Abstract
The collective understanding of the environmental implications for large-scale deployment of marine renewable energy technologies remains incomplete [1]. Filling these gaps requires instrumentation able to detect events that occur rarely, but with high consequence (e.g. collision between a marine mammal and a turbine), as well as events that occur frequently, but may only be biologically significant when considering cumulative exposure (e.g. a marine mammal within an area of elevated noise) [2].
The intelligent Adaptable Monitoring Package (iAMP) is an integrated instrumentation package that combines a suite of instruments for advanced environmental monitoring capabilities [3,4]. The iAMP (shown in Figure 1a) integrates data streams from optical cameras, multibeam sonars, an array of hydrophones, a fish tag detector, and an acoustic Doppler current profiler (ADCP) into a uniform software interface.
The iAMP instruments are selected to provide comprehensive data about the environment around a marine energy device. The hydrophone array is capable of detecting marine mammal vocalizations to a range of several hundred meters (site and animal dependent). There are two multibeam sonar devices: a Kongsberg M3 (500 kHz) and a BlueView M-series (dual frequency, 900 or 2250 kHz). The M3 can operate at up to 150 m range, and the Blueview 2250 kHz head provides higher resolution imaging within a 10 m range. Optical cameras allow for species classification to a range of up to 8 m (site dependent). The ADCP, a Nortek Signature (500 kHz), provides additional environmental context by monitoring the currents and waves at a site.
Drivers for all iAMP instruments are implemented in National Instruments LabView to centrally control instruments and data acquisition. Data from each instrument is stored in a ring buffer (up to 60 seconds of storage). When a target (e.g. fish or marine mammal) is detected or a save event is generated by a duty cycle timer, all ring buffers are written to disk after a fixed time has elapsed. Use of ring buffers, as opposed to beginning recording when a target is detected, ensures that the entire event is captured (e.g., a 60-s buffer might include 10 s of data prior to event detection and 50 s of data following). This also allows time for target detection algorithms to run without generating a backlog of data.
Continuous data acquisition from all iAMP instruments would produce over 250 GB of data per hour, presenting challenges for both data storage and post-processing. It is preferable for automatic target detection and classification algorithms to limit data acquisition to periods of interest. Detection and tracking of fish and marine mammals on the two multibeam sonar heads (BlueView M900-2250 and Kongsberg M3) will be handled by the Nekton Interaction Monitoring System (NIMS), software developed in collaboration between the Pacific Northwest National Laboratory (PNNL) and the University of Washington. Marine mammal vocalizations are detected by the hydrophone array, and will be classified in PAMGuard (http://www.pamguard.org), an open source software package for passive acoustic monitoring of cetaceans. Development and application of triggering algorithms requires training data to allow the selection of thresholds that limits the number of false positives while still capturing most actual events.