U.S. Geological Survey Open-File Report 2007-1194
Figure 12. A SonTek Argonaut-XR (Extended Range) Acoustic Doppler Profiler (ADP) mounted on a small tripod in upward-looking configuration. The ADP's transducers (at top right of image) transmit and receive sound along acoustic beams. Because Doppler shift is proportional to the component of water is flow along the beams, trigonometry can be used to convert the returned acoustic signal into eastward, northward, and vertical components of water flow.