Characterization of acoustic detection efficiency using a gliding robotic fish as a mobile receiver platform

Osama Ennasr,Christopher Holbrook,John Thon,Demetris Coleman,Xiaobo Tan,Darryl W Hondorp,Charles C Krueger,Pratap Solanki

doi:10.1186/s40317-020-00219-7

Osama Ennasr, Christopher Holbrook + Show 6 more

Open Access

https://doi.org/10.1186/s40317-020-00219-7

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Abstract

BackgroundAutonomous underwater vehicles (AUVs) and animal telemetry have become important tools for understanding the relationships between aquatic organisms and their environment, but more information is needed to guide the development and use of AUVs as effective animal tracking platforms. A forward-facing acoustic telemetry receiver (VR2Tx 69 kHz; VEMCO, Bedford, Nova Scotia) attached to a novel AUV (gliding robotic fish) was tested in a freshwater lake to (1) compare its detection efficiency (i.e., the probability of detecting an acoustic signal emitted by a tag) of acoustic tags (VEMCO model V8-4H 69 kHz) to stationary receivers and (2) determine if detection efficiency was related to distance between tag and receiver, direction of movement (toward or away from transmitter), depth, or pitch.ResultsDetection efficiency for mobile (robot-mounted) and stationary receivers were similar at ranges less than 300 m, on average across all tests, but detection efficiency for the mobile receiver decreased faster than for stationary receivers at distances greater than 300 m. Detection efficiency was higher when the robot was moving toward the transmitter than when moving away from the transmitter. Detection efficiency decreased with depth (surface to 4 m) when the robot was moving away from the transmitter, but depth had no significant effect on detection efficiency when the robot was moving toward the transmitter. Detection efficiency was higher when the robot was descending (pitched downward) than ascending (pitched upward) when moving toward the transmitter, but pitch had no significant effect when moving away from the transmitter.ConclusionResults suggested that much of the observed variation in detection efficiency is related to shielding of the acoustic signal by the robot body depending on the positions and orientation of the hydrophone relative to the transmitter. Results are expected to inform hardware, software, and operational changes to gliding robotic fish that will improve detection efficiency. Regardless, data on the size and shape of detection efficiency curves for gliding robotic fish will be useful for planning future missions and should be relevant to other AUVs for telemetry. With refinements, gliding robotic fish could be a useful platform for active tracking of acoustic tags in certain environments.

Highlights

Autonomous underwater vehicles (AUVs) and animal telemetry have become important tools for understanding the relationships between aquatic organisms and their environment, but more information is needed to guide the development and use of AUVs as effective animal tracking platforms
We describe detection efficiency of an acoustic telemetry receiver mounted on a gliding robotic fish, a novel type of underwater AUV [19,20,21], during a series of field trials in a freshwater lake conducted principally to evaluate hardware and software changes during development
Estimated detection efficiency of the robot-mounted receiver was lower than concurrently operated stationary receivers during all three runs where stationary receivers covered the full range of mobile runs (Fig. 5 a, c, d)

Summary

Introduction

Autonomous underwater vehicles (AUVs) and animal telemetry have become important tools for understanding the relationships between aquatic organisms and their environment, but more information is needed to guide the development and use of AUVs as effective animal tracking platforms. Ennasr et al Anim Biotelemetry (2020) 8:32 and their movements typically are tracked by stationary networks of hydrophones or acoustic receivers that can identify acoustic-tagged animals in their vicinity [3,4,5,6]. Acoustic telemetry enables more frequent observation (or sampling) of individuals than what can be obtained by direct observation or sampling with traditional survey methods (i.e., trawls, gill nets). Observations from such networks have already been used to improve control and assessment of invasive species, gain new insights into spawning behavior and habitat requirements of fish, and describe movements of high-valued stocks [1, 6]. Logistical and economic constraints may preclude use of stationary receiver networks to fill gaps in understanding of animal movements, especially in large systems and extreme environments

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