Ambiguity resolution using dual frequency transducer for acoustic Doppler current profiler applications

Abstract

Broad Band Acoustic Doppler Current Profilers (ADCPs) have been used for over past 20 years to measure the relative velocity measurements in rivers and ocean environments but are inherently subjected to velocity ambiguities due to the phase change in the binary phase shift code. A new dual frequency transducer capable of transmitting and receiving at two different frequencies and having the same beam width is described here and is shown to resolve the inherent velocity ambiguity, thereby having velocity measurements with high accuracy and profile longer ranges from a single instrument. The electro-acoustic transducer made out of a piezoceramic in the shape of disc, vibrating in the extensional mode of operation is used in this approach to generate the directional acoustic radiation in the direction normal to the face of the transducer. The dual frequency transducer was integrated with the new generation ADCP-3 electronics, to transmit and receive sound underwater. An experimental investigation was conducted off San Diego coast using the dual frequency transducer operating at 2 different frequencies namely the low frequency at 300 kHz and high frequency at 1200 kHz in a single instrument and results are presented as a function of range and velocity measurements.