Passive Acoustics vs Active Sonar: Which Is Right for Your Marine Research Project?

What Is Passive Acoustic Monitoring (PAM)?

Passive acoustic monitoring (PAM) is a method of listening to underwater soundscapes without transmitting any sound into the environment. Instead, it captures naturally occurring sounds-from whale songs and dolphin clicks to ship traffic and seismic activity-using sensitive underwater microphones called hydrophones.

This non-intrusive approach is widely used in marine research, particularly when the goal is to observe without influencing the behavior of wildlife. PAM systems are often deployed on moorings, buoys, or autonomous platforms and can record continuously for weeks or even months.

Common Applications Include:

• Marine mammal detection and tracking. PAM enables researchers to identify species, study migration routes, and monitor population health by recognizing vocal patterns and call frequencies.
• Ocean noise pollution monitoring. It helps quantify the impact of human-made noise-like shipping, drilling, or construction-on sensitive marine ecosystems.
• Behavioral studies. By listening in, scientists can observe how marine animals communicate, forage, navigate, and respond to environmental changes.
• Environmental impact assessments. PAM provides baseline and ongoing acoustic data to evaluate the effects of marine development projects.
• Long-term ecological monitoring. With low power consumption and long deployment times, PAM is ideal for collecting extended datasets for climate, biodiversity, and ecosystem research.

Key Advantages

• Non-intrusive. It does not introduce any artificial sound, allowing researchers to study marine life in a natural state.
• Efficient for long-term deployments. Ideal for remote or deep-sea applications where maintenance access is limited.
• Highly effective at capturing biological and environmental sounds. From blue whale calls to shifting ice and underwater earthquakes.
• Energy efficient. Requires minimal power, making it compatible with solar or battery-based deployments.

Limitations to Consider

• No distance or location data by default. Unlike sonar, PAM cannot determine how far away a sound source is without triangulation.
• Dependent on sound-producing targets. Silent objects or species that don't vocalize may go undetected.

At Turbulent Research, our TR-PORPOISE and TR-FLOAT platforms are built to meet the highest standards of acoustic clarity and reliability. With exceptional sensitivity and ultra-low noise electronics, these systems deliver high-resolution sound data-even in noisy or challenging offshore conditions. Whether you're monitoring for regulatory compliance or leading a biodiversity study, our PAM systems offer the tools to capture sound science, literally.

What Is Active Sonar?

Active sonar is a technique that sends out sound pulses—often called “pings”—into the water and listens for the echoes that bounce back after hitting objects or surfaces. By analyzing the time delay and characteristics of these returning echoes, researchers can determine the distance, size, shape, and movement of underwater features and targets.

Unlike passive acoustic monitoring, which listens to existing sounds in the environment, active sonar creates its own acoustic signal. This makes it especially valuable in situations where the goal is to locate, map, or quantify underwater structures or objects that don’t produce sound themselves.

Common Applications Include:

• Seafloor topography mapping. Bathymetric sonar systems provide detailed images of the ocean floor, supporting everything from habitat classification to undersea cable route planning.
• Locating underwater objects. From sunken vessels to lost equipment, active sonar is crucial in search and recovery missions.
• Ice thickness and underwater structure monitoring. Used in polar and subsea engineering projects to assess environmental risks.
• Fish stock assessments. Fisheries use sonar to estimate biomass and track fish school behavior.
• AUV/ROV navigation. Autonomous and remotely operated vehicles often rely on active sonar to avoid obstacles and maintain precise positioning.

Key Advantages

• Provides real-time spatial data. Measures distance and shape of targets with high accuracy.
• Effective for non-emitting objects. Ideal for detecting silent or motionless features like rocks, pipelines, or debris.
• Versatile across depths and conditions. Can be tuned for various frequencies and ranges depending on the mission.

Limitations to Consider

• Potential to disturb marine life. Emitted pulses may interfere with or stress sensitive species, particularly marine mammals.
• Higher power consumption. Active systems typically require more energy, which can limit deployment duration or require external power sources.
• Not ideal for sensitive ecosystems. In protected or heavily regulated zones, active acoustic emissions may be restricted.

While active sonar offers a powerful way to “see” underwater, it’s essential to weigh its technical benefits against environmental considerations. At Turbulent Research, we work closely with clients to ensure that acoustic systems are tuned for both scientific precision and ecological responsibility—whether that means integrating active sonar into multi-sensor platforms or supplementing it with passive acoustic tools.

How to Choose: Passive Acoustics vs Active Sonar Questions to Ask

Here are a few key questions to help guide your decision:

• What are you trying to detect?
  → Sounds from marine mammals or ambient noise = Passive
  → Physical objects or structures = Active
• Is minimal disturbance important?
  → Use PAM in protected areas or for behavioral studies.
• Do you need real-time positioning or range data?
  → Choose active sonar if you need precise spatial data quickly.
• What’s your power budget?
  → Passive systems are more energy-efficient and better for long-term deployments.

Why Not Both?

In some projects, a hybrid approach offers the best results. For example, you might use PAM to track whale vocalizations while simultaneously using active sonar to avoid collisions or map habitat features.

At Turbulent Research, we can help design integrated systems that bring both methods together, giving you the most complete picture of what’s happening underwater.

Both passive acoustic monitoring and active sonar play vital roles in marine science and monitoring. The best choice depends on what you’re listening for, where you’re working, and how much interaction with the environment is acceptable.

Need help choosing or designing a system? Get in touch with our team, we’re always happy to help guide your next deployment.