To measure sediment concentration, two acoustic backscattering systems and optical backscattering sensors are used. An indirect measurement of the particle size distribution can be obtained from inverting the acoustic and optical backscattering measurements with respect to size/wavelength dependent scattering strengths. A direct measurement of the size dependence of the suspended sediment concentration is obtained from the Laser In-Situ Sizing and Transmissometery (LISST) instrument developed by Y. Agrawal at Sequoia Scientific. Transport of sediment is also not measured directly but calculated from water velocities as measured by ElectroMagnetic Current Meters (EMCM’s), and the Benthic Acoustic Stress Sensor (BASS). These water velocity measurements are also needed as forcing parameters for the suspension modelling. Another important measurement in sediment transport is the bottom roughness. To measure roughness both the acoustic backscattering systems, which serve as altimeters, and a rotary Sector Scanning side scan Sonar system (SSS) are used. Since both wave and current action are important in resuspending and transporting sediment, the time sampling of most of the instruments are designed to sample both the faster wave period time scale and the slower current time scales. To do this the instruments are typically run at a fast (0.25 - 1 Hz) sampling rate for several (4-8) minutes to capture the waves and wave groups. These bursts are repeated every hour or half hour to monitor the slower scale processes. This conserves battery power and memory to allow for deployment lengths of several months.
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