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 multi-component message to ensonify one or more fans to estimate a Doppler velocity.
1. An underwater acoustic Doppler system for estimating a relative velocity, the system comprising:
a transmitter for transmitting a message for ensonifying i>=2 fans, the message including at least one pulse pair for each fan, and each fan including j>=8 beams;
a receiver for receiving message reflections, the transmitting and receiving utilizing transducers in projector and hydrophone arrays;
plural ones of the plurality of transducers for forming a Mills Cross; and,
the pulse pairs for making Doppler velocity estimates.
2. The system of claim 1 wherein:
the reflections are processed via auto correlation of pulse pairs to calculate for each of (i*j) beams respective Doppler radial velocity estimates DRVi,j.
3. The system of claim 2 wherein:
consideration of a plurality of the DRVi,j estimates provides an estimated source velocity.
4. The system of claim 2 wherein:
simultaneous consideration of a plurality of the DRVi,j estimates provides an estimated source velocity.
5. 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.
6. The system of claim 5 exclusive of matched filtering.
7. The system of claim 6 wherein each pulse uses a Barker code.
8. The system of claim 5 further comprising:
a digital processing section of the receiver; and,
wherein a source velocity estimate uses quantity r1<(i*j) of Doppler radial velocity estimates DRVi,j and r1 is determined in part by digital processing section processing capacity.
9. The system of claim 1 further 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.
10. The system of claim 9 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.
11. The system of claim 10 wherein pulse Xis a short pulse with a transmission time timex and pulse Y is a long pulse with a transmission time timey>timex.
12. The system of claim 11 wherein (ys*yb)>(xs*xb).
13. A method of making velocity estimates by operating an underwater acoustic Doppler system, the method comprising the steps of:
constructing a multibeam echo sounder message for transmission from a source moving at Vsource relative to a waterbody bottom;
with a message, ensonifying each of i>=2 fans with j>=8 beams;
processing returns to determine (i*j) Doppler radial velocities DRVi,j; and,
determining from DRVi,j and other knowns a velocity vector representative of velocity vector Vsource.
14. The method of claim 13 exclusive of matched filtering.
15. The method of claim 14 wherein the message includes at least one pulse pair for each fan.
16. The method of claim 15 wherein return signals are processed via auto correlation of pulse pairs to calculate for each of (i*j) beams respective Doppler radial velocity estimates DRVi,j.
17. The method of claim 16 wherein consideration of a plurality of DRVi,j estimates provides an estimated source velocity.
18. The method of claim 16 wherein simultaneous consideration of a plurality of DRVi,j estimates provides an estimated source velocity.
19. The method of claim 16 wherein DRVi,j, beam projection angle, and fan angle are known values.
20. The method of claim 19 wherein each of Vsource=Relative velocity between the projector array and reflector, yaw angle, and pitch angle are unknown values.