What is the Difference Between Active and Passive Acoustic?

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difference between active and passive acoustic

In the ocean’s vast expanse, acoustics emerge as a central element shaping humanity’s interactions with marine life and the underwater environment. Ocean acoustics is the study of sound and its behavior which is characterized by two operational modes: active (sound emission), and passive (sound reception and interpretation). Integrating both active and passive acoustic technologies within a versatile network can unlock discoveries and deepen understanding of sea habitats’ health, biodiversity, climate changes, marine hazards, and maritime safety. What’s the difference between active and passive acoustic methods, and how can they be used to understand more about underwater science and protect ecosystems?

Active Acoustic Techniques

Although humans have been aware of sound and its properties since ancient times, the scientific study of sound, known as acoustics, began to emerge as a discipline in the 17th century. Pioneers like Robert Boyle and Ernst Chladni conducted experiments on sound propagation and resonance, laying the groundwork for future research.


In aquatic environments, active acoustic systems typically use specialized devices called transducers to generate and project sonar waves, which then bounce off objects or sea organisms, allowing for the measurement of distances, depths, or the detection of targets. The technology finds applications in various fields, including navigation, fishery science, mapping, and submarine detection.

Power Requirement

This structure demands higher power levels as they involve transmitting intense signals into the environment and processing the returning echoes. These mechanisms require robust energy sources to generate and sustain sound waves, making them suitable for immediate surveillance and precise measurements in various applications.


The techniques find wide application in tasks such as navigation, depth sounding, and fish detection. They excel in real-time tracking, providing immediate feedback on underwater conditions. Active systems are commonly used in fisheries management, oceanographic research, and resource exploration due to their ability to probe the environment.


This involves emitting sound pulses and analyzing the returning echoes in real-time. As it provides immediate feedback on conditions, the approach is suitable for tasks like fish tracking, habitat mapping, and navigation.


Using sonar technology to detect their presence, assess abundance, and monitor behavior, the techniques are employed for studying various oceanic fauna, including fish, Krill, Zooplankton, and Benthic Organisms. This method allows for targeted surveys and efficient collection, contributing to fisheries management and ecological research in ecosystems worldwide.

Marine Mammals

Active acoustic techniques are used to study marine mammals by emitting sound pulses and analyzing the returning echoes. This allows for the detection, tracking, and behavioral analysis of mammals such as whales, dolphins, and seals, aiding in conservation efforts and understanding their ecological roles.

Passive Acoustic Techniques


Passive acoustic techniques typically use hydrophones or other sensitive sensors to capture and record sounds generated by sea organisms, geological processes, or human activities. These practices do not emit any signals themselves but instead rely on listening to the environment to gather information. Passive technology finds applications in various fields, including mammal surveillance, oceanography, underwater surveillance, and communication.

Power Requirement

In contrast, a passive system operates with significantly lower power requirements. They don’t project signals but rely on sensitive sensors to capture and analyze ambient noise. This low-energy operation enables extended deployment durations, making passive ideal for long-term surveillance of ecosystems without causing disturbance to marine life.


The methods are used for long-term tracking of environments, including studying marine mammal behavior, tracking animal migrations, and monitoring oceanographic phenomena like aquatic earthquakes or whale vocalizations.


The surveillance relies on the continuous detection and analysis of naturally occurring sounds without actively emitting any signals. It is used for long-term surveillance of marine environments, including studying mammal behavior, detecting sea creatures, and monitoring underwater noise pollution.


The approaches are valuable for studying a wide range of oceanic species, particularly mammals, by capturing their vocalizations and behaviors without direct interaction. This non-invasive method enables long-term surveillance of species presence, distribution, and communication patterns.

Marine Mammals

Passive acoustic methods capture the vocalizations and behaviors of marine mammals without disturbing them. This non-invasive approach enables prolonged observation of aquatic organisms, distribution, and communication patterns, contributing to conservation efforts and understanding the ecological dynamics of mammal populations.

acoustic monitoring at sea

Future Directions in Marine Acoustic Technologies

The use of sound for underwater communication and navigation traces back to the early 20th century. During World War I, hydrophone devices capable of detecting sound waves were developed for military purposes, primarily for detecting submarines.

Advancements in Active Acoustic Techniques

Innovations have played a pivotal role in expanding our understanding and exploration of the underwater realm. These advancements have revolutionized observations and interactions with the marine environment, offering new insights into its complexities and dynamics. Some key advancements include:

Higher Frequency Systems: Technological improvements have allowed for the development of active systems operating at higher frequencies. These approaches provide finer-resolution imaging, making them invaluable for detailed seafloor mapping, habitat characterization, and detection of small objects.

Multibeam Sonar: The technology has evolved to provide high-resolution, three-dimensional imaging of the seafloor and water column. These methods use multiple beams to simultaneously survey a wide swath of the ocean floor, increasing efficiency and accuracy in mapping features such as canyons, ridges, and seamounts.

3D Visualization: Advancements in data processing and visualization techniques enable the creation of three-dimensional representations of underwater environments using active figures. These 3D models offer researchers and oceanographers a more intuitive and immersive way to explore and analyze topography and habitat structures.

Real-time Data Processing: The practices now feature advanced real-time data processing capabilities, allowing for immediate analysis and interpretation of signals. This enables rapid decision-making in applications such as navigation, exploration, and search and rescue operations.

Autonomous Platforms: Active systems are now being deployed on autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs), enabling autonomous collection in remote or hazardous environments. These platforms enhance survey efficiency and accessibility while reducing the need for human intervention.

Innovations in Passive Acoustic Technologies

These innovations have expanded the capabilities and applications of underwater monitoring. Some notable innovations include:

Miniaturization of Hydrophones: Advances in materials science and engineering have led to the development of smaller and more sensitive hydrophones. Miniaturized hydrophones are easier to deploy and can be integrated into compact platforms, such as buoys, gliders, and AUVs.

Wideband and Directional Hydrophones: Innovations in hydrophone design have resulted in wideband and directional hydrophones that can capture a broader range of frequencies and isolate sound sources from specific directions. These hydrophones enhance the ability to detect and localize sounds, facilitating applications such as marine mammal monitoring, seismic detection, and communication.

Acoustic Telemetry Systems: Also called Ultrasonic Telemetry techniques, they have been developed to track the movements and behavior of oceanic animals using passive signals.

Sinay's Role in Advancing Active and Passive Acoustic Technologies

Sinay’s state-of-the-art sonar systems are globally recognized for their accuracy and dependability in underwater surveillance. These innovative techniques utilize leading-edge technology to detect submerged objects, navigate intricate marine landscapes, and identify potential risks.

Advancing Connectivity Infrastructure: Sinay has been instrumental in advancing connectivity infrastructure, exemplified by groundbreaking initiatives like the PAM buoys. These interconnected networks facilitate seamless communication among maritime vessels, sensors, and coastal facilities, fostering real-time cooperation and informed decision-making.

Harnessing Analytical Capabilities: Sinay harnesses advanced analytical capabilities driven by artificial intelligence and machine learning to dissect extensive maritime data sets. These cutting-edge platforms convert raw information into actionable intelligence, empowering organizations to streamline operations, minimize environmental impact, and safeguard marine biodiversity.

Championing Environmental Responsibility: Sinay remains steadfast in its commitment to promoting environmental stewardship across maritime activities. Through the provision of advanced technologies and solutions, Sinay assists enterprises in reducing their environmental footprint, preserving marine ecosystems, and meeting regulatory standards.

Driving Innovation and Research: Sinay dedicates significant resources to ongoing research and development efforts aimed at enhancing monitoring technologies and tackling emerging challenges in oceanic oversight. By remaining at the forefront of innovation, Sinay ensures that its solutions continue to deliver effectiveness, reliability, and adaptability to evolving maritime demands.



Acoustic sciences are integral to comprehending the ocean’s depths, informing interactions with marine organisms and the underwater landscape. Central to this is the distinction between active and passive techniques, each offering unique insights into the mysteries of the deep. Integrating these methods can lead to discoveries and help advance efforts to preserve ecosystems.

Frequently Asked Questions About Passive and Active Acoustic

Active acoustic refers to a method of underwater sensing or navigation that involves emitting sound pulses and analyzing the returning echoes to gather information about the surrounding environment, such as water depth, bottom composition, and the presence of objects or marine life.

Passive acoustic refers to a method of underwater sensing or monitoring that relies on listening to sounds generated naturally in the environment, such as marine mammal calls, fish vocalizations, or vessel noise, without actively emitting any sound signals.

Active acoustic offers the advantage of controlled signal transmission, allowing for precise measurements and the ability to gather specific information about the underwater environment. It is particularly useful for tasks such as depth sounding, fish stock assessment, and underwater mapping.

Passive acoustic monitoring is often used for long-term environmental monitoring, marine mammal studies, and detecting natural or anthropogenic sounds in the ocean, while active acoustic is more commonly employed for real-time navigation, fisheries research, and underwater surveillance requiring immediate data feedback.

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