The short-period vertical motion of the vessel about its mean level, estimated by integrating accelerations in the motion sensor. Real-time heave relies on a filter that struggles with long-period swell and sharp turns, so many surveys apply delayed or post-processed heave instead. Uncorrected heave shows as ripples along track that mimic sand waves. Induced heave, from the lever arm between sensor and transducer during roll and pitch, must also be handled.
Heave's leaking through in this long swell, apply the delayed heave before you call those sand waves.
Long turns and speed changes upset real-time heave filters for a minute or more, one reason good lines have a generous run-in.
Also heard as
- vertical motion
Related terms
Roll
Rotation of a vessel about its fore-and-aft axis, measured to correct the angle of every sonar beam.
Pitch
Bow-up or bow-down rotation of a vessel, which shifts sonar footprints forward or aft along the track.
MRU
Motion reference unit: the sensor that measures a vessel's roll, pitch and heave to correct sonar data.
Bust
A vertical or horizontal mismatch between overlapping lines or surveys that exposes an error somewhere.
ERS
Ellipsoidally referenced survey: depths taken from GNSS ellipsoid heights and converted to chart datum with a separation model.