U.S. Geological Survey Open-File Report 2007-1194
Figure 10. An upward-looking Acoustic Doppler Current Profiler (ADCP) mounted on a corner of a small tripod frame. The ADCP head, composed of four transducers (red circles in the photograph), transmits acoustic pulses along two pairs of orthogonal beams (four beams total). Pulses reflected from scatterers in the water column are received by the ADCP and converted into eastward, northward, and vertical components of water flow using the Doppler shift and basic trigonometry.