Multifan survey system and method

1. Multifan equipment for survey operations such as bathymetry, water column monitoring, forward look sonar, Doppler velocimetry, Doppler current profiling, and motion stabilization, the multifan equipment comprising:

a transmitter and a receiver of a multibeam echo sounder;

the transmitter for constructing a message that includes N>=3 coded message components to excite projectors in a single projector array;

each message component resulting in a particular projector array beam that ensonifies reflectors in a respective fan; and,

following transmission of a message, the receiver for receiving ensonified reflector returns via hydrophones arranged in a single hydrophone array;

wherein multiple hydrophone beams formed by the hydrophone array intersect the fans and fans are distinguished from each other using N filters.

2. The multifan equipment of claim 1 wherein the N filters are matched filters.

3. The multifan equipment of claim 1 wherein the N filters are band-pass filters.

4. The multifan equipment of claim 1 wherein each of the N filters includes a matched filter and a band-pass filter.

5. The multifan equipment of claim 1 wherein the projector array and the hydrophone array are linear arrays.

6. The multifan equipment of claim 1 wherein two projector arrays in a dual head configuration form the projector array and two hydrophone arrays in a dual head configuration form the hydrophone array.

7. The multifan equipment of claim 1 wherein:

each of the N message components is processed in a respective transmit beamformer;

signals derived from beamformer output are summed in a summation block; and,

signals derived from the summation block outputs drive respective projectors in the projector array.

8. The multifan equipment of claim 1 wherein:

parallel hardware pipelines in the receiver precede parallel software pipelines in the receiver;

the hardware pipelines process T signals from T hydrophones;

the software pipelines process input signals derived from the hardware pipeline outputs;

in the software pipelines, each of the input signals results in output signals for each of N fans; and,

N receiver beamformers, each beamformer driven by software pipeline outputs for a particular fan.

9. The multifan equipment of claim 8 wherein the T software pipelines include N processing strings per pipeline and each processing string in the software pipeline is for processing a signal related to a respective fan.

10. The multifan equipment of claim 1 wherein message components are derived from spread spectrum signals.

11. The multifan equipment of claim 1 wherein frequency hopping codes guide the selection of three or more frequencies characterizing each message component.

12. The multifan equipment of claim 11 wherein Costas codes guide the selection of frequencies.

13. The multifan equipment of claim 1 wherein message components are transmitted with temporal overlap.

14. The multifan equipment of claim 1 wherein message components are derived from FM signals.

15. The multifan equipment of claim 14 wherein two message components are derived from oppositely signed variations in the instantaneous frequency of two FM signals sharing a common frequency band.

16. The multifan equipment of claim 1 wherein message components are derived from CW signals with differing center frequencies.

17. A multifan survey method comprising the steps of:

constructing a message with N>=3 message components for ensonifying reflectors in N elongated fans, each message component distinguished from other message components by a code;

processing each message component in a respective transmit beamformer;

driving each of plural projectors with signals derived from all of the beamformers;

transmitting N beams from the projectors, each beam ensonifying reflectors in a respective one of the elongated fans;

forming multiple receive beams with each of N receive beamformers, the beams intersecting the elongated fans;

receiving returns from the reflectors via the receive beams; and,

acquiring survey data at multiple ones of the intersections, the data at each such intersection associated with a particular fan via the message component code.

18. The method of claim 17 wherein message components are transmitted with temporal overlap.

19. The method of claim 17 wherein message components are derived from FM signals.

20. The method of claim 17 wherein two message components are derived from oppositely signed variations in the instantaneous frequency of two FM signals sharing a common frequency band.

21. The method of claim 17 wherein message components are derived from CW signals with differing center frequencies.