The beam velocities along the four beams are combined to find 3D-velocity vectors, these 3D-vectors are transformed to vessel
coordinates, and the result is the Vessel velocity.
Using data from GPS and motion sensors, vessel velocity values are recalculated into global coordinate
oriented values and the velocity of the vessel is removed. The result is the global current velocity
values, velocites in north-south and east-west direction.
Velocity data
Velocity data are output in units of m/s or knots.
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Beam velocity Beam velocity is the relative velocity between sea and transducer measured in the beam direction. The relative velocity between
the sea and transducer will have a component along the beam direction. This component is measured in the beam velocity.The Beam Velocity views offers one presentation for each beam. This velocity is often referred to as relative to beam coordinates.
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Vessel velocity Vessel velocity is 3D velocity found from the beam velocity and relative to the directions of the vessel, fore/aft, port/starboard.
The movements of the transducer is included in this velocity estimates. The Vessel Velocity views include one view for velocity in the fore/aft direction, one for port/starboard direction, one for speed (i.e. no direction
indicated) and one for up/downward velocity. This is often referred to as velocity relative to vessel coordinates.
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Geo velocity Geo velocity is current velocity estimated from the vessel velocity and relative to the cardinal directions, north/south east/west.
The movements of the transducer are removed from these estimates. The Geo Velocity views include one view for north/south direction, one for east/west direction one for current speed (i.e. no direction indicated)
and one for up/downward velocity of the current. This is often referred to as velocity relative to earth coordinates.
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Error velocity Error velocity is the difference between to estimates of vertical velocity. It is calculated using beam velocity data. The differences in vertical velocity estimates can be due to inhomogeneities in the water velocity, noise or malfunctioning
equipment.
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Correlation data
Correlation is a measure of similarity between the two sets of received echoes. The test is based on beam velocity echoes,
ie. velocity along the beam direction
If the difference is small, correlation is high and the signal sequences are similar. When Correlation is enabled, velocity estimates with correlation below the threshold value are edited out. This means these velocity estimates will not be shown in the velocity views and not included in ping average. Set the correlation threshold value to remove noisy measurements for correlations values lower than the threshold value.
Percent good data
The term percent good is commonly used to describe the total remaining value of an asset after a certain time compared to the value of the original
asset. The percent good fraction is calculated using the number of pings selected with the Ping Average function.
The Percent Good filter applies to the Vessel Velocity and Geo Velocity views.. The Beam Velocity views do not use this quality measurement.
It tells what fraction of pings passed both the error velocity and correlation threshold editing.
The percent good fraction is calculated using the number of pings selected with the Ping Average function. When calculating ping average, only the velocities which have passed the error velocity and correlation editing are included. The percent good threshold sets the lower limit for what fraction of pings must have passed the other threshold edits. Averaged velocities, ADCP data, with percent good below this limit are not shown in the velocity views.
Backscatter data
The ADCP is designed to measure currents, but it can also be a useful tool for investigating the distribution and abundance
of zooplankton in the water. Backscatter views are displayed with a true depth scale. (Compensating for the 30deg steering of the beams).The intensity of the backscattered soundwaves for each depth cell is a “snapshot” of the echo intensity at a distance of two-thirds
the way along the depth cell. This can be used to estimate the integrated mass of the backstterers over the footprint volume (width and thickness) of the
original acoustic beams.