BB 150 ADCP Technical Manual
The ADCP emits an acoustic pulse called a PING. Scatterers that float ambiently with the water currents reflect some of the energy from the ping back to the ADCP. The ADCP uses the return signal to calculate a velocity. The energy in this signal is the echo intensity. Echo intensity is sometimes used to determine information about the scatterers.
The velocity calculated from each ping has a statistical uncertainty; however, each ping is an independent sample. The ADCP reduces this statistical uncertainty by averaging a collection of pings. A collection of pings averaged together is an ensemble. The ADCP’s maximum ping rate limits the time required to reduce the statistical uncertainty to acceptable levels.
The ADCP does not measure velocity at a single point; it measures velocities throughout the water column. The ADCP measures velocities from its transducer head to a specified range and divides this range into uniform segments called depth cells (or bins). The collection of depth cells yields a profile. The ADCP produces two profiles, one for velocity and one for echo intensity.
The ADCP calculates velocity data relative to the ADCP. The velocity data has both speed and direction information. If the ADCP is moving, and is within range of the bottom, it can obtain a velocity from returns off the bottom. This is called bottom-tracking. The bottom-track information can be used to calculate the absolute velocity of the water. The ADCP can get absolute direction information from a heading sensor.
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