Working with Canadian industry, Ocean Networks Canada Innovation Centre helps new technologies adapt for use on observatory platforms, by providing expertise to demonstrate and highlight new instruments for the global market. As a vital component of a world-class ONC ocean observing system, DIGITAL HYDROPHONES were identified as a high priority technology by the ONC science and engineering teams, and represent a significant global growth market.

Instrument Concepts based near Truro, Nova Scotia, has developed new state-of-the-art, fully integrated digital “smart” hydrophones with GeoSpectrum Technologies' transducers—making them ideal candidates for Innovation Centre technology demonstrations. A smart hydrophone is a highly sophisticated underwater microphone capable of digitizing sound, calculating the energy at each frequency, sending data out via the Internet, and even creating alerts for specific events, such as whale calls.

Following lengthy evaluation and calibration, the Sensor and Instrument team at Ocean Networks Canada Innovation Centre’s technology demonstration facility is today reporting impressive results from calibration tests with the company’s icListen LF hydrophone. “We ran this hydrophone through an extensive battery of laboratory and field tests. Given the impressive specifications in the manufacturer’s brochure, we were very pleased to find that the manufacturer’s impressive performance claims were exactly on the mark.” says Tom Dakin, the Innovation Centre’s Sensor and Technology Business Development Officer and resident ocean acoustician. “I have to tip my hat to the Instrument Concepts engineers.”

For many years, acoustical oceanographer Dr. Ross Chapman has been interested in making measurements of low frequency ambient noise in the ocean. According to Chapman, Professor Emeritus at the University of Victoria, it is difficult to design a measurement system that can provide quality data. "The system needs a huge dynamic range to cover the complete picture in the soundscape," he says, "from the deafening throbs of close-by passing ships to the ultra-quiet distant background."

"I've used many different phones on different systems, but these icListen hydrophones are the best I've seen in many years," adds Dr. Chapman. "They're calibrated to very low frequencies where I've never been able to get reliable data."

New calibration system is unique in the world

The Ocean Networks Canada Innovation Centre began designing a test plan in May 2011 to independently verify the manufacturer’s specifications and explore this instrument’s capabilities. However, there were no existing facilities capable of performing tests for the unique capabilities of the icListen LF. So the Innovation Centre's S&T team developed the world’s first low frequency, digital hydrophone calibration facility. “Calibration at low frequencies is not an easy task,” says Dr. Chapman. “The Innovation Centre's calibration facility confirms my impression of the iclisten instrument.”

This automated calibration system can very accurately assess the hydrophone’s performance from 0.02 Hz up to 100 Hz. Testing from 100 to 1600 Hz was accomplished via a traditional open water reference calibration system in the acoustically quiet Saanich Inlet. Self-noise, dynamic range, linearity and field tests were also performed with excellent results.

Progressing to the sea floor

Following its initial test phase, the icListen LF was deployed to the seafloor of the Georgia Strait in December 2011, and is currently undergoing an eight-month working test phase as part of an ocean observatory. It is located on the East Node of the VENUS network in an array at a depth of 170 metres. Live audio signals from the LF model are available for viewing on the VENUS observatory network website.

The high performance and fully integrated nature of this compact hydrophone offer an attractive technology for ocean observatories and major international initiatives such as the proposed International Quiet Ocean Experiment. Key benefits include:

• The compact non-corroding pressure case
• 24 bit resolution (120dB of dynamic range)
• Low noise
• Low frequency optimization (ideally suited to measure shipping noise, earthquakes, tsunamis and large baleen whales that communicate in low frequencies over hundreds of kilometres)
• Deploys down to 3500 metres

Looking to future tests with higher frequencies

Instrument Concepts has announced a new affiliate company, Ocean Sonics, which will focus on manufacturing the icListen High Frequency Smart Hydrophone and related products. This HF model is designed for sub-sea applications such as environmental monitoring, cetacean tracking and offshore energy operations. In spring 2012, the Innovation Centre plans to begin testing the icListen HF and is developing a new 100 Hz to 100 kHz digital hydrophone calibration system to accommodate this instrument.