We introduce a new technique to measure profiles of each term in the Reynolds stress tensor using coupled acoustic Doppler current profilers (ADCPs). The technique is based on the variance method which is extended to the case with eight acoustic beams. Methods to analyze turbulence from a single ADCP rely on questionable assumptions on turbulence anisotropy ratios and on the requirement of perfect vertical alignment, which are no longer necessary with the coupled system. We apply the technique successfully to data collected in the Mahakam River, East Kalimantan, Indonesia. Citation: Vermeulen, B., A. J. F. Hoitink, and M. G. Sassi (2011), Coupled ADCPs can yield complete Reynolds stress tensor profiles in geophysical surface flows, Geophys. Res. Lett., 38, L06406, doi:10.1029/2011GL046684
Turbulence strongly controls the exchange of momentum, heat and suspended or dissolved matter in geophysical surface flows occurring in rivers, estuaries and the coastal ocean. In fluvial systems turbulence generates secondary currents both in straight channels [e.g., Colombini, 1993; Blanckaert et al., 2010] and curved channels [e.g., Blanckaert and de Vriend, 2005], and controls shear layers at river confluences [Rhoads and Sukhodolov, 2004], at the interface between a floodplain and a main channel [Tominaga and Nezu, 1991], and within floodplains that feature roughness heterogeneity [Vermaas et al., 2011]. Field studies of river turbulence generally focus on small streams [Sukhodolov et al., 1998] where measurements at a high temporal and spatial resolution can be attained with a single point flow meter deployed at various positions in a frame. In estuaries and in the coastal ocean, turbulent fluxes are typically measured from a ship or from a bottom mounted rig [Smith et al., 2005; Mohrholz et al., 2008; Lueck et al., 2002]. Especially in studies in larger scale systems, acoustic Doppler current profilers (ADCPs) offer a promising alternative to measure turbulent quantities [Stacey et al., 1999a; Wiles et al., 2006].