Reducing the cost of fishery surveys
Scientists can investigate ocean life using many different methods. Sonar, trawls, CTD sensors, and video cameras are just a few options, along with time spent on ships or planes. These methods provide valuable information, but can be cost prohibitive. Scientists at the Northwest Fisheries Science Center are developing a new, low-cost method of researching marine life: the integrated Wave Glider-echosounder.
NWFSC's Larry Hufnagle and Dezhang Chu, in collaboration with Charles Greene from Cornell University, Liquid Robotics, Inc., and BioSonics, Inc., have integrated a Wave Glider (an unmanned marine robot) with acoustic technology to develop a new way to survey fish populations.
How does a Wave Glider Work?
A Wave Glider is an unmanned submersible propelled by waves and powered by solar panels. The Wave Glider is designed to glide through the ocean by itself for an extended period of time. Wave Gliders are controlled remotely using a computer, or even a smart phone.
Created by Liquid Robotics, the Wave Glider consists of three parts: a float, an umbilical, and a sub. The float, like its name suggests, is the part of the Wave Glider that floats on the surface of the ocean. It contains the communication devices, central computer control, and solar panels.
The umbilical connects the float to the sub, and houses a communications cable. This allows for the communication of instructions and data between the sub, instrument package, and the surface computer. The sub is completely underwater, and is made up of a body, wings that harness the wave energy to move the vehicle, and a rudder for navigation.
The movement of the float on the waves causes the wings on the sub to engage and release, which propels the vehicle. The solar panels attached to the float power the communication and navigation devices and scientific instrument packages. Data about navigation and power status are sent to land periodically via satellite.
Integrating an Echosounder with the Wave Glider
As part of the NWFSC's Acoustics Team, Hufnagle and Chu develop and use acoustic technology to research marine life. They took an acoustic tool used in fishery surveys -- an echosounder -- and added it to the Wave Glider.
The echosounder, developed by BioSonics, is attached to the sub with another umbilical and towed by the Wave Glider. The echosounder sends sound waves down into the ocean. When the sound hits an object that has different acoustic properties than seawater, such as a school of fish, it bounces back. The sound signals received by the echosounder are called backscattered acoustic data. These data are collected and stored on the echosounder for further analysis when the vehicle is recovered, and are used to assess population levels of fish species. A portion of the collected acoustic data is sent to land-based stations in almost real time via satellite. Scientists and engineers on land use this data to monitor the performance of the echosounder.
Initial tests are Successful
Hufnagle and Chu traveled to the Liquid Robotics test center in Kona, Hawaii in September 2012 to test the integrated Wave Glider-echosounder. They deployed the integrated unit off of Kona several times. Analysis of the navigational data found that the Wave Glider and echosounder functioned satisfactorily. Most importantly, they were able to identify different aggregations (groups) of fish, showing that this technology could be successfully incorporated into larger fishery surveys.
Because the Wave Glider can be deployed for long durations and operated from shore, it offers a more economical approach to supplement fisheries survey data, while using the same acoustic technology deployed from manned vessels.
Surveying Pacific Hake
Pending continued funding, the integrated Wave Glider-echosounder will be incorporated into the NWFSC's 2013 U.S.-- Canada integrated acoustic and trawl survey of Pacific hake. The Wave Glider will be deployed from the NOAA Ship Bell M. Shimada off Newport, Oregon, with a 30-45 day deployment planned to collect data on aggregations of hake, an economically important species found off the west coast of North America.