneath the surface.

Harbour porpoise

Porpoise sounds with a metal chain in the background.

Medium size boats

Sailboat running on engine

Fishing boat

The boat is visible after 1:45 minutter.

Large boat

Large boat and noise

High noise level! The recording is 10 min long.

Small boats


Distant boat

The Hydrophone

An underwater microphone

To monitor the porpoises, we are using cutting edge technology consisting of an underwater microphone, known as a hydrophone, which is mounted on a tripod in the middle of the estuary, at 15 meters depth and 180 meters from shore. The hydrophone is capable of recording sound far beyond the human hearing range, and is hardwired to an audio capture PC located in a small building on shore. The sound captured from the hydrophone is then manipulated in such a way that humans are able to both listen to the clicks and see a visual representation of the sound simultaneously at the same time. Furthermore, we also have setup a land-based webcam pointed towards the hydrophone. This allows us to gauge what ships are likely to produce what sounds. To do this we use a program called PAMGuard.

Illustration by Seiche Ldt. 

More technical information: Seiche.com

Harbour Porpoise - Phocoena phocoena

A broken silence

There is a continuous scratching sound of water rushing by the hydrophone. It is filled with particles and bubbles and floats through the speakers mixing with a distant clink of the buoy chain. This noisy silence is suddenly interrupted by an unforgettable and almost unreal electrical snore that sounds more like electrical impulses, an underwater bat, or a crazy Kazoo, than what it actually is. This sound is coming from the smallest whale in Denmark, the harbour porpoise.


This electrical click sound is the echolocation and sonar of the harbour porpoise, two terms describing porpoise communication, foraging and navigation. It begins with small pulses of sound, sent out through the water hopefully hitting a fish or the seabed and thereby reflecting the sound back towards the whale as an echo. With these echo clicks, the porpoise can navigate through obstacles and find food, even at night. The frequency and intensity of these clicks vary, and through continuously observations this electrical dub event, scientists are able to reveal the behaviour of the porpoises.

Read more about:

Harbour porpoises

Acoustic monitoring

Ship noise

Video Gallery

Join the divers below the surface:

Diving to the hydrophone Visiting the hydrophone after 6 months, movie by Florian Graner @sealife-production
Below the surface A short video produced by Ocean adventures, Middelfart


Links and further information: