What is the difference between ADCP velocity frames of reference?

ADCPs can produce water velocity measurements in any of four frames of reference: beam frame, instrument frame, vessel frame and earth frame. Understanding velocity frames of reference is important for data inspection/interpretation and for selecting the correct one for your application.

Beam Frame

Beam frame means water velocity along the direction of the beam (beam 1, beam 2, beam 3 …). These are raw measurements determined independently by each transducer.

Instrument Frame

Instrument frame means water velocity in a coordinate system relative to the device (X, Y, Z). The X, Y and Z axes are always orientated the same relative to the transducer head. When the X-Y plane is level, the internal compass measures the orientation of the Y-axis relative to magnetic north.

Vessel Frame

Vessel frame means water velocity with respect to the vessel (starboard, forward, up/mast – axes that are more commonly known as pitch, roll and yaw).

Earth Frame

Earth frame means water velocity with respect to Earth (east, north, up), i.e. true orientations. This is a stable frame of reference for ensemble averaging and therefore the most commonly used.

For Origin ADCPs using Origin Viewer you can swap between different frames of reference.

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