|
School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK (e-mail: c.vincent{at}uea.ac.uk)
Suspended sand concentrations in the near-bed layer of the sea can be estimated using acoustic backscatter systems (ABS) and hence, when combined with velocity, sand transport. ABS measurements are now relatively routine and widely regarded as one of the best tools to help to measure sand transport in coastal seas and estuaries. Potentially the ABS can be used to give estimates of both concentration and sediment size with a vertical resolution of 5–10 mm and a temporal resolution of fractions of a second, but in practice there are many practical limitations to what can be achieved in the field. Often these uncertainties are overlooked or ignored because of the difficulty in estimating their magnitude or of making measurements that are any better. The major limitations and sources of errors in the ABS are discussed, including the influence of sediment size and shape. In moderately to well-sorted sandy environments with appropriate calibration, acoustic estimates of mass concentration should be within ± 30% of the true value.
