System and method for acoustic doppler velocity processing with a phased array transducer including using differently coded transmit pulses in each beam so that the cross-coupled side lobe error is removed
View Patent ↗A system and method for measuring velocity in a fluid medium utilizing a transducer are disclosed. In one aspect, the method comprises transmitting an acoustic signal comprising N (where N is integer and N>1) pings for each of a plurality of beams, receiving echoes from each ping, obtaining a velocity estimate for each of the N pings based on echoes of the ping, and calculating a velocity based on the sum of the N velocity estimates such that the velocity is substantially free from error caused by cross-coupling between the beams.
1. A system configured to measure velocity, comprising:
a transducer for transmitting an acoustic signal comprising N (N is integer and N>1) pings for each of a plurality of beams and receiving echoes from each ping; and
a processing module configured to obtain a velocity estimate for each of the N pings based on echoes of the ping and to calculate a velocity based on a the sum of the N velocity estimates to substantially remove error caused by cross-coupling between the beams.
2. A system configured to measure velocity, comprising:
means for transmitting an acoustic signal comprising N (where N is integer and N>1) pings for each of a plurality of beams;
means for receiving echoes from each ping;
means for obtaining a velocity estimate for each of the N pings based on echoes of the ping; and
means for calculating a velocity based on a the sum of the N velocity estimates such that the velocity is substantially free from error caused by cross-coupling between the beams.
3. The system of claim 1 , wherein the transducer is configured to simultaneously transmit a first acoustic signal comprising N pings for a first beam and a second acoustic signal comprising N pings for a second beam, wherein the first acoustic signal is different from the second acoustic signal.
4. The system of claim 3 , wherein each of the first acoustic signal and the second acoustic signal comprises a plurality of code elements, each code element comprising a particular phase shift, wherein at least one code element of the first acoustic signal has a phase shift different from a code element of the second acoustic signal transmitted at the same time.
5. The system of claim 1 , wherein each of the N velocity estimates is obtained based on echoes of the beams corresponding to one of the N pings.
6. The system of claim 2 , wherein the transmitting means further comprises means for simultaneously transmitting a first acoustic signal comprising N pings for a first beam and a second acoustic signal comprising N pings for a second beam, wherein the first acoustic signal is different from the second acoustic signal.
7. The system of claim 6 , wherein each of the first acoustic signal and the second acoustic signal comprises a plurality of code elements, each code element comprising a particular phase shift, wherein at least one code element of the first acoustic signal has a phase shift different from a code element of the second acoustic signal transmitted at the same time.
8. The system of claim 2 , wherein each of the N velocity estimates is obtained based on echoes of the beams corresponding to one of the N pings.
9. The system of claim 2 , wherein the transmitting means comprises a transducer.
10. The system of claim 2 , wherein the transmitting means comprises a plurality of piston transducers.
11. The system of claim 2 , wherein the transmitting means comprises a phased array transducer, the phased array transducer comprising a plurality of transducer elements arranged to form a single two-dimensional array.
12. The system of claim 1 , wherein the transducer comprises a plurality of piston transducers.
13. The system of claim 1 , wherein the transducer comprises a phased array transducer, the phased array transducer comprising a plurality of transducer elements arranged to form a single two-dimensional array.
14. The system of claim 13 , wherein the phased array transducer is configured to form at least a first plane of beams and a second plane of beams, wherein the transmitted signals are selected such that, for each pair of beams generated within the same plane, the sum of N cross-coupling factors between the pair is substantially 0, wherein each cross-coupling factor corresponds to one ping.
15. The system of claim 1 , wherein the measured velocity is the velocity of currents in the fluid medium.
16. The system of claim 1 , wherein the measured velocity is the velocity of a vehicle or vessel relative to the bottom or surface of the fluid medium.
17. The system of claim 1 , wherein the measured velocity is the velocity of a target.
18. The system of claim 1 , wherein the transmitted signals are selected such that, for each pair of beams, the sum of N cross-coupling factors between the pair is substantially 0, wherein each cross-coupling factor corresponds to one ping.
19. The system of claim 1 , wherein the plurality of beams comprises at least 4 beams, and wherein N is an integer no less than 4, wherein the transmitted signal comprises a signal shown in the table below:
Ping
Beam 1
Beam 2
Beam 3
Beam 4
1
0° Two-Tone I
0° Two-Tone II
0° Two-Tone I
0° Two-Tone II
2
+90° Quint I
−90° Quint I
+90° Quint I
−90° Quint I
3
180° Barker I
180° Barker II
0° Two-Tone I
0° Two-Tone II
4
−90° Quint I
+90° Quint II
+90° Quint I
−90° Quint II.
20. The system of claim 19 , wherein the transducer comprises a phased array transducer configured to generate a first and second plane of beams, wherein one of the planes comprises beam 1 and 2 and the other of the planes comprises beam 3 and 4 .