Method for all ocean-terrain ships covert velocity reference

1. A SONAR processing method comprising:

transmitting pulses toward an ocean bottom from a moving underwater object;

receiving pulse echoes, wherein the pulse echoes collectively define a bottom return;

filtering data from the bottom return to generate a filtered echo envelope;

obtaining a first derivative of the filtered echo envelope at each of a plurality of locations;

identifying a location of a first pulse echo and subsequent pulse echoes in the bottom return based on analysis of the first derivatives; and

estimating velocity of the moving underwater object based on the pulse echoes.

2. A SONAR processing method comprising:

transmitting pulses toward an ocean bottom from a moving underwater object;

receiving pulse echoes, wherein the pulse echoes collectively define a bottom return;

identifying a location of the first pulse echo and subsequent pulse echoes;

calculating MT, which is the true modeling of distance traveled by the underwater object between transmission of the pulses;

calculating modeling error by subtracting the distance traveled between correlated pulses from MT; and

providing a continuous estimate of velocity by correcting velocity estimates obtained from an inertial device by the modeling error.

3. A SONAR processing method comprising:

transmitting pulses toward an ocean bottom from a moving underwater object;

receiving pulse echoes, wherein the pulse echoes collectively define a bottom return;

detecting highly-sloped ocean-bottom terrain; and

changing a parameter related to the transmitting of pulses.

4. The SONAR processing method of claim 3 wherein the parameter is the time between pulses.

5. The SONAR processing method of claim 3 wherein the parameter is the carrier frequency of transmit pulses, and wherein some transmitted pulses have different carrier frequencies than other transmitted pulses.

6. The SONAR processing method of claim 3 wherein the parameter is the phase of transmit pulses, and wherein some transmitted pulses have different phase than other transmitted pulses.

7. A SONAR processing method comprising:

(a) transmitting pulses toward an ocean bottom from a moving underwater object;

(b) receiving pulse echoes, wherein the pulse echoes collectively define a bottom return;

(c) filtering data from the bottom return to generate a filtered echo envelope;

(d) measuring signal plus noise from the filtered echo envelope;

(e) estimating noise;

(f) calculating a required signal-to-noise ratio using a SONAR range equation;

(g) calculating a measured signal-to-noise ratio using results from operations (d) and (e); and

(h) increasing at least one of a transmit power level or a pulse width when the measured signal-to-noise ratio is less than the required signal-to-noise ratio.

8. A SONAR processing method comprising:

transmitting pulses toward an ocean bottom from a moving underwater object;

receiving pulse echoes, wherein the pulse echoes collectively define a bottom return;

filtering data from the bottom return to generate a filtered echo envelope;

obtaining a first derivative of the filtered echo envelope at each of a plurality of locations;

restricting selection of pulse echoes for velocity calculation from a first region of the bottom return that corresponds to a region of the filtered echo envelope that has near-zero first derivatives; and

estimating the velocity of the underwater object using pulse echoes from the first region of the bottom return.

9. A SONAR processing method comprising:

transmitting pulses toward an ocean bottom from a moving underwater object;

receiving pulse echoes, wherein the pulse echoes collectively define a bottom return;

storing a pulse location data sample number for which a first sufficient bi-pulse correlation occurs;

measuring and storing the mean amplitude of the following X data samples, where X is proportional to a depth of the ocean bottom and composite transmit and receiver beam pattern;

advance Y data samples, wherein Y is about X/10;

continue bi-pulse amplitude correlation until one of the following conditions occur:

(a) a second sufficient bi-pulse amplitude correlation occurs, wherein if condition (a) occurs, then a mean amplitude of the following X data samples are measured; or

(b) a predefined search window ends;

continue processing until the end of pulse location search window;

designating, as initial pulse location, the data sample number for which sufficient bi-pulse amplitude correlation and maximum amplitude is measured in the following X data samples;

form pulse-pairs based on the initial pulse location; and

estimate velocity of the underwater object.

10. A SONAR processing method comprising:

transmitting pulses toward an ocean bottom from a moving underwater object;

receiving pulse echoes, wherein the pulse echoes collectively define a bottom return;

determining if the bottom return is an extreme specular return; and

increasing at least one of the transmit power level or pulse width by measuring signal plus noise power for a number of pulse echoes for a region greater than a 3 dB transmit beam point width value when the bottom return is an extreme specular return.