Underwater audio and video, Sardinia. 2006
In 2006, we were asked to design and propose an integrated audio/video system capable of carrying out activities that would be impossible for scientists to perform using standard methods.
The first task was the audio/video monitoring of two partially submerged caves. Both sites are remote and difficult to access, either by land or by sea. This type of surveillance had a scientific purpose.
The second task involved planning an underwater acoustic monitoring activity in the Marine Protected Area, with the goal of gathering information on the noise levels present in the zone.
The third task was focused on collecting data on “sea usage.” The area managers were interested in understanding the habits of commercial operators (mainly diving centers and small-scale fisheries) active within the area.
The area
The site is located in the far southeast of Sardinia. It is a sandy coastline interspersed with large and frequent granite formations. Sparsely inhabited, it is a rather wild and evocative area, sustained mainly by seasonal tourism.
Communication infrastructure is limited (cell network coverage is weak outside the village).
The seabed is sandy and ranges from 0 to -250 meters in depth.
A Marine Protected Area is present, well established and regulated with special provisions.
The area is rich in biodiversity, with frequent sightings of cetaceans and turtles.
Preliminary studies
A standard survey was conducted before any feasibility study. Digital mapping data was acquired.
Implementation
Le grotteThe caves
After several tests, we decided to propose the installation of two special video cameras inside the caves, connected to a base station via a long-distance wireless Ethernet link.
The video signal is digitized through a video server and transmitted over the network.
Both sites are connected to a third node, located on a small island: the lighthouse, visible from one of the monitored caves.
To reach the lighthouse from the sites, it was necessary to set up a signal bounce network. From there, the video stream is forwarded to the municipal office, where it can be received and, if necessary, recorded.
The lighthouse as seen from one of the monitored caves.
The lighthouse and the network
At the island’s lighthouse, an essential part of the equipment was installed:
two motorized PTZ cameras
the relay for the wireless Ethernet link
the underwater acoustic monitoring system
The entire setup is energetically autonomous, powered by a small wind turbine and a set of photovoltaic panels.
The acoustic monitoring is based on a wired analog hydrophone, positioned about 800 meters from the lighthouse, at a seabed depth of 28 meters.
The signal is acquired and managed locally for analysis and storage.
Acoustic monitoring
The hydrophone signal is acquired through an analog-to-digital (AD) converter and stored on a low-power computer installed at the lighthouse.
This computer is connected to the central station (located at the municipal office) via the Hyperlan wireless Ethernet link. From there, it is possible to retrieve the audio files and reprogram the acoustic sampling scheme.
The system also allows live streaming of the audio feed, thanks to custom software capable of transferring the audio input to the output of a remote Ethernet station in a lossless format (without quality loss).
The metal box containing the recording system.
