U.S. Geological Survey Open-File Report 2007-1194
Figure 16. SonTek IQ (right) and YSI 6600 sonde as deployed on a grate platform in the Rachel Carson National Wildlife refuge in 2013. The IQ measures along and across channel water flow from the Doppler shift that occurs when scatterers carried by the water reflect paired acoustic pulses. The IQ uses 5 acoustic beams to characterize flow rate and water level using vertical bins as small as 2cm.