THE CAPACITY OF CHIRP SONAR FOR REMOTE CLASSIFICATION OF BENTHIC SEDIMENTS IN AN ESTUARINE ENVIRONMENT

Sea floor acoustic reflectivity values, collected in the upper Delaware Estuary, are correlated with coincident benthic sediment samples in order to evaluate the capacity of full spectrum chirp sonar for bottom sediment classification in estuarine environments. Physical properties of the sea floor sediments including sorting, porosity, and grain size distribution were determined through sieve, pipette, and gravimetric analysis, of 55 Smith-McIntyre grab samples and 5 hydraulically dampened cores. Resultant values were correlated with coincident measurements of sea floor reflection coefficient, collected with a full spectrum 2-12 kHz chirp sonar, which indicate the acoustic reflectivity of the sediment water interface. Sediment reflectivity values were plotted as a function of grain size, porosity, and sediment classification in order to graphically define a relationship between the acoustic and physical properties of the sea floor in the study area. While previously published results of laboratory as well as field experiments indicate a positive relationship between sediment reflection coefficient values and porosity as well as sediment reflection coefficient values and mean grain size, the results of this study failed to demonstrate an analogous relationship for the bottom sediments of the upper Delaware Estuary. The failure of the results to establish such a relationship is attributable to insufficient methodological precision exacerbated by the heterogeneity as well as depositional complexity of the estuarine environment, rather that the capacity of the chirp sonar, which demonstrated high instrumental precision. The results suggest that the chirp sonar has the potential to accurately classify estuarine sediments and indicate a number of methodological and environmental considerations that must be addressed in order realize that potential.