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 acoustic Doppler sonar system for estimating relative velocities comprising:
plural transducers in a single projector array provide an acoustic source;
a transmitter for exciting the projector array;
the excited projector array for ensonifying reflectors in each of multiple underwater fans;
plural transducers in a single hydrophone array for sensing backscattered returns from the reflectors;
a receiver for processing the backscattered returns; and,
the arrays configured with respect to each other such that multiple hydrophone beams intersect the fans;
wherein the Doppler system utilizes
a transmitter message for ensonifying i>=2 fans, the message including at least one pulse pair per fan,
j>=2 hydrophone beams per fan, and
hydrophone returns processed to calculate for each of (i*j) beams respective Doppler radial velocity estimates DRVi,j such that simultaneous consideration of the DRVi,j provides an estimated relative velocity.
2. The acoustic Doppler sonar system of claim 1 wherein the processing of backscattered returns includes autocorrelation of pulse pairs.
3. The acoustic Doppler sonar system of claim 2 wherein the estimated relative velocity is a Doppler radial velocity.
4. The acoustic Doppler sonar system of claim 1 wherein each fan occupies a unique frequency band that enables one fan to be distinguished from other fans.
5. The acoustic Doppler sonar system of claim 4 does not distinguish among signals using matched filtering.
6. The acoustic Doppler sonar system of claim 5 wherein pulses use Barker or orthogonal spread spectrum codes to ensonify the fans.
7. The acoustic Doppler sonar system of claim 1 wherein each fan occupies a unique temporal window that enables one fan to be distinguished from other fans.
8. The acoustic Doppler sonar system of claim 7 does not distinguish among signals using matched filtering.
9. The acoustic Doppler sonar system of claim 8 wherein pulses use Barker or orthogonal spread spectrum codes to ensonify the fans.
10. The acoustic Doppler sonar system of claim 1 wherein relative velocity is estimated using a cost minimization equation.
11. The acoustic Doppler sonar system of claim 1 wherein the projector array and the hydrophone array are linear arrays.
12. The acoustic Doppler sonar system of claim 1 wherein the message is a serial-serial message for sequentially ensonifying each of the i fans wherein:
the fans are ensonified serially;
for each fan, the 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.
13. The acoustic Doppler sonar system of claim 1 wherein the message is a serial-parallel message for ensonifying fans wherein:
the fans are ensonified simultaneously;
for each fan, the 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.
14. The acoustic Doppler sonar system of claim 1 wherein the fans are ensonified simultaneously and separable via frequency band.
15. The acoustic Doppler sonar system of claim 14 wherein each pulse includes a Barker code or an orthogonal spread spectrum code.
16. The acoustic Doppler sonar system of claim 14 wherein:
the arrays are installed on a vessel;
for each beam, an autocorrelation magnitude value is used to identify a waterbody bottom range cell; and,
a Doppler velocity log (DVL) bottom tracking mode of operation provides an estimate of vessel velocity relative to a waterbody bottom.
17. The acoustic Doppler sonar system of claim 14 wherein:
the arrays are installed on a vessel;
for each beam, a water column range cell of interest is selected; and,
a Doppler velocity log (DVL) water tracking mode of operation provides an estimate of projector array velocity relative to a layer of water in the water column at the range cell of interest.
18. The acoustic Doppler sonar system of claim 14 wherein:
the arrays are stationary;
for each beam, a water column range cell of interest is selected; and,
an acoustic Doppler current profile (ADCP) mode of operation provides an estimate of water current velocity.
19. The acoustic Doppler sonar system of claim 14 wherein message components include 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 and (ys*yb)>(xs*xb).
20. The acoustic Doppler sonar system of claim 1 wherein the fans are ensonified sequentially and separable via frequency band.
21. The acoustic Doppler sonar system of claim 20 wherein each pulse includes a Barker code or an orthogonal spread spectrum code.
22. The acoustic Doppler sonar system of claim 20 wherein:
the arrays are installed on a vessel;
for each beam, an autocorrelation magnitude value is used to identify a waterbody bottom range cell; and,
a Doppler velocity log (DVL) bottom tracking mode of operation provides an estimate of vessel velocity relative to a waterbody bottom.
23. The acoustic Doppler sonar system of claim 20 wherein:
the arrays are installed on a vessel;
for each beam, a water column range cell of interest is selected; and,
a Doppler velocity log (DVL) water tracking mode of operation provides an estimate of projector array velocity relative to a layer of water in the water column at the range cell of interest.
24. The acoustic Doppler sonar system of claim 20 wherein:
the arrays are stationary;
for each beam, a water column range cell of interest is selected; and,
an acoustic Doppler current profile (ADCP) mode of operation provides an estimate of water current velocity.
25. The acoustic Doppler sonar system of claim 20 wherein message components include 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 and (ys*yb)>(xs*xb).