System and method of range estimation

1. A method of estimating range to a surface of a body of water, the method comprising:

transmitting at least one acoustic signal through the body of water;

receiving a plurality of signals reflected from the surface;

generating at least one weighted sum based on data indicative of the reflected signals and an estimate of sidelobe coupling; and

estimating a distance to the surface based on the weighted sum.

2. The method of claim 1 , wherein the acoustic signal comprises a pulse.

3. The method of claim 1 , wherein transmitting the acoustic signal comprises transmitting the same signal in multiple directions.

4. The method of claim 1 , wherein transmitting the acoustic signal comprise transmitting the acoustic signal from a transducer oriented so as to reflect the signal from a bottom surface of the body of water.

5. The method of claim 1 , wherein receiving the reflected signals comprises receiving reflected signals from at least two different directions.

6. The method of claim 1 , wherein generating the at least one weighted sum comprises:

weighting a first reflected signal; and

subtracting the weighted first reflected signal from a second reflected signal.

7. The method of claim 1 , wherein the estimate of sidelobe coupling comprises an a priori estimate of sidelobe coupling.

8. The method of claim 1 , wherein estimating the distance comprises replacing values of data indicative of amplitude of the received signals that are below a threshold with a specified value.

9. The method of claim 8 , wherein the specified value is equal to the threshold.

10. The method of claim 1 , wherein estimating the distance comprises:

convolving data indicative of the received signals with a detection filter to produce a convolved signal;

locating the highest peak on the convolved signal; and

comparing the highest peak to a threshold.

11. The method of claim 1 , wherein transmitting the acoustic signal comprises transmitting four beams respectively from transducers in a Janus beam configuration, and wherein receiving the reflected signals comprises receiving four waveforms via the transducers.

12. A method of estimating range to a surface of a body of water, the method comprising:

transmitting at least one acoustic signal through the body of water;

receiving a plurality of signals reflected from the surface; and

estimating a distance to the surface based on data indicative of the received signals and an estimate of sidelobe coupling,

wherein transmitting the acoustic signal comprises transmitting four beams respectively from transducers in a Janus beam configuration, and wherein receiving the reflected signals comprises receiving four waveforms via the transducers,

wherein estimating the distance comprises generating four transformed waveforms, wherein for each received waveform weighted versions of the other three waveforms are subtracted from the received waveform.

13. A method of estimating range to a surface of a body of water, the method comprising:

transmitting at least one acoustic signal through the body of water;

receiving a plurality of signals reflected from the surface; and

estimating a distance to the surface based on data indicative of the received signals and an estimate of sidelobe coupling,

wherein transmitting the acoustic signal comprises transmitting four beams respectively from transducers in a Janus beam configuration, and wherein receiving the reflected signals comprises receiving four waveforms via the transducers,

wherein the estimate of sidelobe coupling comprises an estimate of sidelobe coupling between a selected one of the beams and at least one other beam, wherein the selected beam is oriented toward the surface.