Acoustic doppler system and method
A survey system including a multibeam echo sounder having a projector array and a hydrophone array uses a multi-component message to ensonify one or more fans to estimate a Doppler velocity.
1. A system for estimating water current flows, the system comprising:
a stationary multibeam echo sounder in a water column;
an acoustic transceiver of the echo sounder configured to communicate with a) plural transducers in one projector array and b) plural transducers in one hydrophone array;
the acoustic transceiver synthesizes one transmitter message and excites the projector array with the transmitter message such that multiple fans ensonify the water column;
the transmitter message includes at least one pulse pair for each fan; and,
the acoustic transceiver and hydrophone array form multiple hydrophone array receive beams and a plurality of hydrophone array receive beams intersect each fan;
wherein the hydrophone array receives transmitter message echoes from scattering centers entrained in the water column.
2. The system of claim 1 wherein message echoes are time-gated to associate with range cells along each beam of the fan.
3. The system of claim 2 wherein a receiver processes associated return signals via autocorrelation of pulse pairs to calculate a radial velocity for each range cell of each beam of each fan.
4. The system of claim 1 wherein there are i fans and j>=8 beams, echoes being processed via auto correlation of pulse pairs to calculate for each of (i*j) beams respective Doppler radial velocity estimates DRVi,j.
5. The system of claim 4 wherein evaluation of a plurality of the DRVi,j estimates provides an estimated source velocity.
6. The system of claim 4 wherein simultaneous evaluation of a plurality of the DRVi,j estimates provides an estimated source velocity.
7. The system of claim 1 wherein:
for each fan, ensonifying pulses are transmitted in a respective frequency band as pulses without temporal overlap; and,
the receiver for matching returns with fans based at least in part on frequencies of the returns.
8. The system of claim 7 exclusive of matched filtering.
9. The system of claim 8 wherein each pulse uses a Barker code.
10. The system of claim 1 wherein the message includes i) a pulse pair X-X where pulse X is an xb bit code with xs samples per bit and ii) a pulse pair Y-Y where pulse Y is a yb bit code with ys samples per bit.
11. The system of claim 10 wherein:
for each fan, ensonifying pulses are transmitted in a respective frequency band as serialized pulses without temporal overlap; and,
the receiver determines which returns come from which fans based at least in part on the frequencies of the returns.
12. The system of claim 11 wherein pulse X is a short pulse with a transmission time timex and pulse Y is a long pulse with a transmission time timey>timex.
13. The system of claim 12 wherein (ys*yb)>(xs*xb).
14. The system of claim 1 wherein relative velocity is estimated using a cost minimization equation.
15. The system of claim 1 wherein the projector array and the hydrophone array are linear arrays.
16. The system of claim 1 wherein the message is a serial-parallel message for simultaneously ensonifying the fans.
17. The system of claim 1 wherein the fans are ensonified simultaneously and separable via frequency band.
18. The system of claim 1 wherein the message is a serial-serial message for sequentially ensonifying each of the fans.