A system for use in conjunction with an underwater dredging apparatus having a power shovel with a bucket connected to a power housing by two articulated manipulator arms. The articulation of the manipulator arms relative to each other as well as one manipulator arm relative to the power housing controls both the horizontal position of the bucket as well as the vertical depth of the bucket. The system includes a data processor, a depth sensor which is attached to one manipulator arm at a predetermined position, as well as angle sensors which provide output signals of the relative angle of the manipulator arms relative to each other as well as relative to the power housing. The data processor is programmed to calculate the vertical depth of the bucket as a function of the depth sensor as well as the angle sensors. Once the bucket depth is calculated, the processor displays the bucket depth on a video display.
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