A simple method for calibrating optical backscatter sensors in high concentrations of non-cohesive sediments

A new method is introduced for calibrating optical backscatter sensors for suspended quartz sand concentrations of up to 200 kg m(-3). Due to the high settling velocity of quartz sand in water, considerable difficulties have arisen in the past to maintain a spatially and temporally homogeneous suspension suitable for calibration. Traditional methods are clumsy and prone to errors. Here, the sediment is calibrated in glycerol, a clear fluid with a higher viscosity than water. The settling velocity is reduced by three orders of magnitude. An empirical relationship is obtained which is used to correct for any optical differences in response of the sensors in the two fluids. Any extra errors introduced by calibrating with a different fluid from that found in the field are outweighed by the simplicity and reliability of this method. (C) 2002 Elsevier Science B.V. All rights reserved.