The ever-evolving role of hydrophones

What’s a hydrophone?

Hydrophones are specialised underwater microphones designed to detect, process and record sound waves in aquatic environments. Converting pressure variations into electrical signals, they are an essential tool for underwater surveillance and marine research.

What types of hydrophones are available?

There are two core categories of hydrophone: active and passive, with variations between these two categories.

Passive hydrophones monitor for soundwaves underwater such as marine mammal communication, waves or ship noise.

Active hydrophones emit sound waves, usually in the form of a sonar pulses, and then listen for the echo of the soundwaves to bounce back from objects in the water. This method helps to detect, locate and map underwater objects, and to measure the distance between two points with great precision.

What are the applications of hydrophones?

• Underwater mapping
• Submarine communication and detection
• Integration with sonar systems
• Monitoring for illegal fishing
• Offshore renewable energy planning
• Environmental monitoring
• Scientific research such as aquatic animal tracking

How to choose a hydrophone?

Before choosing a hydrophone there are several factors to be considered including:

Bandwidth: Hydrophones are available for low frequency applications such as underwater communications and geological noise monitoring e.g. sea floor and tectonic plate movement, In the higher bandwidths, hydrophones are optimised to detect the high frequency clicks and whistles of marine mammals and the sonars and echo sounders widely used by industry and recreational vessels.

Sensitivity: Noise in our oceans can range from low energy (e.g. the sounds fish make when they are feeding) to high energy (e.g. windfarm construction noise). Hydrophone sensitivity can be adjusted to better deal with low and high energy noise. For example, high sensitivity hydrophones will often be more suitable for listening to low volume noise, and vice versa.

Directionality: Hydrophones can be either omnidirectional, picking up sound from every direction, or directional, picking up sound from a fixed direction only.

Depth: Hydrophones are configured to operate at a range of depths, from shallow coastal seas to the deep ocean.

What can hydrophones be paired with?

• Autonomous underwater vehicles (AUVs)
• Uncrewed Surface Vehicles (USVs) and drones
• Survey vessels
• Buoy systems
• Vessels of opportunity

Hydrophones past and present

Hydrophones have a long history, from defence applications to the preservation of endangered species – there are plenty of uses. Here’s a brief history of where hydrophones started and where they are today.

Hydrophones: a key tool in naval defence

First deployed in 1914 to detect enemy ships and icebergs, hydrophones have played a critical role in naval defence for over 100 years.

In WW1 the navy was met with a significant challenge: the inability to detect enemy submarines, posing a huge threat to the security of the country. The solution was to detect sound underwater, from afar; this marked the beginning of underwater acoustic monitoring.

With technology progressing rapidly over the last hundred years, hydrophones remain an indispensable tool in naval defence today. Adaptability makes them crucial for maintaining security in a world of complex and evolving threats.

How are hydrophones used today?

Hydrophones are an essential tool for detecting sound underwater at great depths and distances in maritime domain awareness (MDA). For example, the monitoring of noise in the world’s oceans, seas and waterways to ensure safe and legal maritime compliance, and in the field of ocean conservation.

How hydrophones are protecting endangered species

Marine mammal monitoring is crucial for species conservation, enabled by ocean science research which often centres around underwater noise monitoring.

Hydrophones are a vital tool used to detect sound from endangered species like the North Atlantic Right Whale. Detecting low and high-frequency sounds, hydrophones are used by researchers to understand more about the behaviour of these creatures, their migration routes, feeding grounds, any potential threats to their environment.

North Atlantic Right Whales are a critically endangered species, with fewer than 350 individuals estimated to remain. Their survival is crucial to maintaining biodiversity and to preventing extinction of this important species.

Whale populations are subject to many human-related threats such as entanglement in fishing equipment, vessel collisions and climate change – all of which have contributed to altered migratory patterns, diet and breeding behaviour.

Marine mammal mitigation and renewable energy

The booming renewable energy industry has grown exponentially over the last decade. While offshore renewable energy and offshore wind is a much-needed solution to sustainable energy supply, marine mammals and their habitats are highly protected and can be impacted by offshore development.

Therefore, offshore construction and offshore development is a highly regulated and controlled industry, with environmental impact assessment and the use of underwater acoustic monitoring a key element of offshore development.

Common activity that disrupts marine mammals:

• Seismic survey
• Pile driving
• Ship noise

Hydrophone systems play a key role in monitoring for marine mammals at risk of potential harm from offshore activities and help inform developer compliance with environmental and conservation guidelines and regulations.

Conclusion

From the early days of hydrophone use to the present, hydrophones have provided valuable and important data to inform ocean science, conservation and maritime security. With technology continuing to develop at a rapid rate, there remains much potential for new acoustic technologies to provide greater insights into the sustainable use of our ocean enterprise.

To learn more about the hydrophones we offer, please view the product page.