Evaluating Methods For Correcting Acoustic Backscatter Data Used In Suspended-Sediment Computations Due To Fouling Attenuation

The sediment acoustic index method is a standard technique for computing suspended-sediment concentrations from acoustic indices derived from acoustic Doppler velocity meter (ADVM) backscatter data. As the sediment acoustic index method gains more widespread use in the scientific community, the range of aquatic environments in which it will be used will increase. In some environments, such as coastal watersheds, heavy biofouling has the potential to substantially affect the quality of the backscatter signal, thus reducing the accuracy of the continuous time-series of computed suspended-sediment concentrations. The need to correct backscatter data has been suggested to address signal attenuation caused by biofouling; however, guidelines on methods, and best practices of applying corrections to backscatter data have not been developed. Data from U.S. Geological Survey (USGS) streamgages along the Texas Gulf Coast were used to develop and evaluate a method for correcting acoustic backscatter data that reduces the adverse effects of biofouling on suspended-sediment concentration computations when using ADVMs. A method for correcting acoustic backscatter data affected by biofouling was developed by (1) evaluating the potential methods for correcting acoustic backscatter data affected by biofouling and determining the most appropriate acoustic backscatter dataset to apply corrections to; (2) reviewing the correction methods for ease of implementation and applicability to multiple locations; (3) assessing the effects of correcting data on surrogate model quality by comparing models developed with raw data and models developed with corrected data; and (4) developing recommendations on correction methods, criteria and limits, documentation processes, and implementation in the current USGS Aquarius platform. Developing standard methods for documenting and addressing attenuated acoustic backscatter data in environments in which heavy biofouling occurs is essential to maintaining accurate, consistent, and comparable suspended-sediment estimates derived from acoustic index equations.