Examples of Near Bottom Velocity Data and Residual Velocity Data Collected by ADCP

The acoustic Doppler current profiler (ADCP) is an instrument that transmits and receives acoustic energy to measure water motion by utelizing the Doppler effect when analyzing echos returned by scatterers in the water. This image displays tidal velocities in the bottom boundary layer from very near bottom to about 1.5 meters above bed. The ADCP is operating in a high resolution mode that can determine velocity profiles with 5 cm resolution. This "snapshot" was taken near maximum flood tide (the instrument was moored near the San Mateo Bridge in South San Francisco Bay).

This image shows residual velocities measured by ADCP moored in Carquinez Strait. The measured velocities have been filtered to remove the tidal components leaving the net (residual) velocity. Note that the net flow is up estuary (to the right) near bottom and down estuary (to the left) near surface. This "snapshot" was near neap tides as seen in the time series of water surface elevation in the upper portion of the image. The velocity vectors are spaced at 1 meter apart.