Application of chirp sonar acoustic reflection coefficient for sea floor sediment classification: Results from the Delaware Estuary

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. Although 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 a relationship for the bottom sediments of the upper Delaware Estuary. The failure of the study to establish a relationship suggests that full spectrum chirp sonar has a limited capacity for acoustic classification of bottom sediment in the study area, and that more precise and higher resolution methods of data collection and processing may be necessary in order to address the heterogeneity as well as depositional complexity of sea floor sediments in estuarine environments.