Abstract
Laboratory experiments were conducted to compare the performances of four different instruments for measuring suspended cohesive sediment concentrations (SSCs). Among these instruments, two were different models of optical backscatter sensor (i.e., OBS3+ and OBS5+), one was an acoustic Doppler velocimeter (MicroADV), and the last was a laser infrared optical sensor developed at Hohai University, China (HHU-LIOS). Sediments collected from the Yangtze River Estuary and a commercially available kaolinite were selected to check the responses of these four instruments. They were placed in an aqueous solution, and the SSCs were changed within a range from about 10 mg/L to 30 g/L to demonstrate the effective measuring ranges for each instrument. For the kaolinite suspension, the results showed that the HHU-LIOS has a much larger linear response range (0.1 to 13 g/L) when compared with other devices (the MicroADV: 0.1 to 1.35 g/L; the OBS3+: 0.1 to 5 g/L; and the OBS5+: 0.1 to 1 g/L). For the sediment sample from the Yangtze River Estuary, the results showed that the HHU-LIOS has a much wider usable range (from 0.1 to 25 g/L), compared with those for the others. It also showed that a combination of using a HHU-LIOS for the quadratic increasing range up to 25 g/L and the OBS5+ for the clear decreasing output are able to measure the SSCs of the estuarine mud up to 50 g/L.
Highlights
Suspended sediment concentration (SSC) in river, estuary, and coastal waters is an important factor to better understand sediment transport processes, e.g., flocculation [1], settling [2], erosion [3], and deposition
Water samples were taken from two outlets located at 8 and 23 cm above the bed, respectively, for getting the ground-truth SSC in order to calibrate the responses of all the instruments
The analog output signals from the OBS3+ and HHU-LIOS were sent to an analog-to-digital conversion card and the digitized data were stored in a computer for later processing
Summary
Suspended sediment concentration (SSC) in river, estuary, and coastal waters is an important factor to better understand sediment transport processes, e.g., flocculation [1], settling [2], erosion [3], and deposition. The early approach was limited to taking water samples back to a laboratory, measuring the water volume and sediment mass. This is still the basic approach, and the measurement results may be claimed as a ground truth even today. This approach suggested that only time-averaged measurements at a specific point (or within a small volume) are possible. Techniques of using acoustic waves contributed to save time and even possibly to measure SSC profiles [6]. The possible linear measurement range is still limited to less than around 1 g/L for cohesive sediments
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