A self‐calibrating diver’s rangefinder

An underwater rangefinder with a self‐calibrating facility has been developed for use by divers as an accurate surveying instrument. It can measure range to a passive target or transponder to ±0.1 m and local acoustic velocity to ±0.2 ms−1 with a built‐in velocimeter which updates the displayed range automatically. Its design, operation, and applications are presented.