CASCADE Aerial robotics for acoustic sensing in complex environments

Freshwater ecosystems provide essential ecosystem services including food and clean water and despite covering just 1% of the earth surface, support over 10% of all species on earth. These ecosystems are in crisis, with an average 84% decline in freshwater population abundance and 1 in 3 species at risk of extinction. Monitoring and evaluating the response of ecosystems to anthropogenic change is essential for effective management and improved decision making. The emerging field of passive acoustic monitoring (PAM) is helping biologists to collect data on vocal species at greater spatial and temporal extents, whilst reducing the required person-power and invasiveness of studies. However in fresh water ecosystems the installation of recording devices is limited to the banks of ponds, lakes or rivers, or for larger areas, on floating devices in open water. Access to the bankside of freshwater ecosystems can be restricted or can cause environmental damage and installing sensors on buoys in open water are limited to locations where the buoys are present or can be installed and can disturb the environment through their installation.

Fig.1 Sail-Flight cycle. The robot lands on water where it transitions to sailing and i accomplishes the sailing mission. Take off and flight are then achieved via propeller acceleration.

Recently a team of researchers from Aerial robotics lab, Imperial conducted a research study at nature park Vransko jezero in Croatia and spent over eight days collecting data on lake Vrana, the largest freshwater ecosystem in Croatia and did passive acoustic monitoring using aerial aquatic robotic system SailMAV.

SailMAV is an aerial-aquatic robot that can sail and fly autonomously (Fig. 1). It’s been developed with an adaptive morphology, which allows it switch between two configurations: one used for flight, and one used for sailing. It is composed of two hulls connected by a central wing in a catamaran configuration, one is used for flight/sailing control and navigation, while the other encloses sensors used to sensing the local wind and other environmental variables such as water temperature, air temperature, humidity, atmospheric pressure. SailMAV sails in a fully autonomous mode which is based on pre-programmed missions of GPS coordinate waypoints. SailMAV was fitted with both underwater and surface acoustic recorders to record both underwater and above water biodiversity in freshwater ecosystems (Fig.2).

Fig. 2 SailMAV in sailing mode (left) and take off mode (right)

During 12 successful missions across eight days SailMAV travelled 32.2 km and collected 2263 minutes of acoustic recordings, 929 of underwater recordings and 1334 of surface bird recordings. Of these, 956 minutes were collected in disturbed sites and 1307 minutes in the protected ornithological area. Soundscape and species-based analysis were able to provide important insights on aquatic biodiversity, showing higher bird diversity and increased underwater biotic acoustic activity in the protected ornithological reserve, highlighting the importance of this protected area and providing a baseline for future studies.

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