Acoustic Doppler Current Profiler
Encyclopedia
An Acoustic Doppler Current Profiler (ADCP or ADP) is a sonar
that attempts to produce a record of water current velocities
for a range of depths. They are made of ceramic materials, and contain transducers, an amplifier, a receiver, a mixer, an oscillator, a clock, a temperature sensor, a compass, a pitch and roll sensor, and computer components to save the information collected. ADCPs can be configured in many ways: side-listening, into river
s and canal
s for long term continuous discharge measurements, downward-listening and mounted on boats for instantaneous surveys in the ocean
or rivers, and mounted on mooring
s, or the seabed
for long term current & wave studies. They can stay underwater for years at a time, and have a battery back for an energy source. The sonar is used for oceanography
, estuary
, river and stream
flow measurement, and weather forecasting
.
s, (or other piezo
materials) for transducers, which work in water similar to directional loudspeaker
s in air. These transducers are aimed such that the sound pulse travels through the water in different, but known directions. As the sound energy leaves and arrives at the transducer face it is shifted in frequency, known as the Doppler effect
, by the relative velocity of the water. As that sound energy is returned (echo) by scatterers in the water the sound may also be shifted in frequency if there is relative velocity of water to scatterer. Trigonometry
, averaging and some critical assumptions are used to calculate the velocity of the group of echoing scatters in a volume of water. By repetitive sampling of the return echo, and by "gating" the return data in time, the ADCP can produce a "profile" of water currents over a range of depths. Phased array
techniques are also used to aim the sound (acoustic
) energy, allowing for economical production of smaller ADCPs to accommodate a range of frequencies from 38 kHz to several megahertz.
In addition to the transducers, an ADCP typically has an electronic amplifier
, receiver
, mixer
, oscillator, accurate clock, temperature sensor, compass
, pitch and roll sensor, analog-to-digital converters, memory, digital signal processor
and instruction set. The analog-to-digital converters (ADCs) and digital signal processor (DSP) are used to sample the returning signal, determine the Doppler shift, and sample the compass and other sensors in order to calculate range and a velocity vector relative to a known orientation.
ADCPs can be self-contained and operate from batteries for many years under the sea or remotely in a river or stream. Some time later they are retrieved and the historical current data is transferred from the ADCP memory to a computer and displayed using a variety of graphical and text-based software to observe the water current profiles. Or ADCPs can be connected to RS232, RS422, RS485, SDI-12
, USB, Ethernet
, Fiber, Modbus
(SCADA) connections to provide real time, "live", monitoring of their output.
, estuary
, river and stream
flow measurement, even in weather forecasting
. ADCPs are used in diverse ways, from locating underwater "tornadoes" that might damage deep water oil drilling activity, to measuring water flow through sewer
pipes, or hanging up side down under an iceberg
and measuring the flow of freshwater
melting off the iceberg. Some harbor managers now use ADCPs to help them take advantage of tides and currents and optimize the flow of shipping in a busy port.
An ADCP can also be an acoustic Doppler Velocity Log (DVL) if it is programmed with the correct signal processing logic. The DVL bounces sound off the bottom (or a reference layer of water) and can determine the velocity vector of a subsea vehicle (or surface vessel) moving across the sea floor. This information can be combined with a starting fix
, compass heading, and acceleration sensors (typically by use of a Kalman Filter
) to calculate the position of the vehicle. DVLs are used to help navigate surface vessels, submarine
s, autonomous underwater vehicle
s, and ROV
s for precise positioning in an environment where GPS, and other navigational aids, don't work.
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
that attempts to produce a record of water current velocities
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
for a range of depths. They are made of ceramic materials, and contain transducers, an amplifier, a receiver, a mixer, an oscillator, a clock, a temperature sensor, a compass, a pitch and roll sensor, and computer components to save the information collected. ADCPs can be configured in many ways: side-listening, into river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
s and canal
Canal
Canals are man-made channels for water. There are two types of canal:#Waterways: navigable transportation canals used for carrying ships and boats shipping goods and conveying people, further subdivided into two kinds:...
s for long term continuous discharge measurements, downward-listening and mounted on boats for instantaneous surveys in the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
or rivers, and mounted on mooring
Mooring
Mooring may refer to:* Mooring , any device used to hold secure an object by means of cables, anchors, or lines* Mooring mast, a structure designed to hold airships and blimps securely in the open when they are not in flight....
s, or the seabed
Seabed
The seabed is the bottom of the ocean.- Ocean structure :Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources...
for long term current & wave studies. They can stay underwater for years at a time, and have a battery back for an energy source. The sonar is used for oceanography
Oceanography
Oceanography , also called oceanology or marine science, is the branch of Earth science that studies the ocean...
, estuary
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
, river and stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
flow measurement, and weather forecasting
Weather forecasting
Weather forecasting is the application of science and technology to predict the state of the atmosphere for a given location. Human beings have attempted to predict the weather informally for millennia, and formally since the nineteenth century...
.
Components
Depending on the field application, an ADCP may use one or more ceramicCeramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
s, (or other piezo
Piezo
"Piezo", derived from the Greek piezein, which means to squeeze or press, is a prefix used in:* Piezoelectricity* Piezoresistive effect* Piezometer* Piezo ignition* Piezoelectric sensor* Piezoelectric loudspeakers* Piezo Audio Amplifier...
materials) for transducers, which work in water similar to directional loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s in air. These transducers are aimed such that the sound pulse travels through the water in different, but known directions. As the sound energy leaves and arrives at the transducer face it is shifted in frequency, known as the Doppler effect
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
, by the relative velocity of the water. As that sound energy is returned (echo) by scatterers in the water the sound may also be shifted in frequency if there is relative velocity of water to scatterer. Trigonometry
Trigonometry
Trigonometry is a branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides. Trigonometry defines the trigonometric functions, which describe those relationships and have applicability to cyclical phenomena, such as waves...
, averaging and some critical assumptions are used to calculate the velocity of the group of echoing scatters in a volume of water. By repetitive sampling of the return echo, and by "gating" the return data in time, the ADCP can produce a "profile" of water currents over a range of depths. Phased array
Phased array
In wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
techniques are also used to aim the sound (acoustic
Acoustics
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...
) energy, allowing for economical production of smaller ADCPs to accommodate a range of frequencies from 38 kHz to several megahertz.
In addition to the transducers, an ADCP typically has an electronic amplifier
Electronic amplifier
An electronic amplifier is a device for increasing the power of a signal.It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude...
, receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
, mixer
Electronic mixer
An electronic mixer is a device that combines two or more electrical or electronic signals into one or two composite output signals. There are two basic circuits that both use the term mixer, but they are very different types of circuits: additive mixers and multiplying mixers...
, oscillator, accurate clock, temperature sensor, compass
Compass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...
, pitch and roll sensor, analog-to-digital converters, memory, digital signal processor
Digital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...
and instruction set. The analog-to-digital converters (ADCs) and digital signal processor (DSP) are used to sample the returning signal, determine the Doppler shift, and sample the compass and other sensors in order to calculate range and a velocity vector relative to a known orientation.
Performance
There are a number of factors that affect accuracy, resolution and profile range. Most notable are: absorption, spreading, speed of sound in water, bandwidth of the sound energy, signal strength of the transmitted pulse and echo, size of transducer, beam width (sic) of the energy pulse travelling through the water, frequency, and a host of limitations associated with the signal processing techniques and hardware, including clock/oscillator accuracy.ADCPs can be self-contained and operate from batteries for many years under the sea or remotely in a river or stream. Some time later they are retrieved and the historical current data is transferred from the ADCP memory to a computer and displayed using a variety of graphical and text-based software to observe the water current profiles. Or ADCPs can be connected to RS232, RS422, RS485, SDI-12
SDI-12
SDI-12 is the acronym for "Serial Data Interface at 1200 Baud". SDI-12 is an asynchronous, ASCII, serial communications protocol that was developed for intelligent sensory instruments that typically monitor environmental data...
, USB, Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
, Fiber, Modbus
Modbus
Modbus is a serial communications protocol published by Modicon in 1979 for use with its programmable logic controllers . Simple and robust, it has since become one of the de facto standard communications protocols in the industry, and it is now amongst the most commonly available means of...
(SCADA) connections to provide real time, "live", monitoring of their output.
Uses
The ADCP, commercially available for about 25 years, is currently used for oceanographyOceanography
Oceanography , also called oceanology or marine science, is the branch of Earth science that studies the ocean...
, estuary
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
, river and stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
flow measurement, even in weather forecasting
Weather forecasting
Weather forecasting is the application of science and technology to predict the state of the atmosphere for a given location. Human beings have attempted to predict the weather informally for millennia, and formally since the nineteenth century...
. ADCPs are used in diverse ways, from locating underwater "tornadoes" that might damage deep water oil drilling activity, to measuring water flow through sewer
Sewer
Sewer may refer to:* Part of sewerage, the infrastructure that conveys sewage*Effluent sewer, a collection system that transports only the liquid portion of wastewater through small-diameter pipes laid at contour...
pipes, or hanging up side down under an iceberg
Iceberg
An iceberg is a large piece of ice from freshwater that has broken off from a snow-formed glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice...
and measuring the flow of freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
melting off the iceberg. Some harbor managers now use ADCPs to help them take advantage of tides and currents and optimize the flow of shipping in a busy port.
An ADCP can also be an acoustic Doppler Velocity Log (DVL) if it is programmed with the correct signal processing logic. The DVL bounces sound off the bottom (or a reference layer of water) and can determine the velocity vector of a subsea vehicle (or surface vessel) moving across the sea floor. This information can be combined with a starting fix
Position fixing
Position fixing is the branch of navigation concerned with the use of a variety of visual and electronic methods to determine the position of a ship, aircraft or person on the surface of the Earth.These techniques include:...
, compass heading, and acceleration sensors (typically by use of a Kalman Filter
Kalman filter
In statistics, the Kalman filter is a mathematical method named after Rudolf E. Kálmán. Its purpose is to use measurements observed over time, containing noise and other inaccuracies, and produce values that tend to be closer to the true values of the measurements and their associated calculated...
) to calculate the position of the vehicle. DVLs are used to help navigate surface vessels, submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
s, autonomous underwater vehicle
Autonomous Underwater Vehicle
An autonomous underwater vehicle is a robot which travels underwater without requiring input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes non-autonomous remotely operated underwater vehicles...
s, and ROV
Rov
Rov is a Talmudic concept which means the majority.It is based on the passage in Exodus 23;2: "after the majority to wrest" , which in Rabbinic interpretation means, that you shall accept things as the majority....
s for precise positioning in an environment where GPS, and other navigational aids, don't work.