Methods and systems for determining a depth of an object

A method comprising:

• providing an autonomous vehicle (AV) with a first estimated position of a target;
• directing the AV to travel toward the first estimated position at a constant velocity;
• receiving, from a 2-dimensional sensor of the AV, echo signals of transmitted sonar signals, the echo signals indicating a range and an azimuth of the target;
• measuring range of the target over time using from the echo signals;
• for each of a plurality of candidate depth differences, generating data corresponding to a change in range of the target over time that would be expected if the AV and the target had the candidate depth difference;
• determining a depth difference of the AV and the target as the one of the plurality of candidate depth differences for which the generated data has a best fit to the measured change in range of the target over time;
• and
• in response to a depth difference existing:
• determining a direction of the depth difference, the direction indicating whether the target is above or below the AV, and
• re-directing the AV toward a second estimated position of the target generated from the depth difference and the direction of the depth difference.