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. 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;
the received message reflections from locations where beams projected by the projectors intersect beams received by the hydrophones; 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 X is 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).