The DARU-2515 is an autonomous data recording unit for deepwater deployments (up to 2000 m) and wide-area surveillance. The DARU-2515 is an updated and modified variant of DARU-2330. The system consists of a Digital Acoustic Surveillance Array (DASA) connected to a deployed platform containing batteries and controller electronics. The DARU is temporarily deployed to an area where it will record continuously, at scheduled intervals, or as instructed via an acoustic data link.

The acoustic array is 500 m long and contains 64 low-frequency hydrophones installed at customer-specified positions along the cable. The system also has one (1) high-frequency hydrophone with a frequency response of 100 Hz - 19 kHz when sampling at 40 kSps.

The array connects to a Data Collection Unit (DCU) and Battery Case contained in a deployment frame that is lowered to the seabed. The system will operate and record continuously for more than 8 weeks or up to six months using an intermittent recording schedule. Software in the DCU allows the operator to configure different operating states during deployment and send system status information or health queries over an acoustic modem link. The DCU Pressure Case has dedicated internal space, power connections, and a data network for a customer-installed auxiliary processing unit.

Area Surveillance and Tracking

DARU can be used for large area monitoring and target tracking by deploying two orthogonal arrays in the area of interest. Bearings from each array provide cross fixes that build target tracks for surveillance and area awareness.

Time Synchronization

The array controller synchronizes hydrophone samples across all sensors and locks timestamps the data to a disciplined chip-scale atomic clock.

Hydrophones

The LF hydrophones for the DARU are a low-noise, low power design with an acoustic bandwidth from 6 Hz to 5 kHz. The hydrophones attach to molded breakouts on the array cable and are held in place by a protective plastic shroud. The hydrophone pressure vessel is constructed from Grade 2 Titanium and is designed for long-duration, deep water deployments. The hydrophone electronics are gain matched and simultaneously sampled.

Side Channel Data

In addition to the acoustic samples, sensors within hydrophones and DCU measure and record diagnostic and auxiliary information including voltage, power usage, battery level (when applicable), hydrophone orientation, internal case temperature, pressure, and humidity.

Array Receiver

The DARU acoustic array connects to a Data Collection Unit (DCU) that manages the array power, receives sensor samples from array data buses, and computes diagnostic and health monitoring records. If enabled, the ARC will also run data processing algorithms, and record data to solid-state storage.

Additional Sensors

The DARU sensor bus format supports many different sensor types that can be included with the acoustic array. The system can add one or more high-frequency hydrophones (up to 192 kSps). Three-axis magnetometers can be installed in place of acoustic array channels. The acoustic channels can be configured over one or more arrays in any geometry. Systems have been configured with horizontal, vertical, circular, and orthogonal 3-axis arrays.

Data Processing

The DARU Data Collection Unit (DCU) runs a custom Linux operating system on a dual-core ARM Cortex-A9 processor with an FPGA coprocessor. The DCU software includes functions for array operation, logging, scheduling, health monitoring, and energy/event detectors. Omnitech Electronics provides user support and comprehensive interface definitions and data API’s that users can use to integrate additional functionality and data processing. Users can use spare processing on the DCU or add a separate coprocessor.