Multifan survey system and method

1. A survey system for performing a multifan bathymetric survey, the survey system comprising:

a multibeam echo sounder including a receiver and a transmitter for use with a plurality of transducers in a single projector array and a single hydrophone array;

the projector array and the hydrophone array for use in a Mills Cross arrangement;

the transmitter configured to generating a message including N>=3 coded message components that overlap in time and frequency;

the message for exciting each of the projectors in the projector array;

the message components configured to simultaneously ensonify three or more respective fans using the projector array;

the receiver for receiving returns from the ensonified fans via the hydrophone array; and,

N matched filters in the receiver, each matched filter configured to selectively detect a respective fan return out of the three or more respective fans.

2. The survey system of claim 1 wherein each of the message components occupies substantially all of a message frequency band.

3. The survey system of claim 1 further comprising:

N signal generators in the transmitter, each signal generator for generating a respective one of the coded message components.

4. The survey system of claim 1 further comprising:

N spread spectrum signal generators in the transmitter, each signal generator for generating a respective one of the coded message components; and,

wherein a message component frequency band occupies less than one-half of the receiver operating frequency range.

5. The survey system of claim 1 further comprising:

the message including M>=1 coded message components that do not overlap with the N message components.

6. The survey system of claim 1 further comprising:

N spread spectrum signal generators in the transmitter, each signal generator for generating a respective one of the coded message components; and,

wherein a message component frequency band occupies substantially all of the receiver operating frequency range.

7. The survey system of claim 6 further comprising:

a set of differing frequency hopping codes, each code used to guide a selection of three or more frequencies characterizing each message component.

8. The survey system of claim 7 wherein the message component includes sequential sinusoidal waveforms at the three or more frequencies.

9. The survey system of claim 8 wherein Costas codes are used to guide the selection of frequencies.

10. The survey system of claim 9 wherein the message components within the message are transmitted in parallel.

11. The survey system of claim 6 wherein the message includes five or more message components.

12. The survey system of claim 11 wherein the message components within a message are transmitted serially.

13. The survey system of claim 1 further comprising:

in N respective transmit beamformers, multiple beams are generated from each of the N message components and in a summation block the beams are combined to produce a summation block output.

14. The survey system of claim 1 further comprising:

respective hardware pipelines for receiving T hydrophone signals from an array of T hydrophones; and,

the T hardware pipelines providing T hardware pipeline outputs.

15. The survey system of claim 14 further comprising:

signals derived from each of the T hardware pipeline outputs providing N inputs to software pipelines such that (N×T) software pipeline inputs are provided; and,

software pipeline outputs corresponding to the (N×T) software pipeline inputs.

16. The survey system of claim 15 further comprising:

each of N receive beamformers receiving T software pipeline outputs such that no beamformer receives more than one signal derived from the same hydrophone; and,

respective processors receiving the outputs of the N beamformers to provide a survey result or an intermediate survey result.

17. The survey system of claim 16 wherein the hardware pipeline includes sequential signal processing through a first amplifier, a low-pass anti-aliasing filter, a second amplifier, and an analog to digital converter.

18. The survey system of claim 17 wherein the software pipeline includes sequential signal processing through a mixer, a bandpass filter, a decimator, and a matched filter.

19. The survey system of claim 18 wherein there are 64 or more hydrophones.

20. The survey system of claim 18 wherein there are 128 or more hydrophones.