Acoustic doppler system and method
A survey system including a multibeam echo sounder having a projector array and a hydrophone array in a Mills Cross arrangement uses a multicomponent message to ensonify one or more fans to estimate a Doppler velocity.
1. An underwater acoustic system for estimating current flow, the system comprising:
a stationary multibeam echo sounder in a water column;
an acoustic transceiver for communicating with plural transducers in a single linear projector array and plural transducers in a single linear hydrophone array;
the projector array configured orthogonally with respect to the hydrophone array to form a Mills cross such that multiple projector array transmit fans and multiple hydrophone array receive beams intersect;
the acoustic transceiver for synthesizing a transmitter message and exciting the projector array such that multiple fans ensonify the water column;
the message including at least one pulse pair for each fan;
the hydrophone array for receiving transmitter message echoes from scattering centers entrained in the water column;
message echoes time-gated to associate with range cells along each beam of each fan; and,
a receiver for processing associated return signals via autocorrelation of pulse pairs to calculate a radial velocity for each range cell of each beam of each fan.
2. The underwater acoustic system of claim 1 wherein simultaneous consideration of a plurality of the radial velocity estimates provides an estimated velocity of the water column at one or more depths.
3. The underwater acoustic system of claim 2 wherein the radial velocities are Doppler radial velocities.
4. The underwater acoustic system of claim 3 where the number of fans is greater than or equal to 2.
5. The underwater acoustic system of claim 4 where the number of beams is greater than or equal to 8.
6. The underwater acoustic system of claim 2 wherein the transmitted message includes Barker codes.
7. The underwater acoustic system of claim 2 wherein the transmitted message includes orthogonal spread spectrum codes.
8. The underwater acoustic system of claim 2 wherein the multibeam echosounder distinguishes between echoes returned from each of the fans through temporal separation techniques.
9. The underwater acoustic system of claim 2 wherein the multibeam echosounder distinguishes between echoes returned from each of the fans through frequency separation techniques.
10. The underwater acoustic system of claim 2 wherein the multibeam echosounder distinguishes between echoes returned from each of the fans through code separation techniques.
11. The underwater acoustic system of claim 2 wherein at least one of the radial velocity estimates is estimated via minimization of a cost equation.