Sound Velocity Profilers

Within oceanography, a sound velocity profiler (SVP) is designed to measure the speed of sound in seawater. The measured sound velocity is directly influenced by factors such as the temperature, salinity and pressure, and by measuring the velocity profile throughout the water column, a sound velocity profiler is able to provide essential information about oceanographic processes such as ocean circulation and stratification.
Overview Sound Velocity Profilers
By Staff Writer Last updated: June 26th, 2024

A sound velocity profiler, often referred to as an SVP, is a type of oceanographic profiler that deploys a sound velocity sensor to capture the speed of sound in the water column. The instrument typically consists of a probe that can be lowered from a vessel or platform into the water to record sound velocity at different depths.

The SWiFT SVPplus Chlorophyll a by Valeport, a sound velocity profiler designed for coastal, harbour and inland hydrographic survey

SWiFT SVPplus Chlorophyll a by Valeport

As the probe descends, it continuously records data at various depths, providing a profile of sound velocity versus depth. This data is then used to correct and interpret acoustic signals more accurately.

By providing precise measurements of the speed of sound through seawater, SVP sensors enhance the accuracy of sonar readings, improve underwater navigation, and support a multitude of marine applications from hydrographic surveying to environmental monitoring.

Sound Velocity Profiler Components

  • Sound Velocity Sensor: This is the core component that directly measures the speed of sound. It operates based on principles such as time-of-flight or phase shift, where the time taken for a sound pulse to travel a known distance or the change in phase of a sound wave is used to calculate sound velocity.
  • Pressure Sensor: To determine the depth at which measurements are taken, the SVP includes a pressure sensor.
  • Temperature Sensor: Since sound velocity in seawater is affected by temperature, this sensor helps compensate for temperature variations.
  • Salinity Sensor: Sometimes, an additional salinity sensor is included, as salinity also impacts sound speed.

SVP Survey Applications

OEM Sound Velocity Sensor by Valeport

OEM Sound Velocity Sensor by Valeport

SVP surveys, using a sound velocity sensor on an oceanographic profiler are pivotal in advancing marine research.

Hydrographic Surveys: During an SVP survey, the profiler is deployed to obtain a detailed sound velocity profile of the survey area. This data is crucial for correcting sonar readings and improving the accuracy of seabed mapping.

Underwater Navigation: Accurate sound velocity profiles are vital for the calibration of sonar systems used in navigation, ensuring that distance measurements are precise.

Submarine Operations: Submarines rely on sound velocity data for navigation and communication. SVP marine data helps in planning routes and maintaining stealth.

Marine Construction: For underwater construction projects, understanding the sound velocity profile aids in the precise placement of structures and the accurate interpretation of acoustic signals.

Sonar Calibration: Sonar systems, whether used for fish finding, seabed mapping, or military purposes, depend on accurate sound speed data to interpret echoes correctly. Variations in sound speed due to temperature, pressure, and salinity can lead to significant errors if not accounted for.

Seismic Surveys: In oil and gas exploration, sound velocity data from SVP sensors helps in the interpretation of seismic surveys by providing context about the water column through which seismic waves travel.

Environmental Monitoring: SVPs assist in studying oceanographic phenomena like thermoclines, where sharp changes in temperature can affect marine life and sound propagation.

SVP Sensors Vs CTD

Unlike a CTD (conductivity, temperature, and depth) profiler, which measures the physical properties of seawater for oceanographic research, an SVP measures the speed of sound in water for acoustic applications.

A CTD directly measures its parameters, from which salinity and density can be derived, whereas an SVP often uses measurements of temperature, salinity, and pressure (possibly from a CTD) to calculate sound velocity.

CTDs are primarily used for climate research, biological studies, and understanding water mass distribution. They differ from SVPs, which are primarily used in acoustic systems, such as sonar and underwater communication.