Bottomtrack

Bottomtrack is a mode used in acoustic Doppler current profiler (ADCP) systems to determine the instrument’s motion relative to the seabed by tracking the bottom echo. When the seabed within the acoustic range provides a strong and stable reflection, the ADCP can estimate its velocity relative to the bottom from the Doppler shift of the bottom return. This bottom-referenced velocity serves as a reference frame for the current measurements.

In practice, bottomtrack uses the Doppler shifts from returns off the seabed to derive the instrument’s along-track, cross-track, and vertical velocities with respect to the bottom. The bottom-track data are often used to correct or complement the water-column velocity measurements, enabling the computation of earth-referenced current velocities by accounting for ship or platform motion, tilt, and GPS-derived position as needed. Bottomtrack is commonly available on hull-mounted, vessel-mounted, and some moored or autonomous deployments when a reliable bottom echo is present.

Bottomtrack quality depends on factors such as depth, bottom reflectivity, seabed roughness, and instrument height above the bottom. If the bottom is too deep, soft, or poorly reflective, bottomtrack may be weak or unavailable, in which case water-column (or “water-track”) measurements are relied upon. Data products typically include indicators of bottomtrack availability and quality, such as velocity estimates and confidence flags.

Overall, bottomtrack provides a stable reference for motion correction and improves the accuracy of ocean current measurements, particularly in moving-platform deployments and shallow to moderate-depth surveys.