Oceanography

ADCP (Acoustic Doppler Current Profiler)

Principle

An ADCP measures the currents velocity and direction on a vertical profile.

Principle:

  • Ultrasonic signal transmission of fixed frequency along several beams.
  • Signal partly reflected by the impurities in the water column.
  • Frequency of received echo shifted by Doppler effect.
  • This shift allows to compute the speed and direction of particles and therefore speed and direction of the currents.
  • This processing occurs simultaneously at several water column levels and allows to record a current profile.

Some ADCP types allow, by precise analyze of orbital eddies generated by waves movements, to determine amplitudes period and direction of waves and swell.

Implementation and data processing

The ADCP can be installed on the seabed or close to the surface on a buoy or on a boat-hull, looking downwards.

Data can be recorded in situ in the memory of the equipment or transmitted on line to shore trough an acoustic and/or wireless modem.

Application

Real Time Utilization:

  • Aid to marine navigation and vessel berthing and mooring.
  • Sea conditions monitoring for worksite supervision, water sports, health and security of persons and goods.
  • Aid to oceano-meteorological forecast.

Offline Utilization:

  • Metocean data base design
  • Structures Dimensioning
  • Climatic Models


Exemple of ADCP utilisation

Context

A measurements campaign of water turbidity and ocean current’s speed shall be performed as part a programme for port improvement relating to dredging operations.

Book of specifications

Requested measures:

  • Ocean current speed and direction over water column.
  • Turbidity over water column.

Conditions:

  • Real time.
  • Equipment bed in on sea bottom.
  • Vandalism prevention.

Technical solution

An (Acoustic Doppler Current Profiler) is mounted on a frame bed in the sea bottom. It will measure the current profiles and includes a pressure sensor.

Turbidity sensors are mounted along a mooring line at 2m distances each other. These sensors are installed between 5m depth and 17m depth

Electrical power for both measurements is provided using a cable permitting the data transmission too. These cables are connected to an electrical cabinet on shore. The cabinet communicates to the control room using radio transmission.


Equipment overview.

Result

Measured data:

  • Currents speed and direction every 50cm.
  • Water column over the sensor.
  • Turbidity for 7 depths.

For data safety the raw data are stored into the electronic cabinet.

The monitoring can be easily performed on a single display, the software permits to archive and to visualize the measures.

Options:

  • Others sensors can be added in the same location as the turbidity sensors (conductivity, pressure depth, oxygen or temperature).
  • Up to 20 sensors can be installed on the line.
  • Directional waves measurements module can be proposed with the ADCP sensor.