What Are Sonar Applications?

Sonar applications are the practical uses of sound navigation and ranging technology in defense, scientific, commercial, and industrial contexts. Because acoustic waves propagate efficiently through water while electromagnetic signals do not, sonar is the dominant sensing technology in underwater environments, and its applications span a range from submarine detection and port security to seafloor mapping and fisheries management. Sonar applications draw on signal processing, oceanography, underwater acoustics, and transducer engineering, and continue to expand as autonomous underwater vehicles reduce the cost of deploying sonar systems to previously inaccessible depths and locations.

Navigation and Positioning

Sonar navigation encompasses a family of techniques used to determine position, measure water depth, and guide vessels and autonomous vehicles through underwater terrain. Echo sounders, which transmit a pulse downward and measure the two-way travel time to the seafloor, have been used since the 1920s for hydrographic surveying. Multibeam echo sounders, which fan out dozens to hundreds of beams across the seafloor simultaneously, are the standard tools for modern bathymetric mapping and have been used to chart the mid-ocean ridge system and map submarine hazards to shipping. Doppler velocity logs use the frequency shift of acoustic returns from the seafloor or water column to measure a vehicle's velocity with high accuracy. Acoustic positioning systems such as long baseline (LBL) and ultra-short baseline (USBL) allow autonomous underwater vehicles and remotely operated vehicles to determine their position relative to a network of bottom-mounted transponders, supporting precision operations in offshore energy infrastructure and search and recovery. The NOAA Ocean Exploration program describes many of these navigation and mapping techniques in the context of deep-sea survey operations.

Detection and Surveillance

Active and passive sonar systems are fundamental tools for military and security applications. Naval surface ships and submarines use hull-mounted and towed sonar arrays to detect submerged threats and to maintain awareness of the acoustic environment. Passive towed array systems operating in the low-frequency band, from tens to a few hundred hertz, exploit the machinery noise radiated by submarines to localize and track targets over ranges of tens to hundreds of kilometers. Port and harbor protection systems deploy fixed acoustic sensor networks on the seafloor to alert security personnel to unauthorized underwater vehicles or divers. Mine countermeasures sonar identifies mine-like objects on the seafloor using high-frequency active imaging systems that produce acoustic images with sufficient resolution to distinguish mine shapes from rocks and debris. The Acoustical Society of America's journal JASA publishes foundational research on detection methods and acoustic propagation models underpinning these systems.

Scientific and Commercial Uses

Outside of defense, sonar supports a broad range of scientific and commercial activities. Fisheries acoustic surveys use calibrated echo sounders operating at frequencies between 18 kHz and 200 kHz to estimate fish school biomass by measuring the acoustic backscatter from fish swim bladders, enabling stock assessments without the mortality of net sampling. Side-scan sonar produces mosaic images of the seafloor that reveal sediment type, benthic habitat, and the locations of shipwrecks, pipelines, and cables. Sub-bottom profilers penetrate the top few meters of seafloor sediment using low-frequency chirp signals to reveal stratigraphy relevant to geotechnical engineering and archaeological surveys. Marine mammal researchers use passive acoustic monitoring to track whale and dolphin populations. The NOAA-affiliated Discovery of Sound in the Sea project provides an overview of these scientific sonar applications and their interaction with the ocean acoustic environment.

Applications

Sonar technology is applied in a range of fields, including:

• Naval defense and submarine warfare
• Autonomous underwater vehicle guidance and survey
• Offshore oil and gas pipeline and infrastructure inspection
• Marine mammal monitoring and bioacoustics research
• Hydrographic charting and nautical safety
• Search and recovery operations for downed aircraft and vessels