Broadband acoustic doppler current profiler

A method of deriving a measure of the relative velocity of a signal source-sensor combination and a field of scatterers separated therefrom by a medium through which the signal is propagated, wherein the source-sensor combination includes a transducer, the method comprising the steps of:

• energizing the transducer to emit into the medium towards the field of scatterers a signal comprising a plurality of pulses having a predetermined separation, wherein the pulses include at least a first and second pulse;
• sensing a signal comprising a set of echo returns of the pulses reflected from the field of scatterers;
• complex sampling the echo return signal at preselected sampling intervals so as to provide a first set of complex samples;
• delaying the first set of complex samples by a predetermined lag time so as to provide a second set of complex samples;
• presenting to a complex correlator the first and second sets of samples wherein the first set consists primarily of echoes from the first pulse and the second set consisting primarily of echoes from the second pulse, and forming as outputs the complex products of members of the first set with complex conjugates of members of the second set, to produce a complex correlation value;
• and
• obtaining a Doppler frequency based on the phase change calculated from the complex correlation value.

A current profiler, comprising:

• a transducer for transmitting and a transducer for receiving an acoustic signal having first and second coded pulses separated by a preselected lag time wherein the coded pulses are in water together for at least a portion of a selected time interval;
• a sampler for sampling quadrature components of a received signal over a time interval which depends on the selected range cell, wherein the received signal comprises echoes of the coded pulses;
• means for calculating the autocorrelation of the sampled quadrature components;
• means for determining the Doppler frequency of the received signal comprising means for calculating the phase change of the acoustic signal from the autocorrelation result;
• and
• means for calculating a velocity using the Doppler frequency.

A Doppler sonar system for providing velocity measurements, comprising:

• a transducer;
• a pulse generator communicating to the transducer two or more coded pulses of preselected length separated by a preselected lag time;
• a complex sampling circuit connected to the transducer so as to provide quadrature components of a received echo signal;
• and
• a processor including autocorrelation means for generating the autocorrelation between a first set of quadrature samples and a second set of quadrature samples delayed by the lag time, the processor also including means for obtaining a velocity measurement based on a Doppler frequency calculated from the autocorrelation.