The maximum operating altitude is up to 140 m, depending on seabed composition, acoustic noise and sedimentation in the water column.
The minimum operating altitude is 0.5 m. Below this altitude the velocity errors begin to grow very large but velocity estimates can still be made to around 0.3 m.
Mounting the DVL as high as possible on the vehicle while maintaining line of the sight for all 4 beams allows for the best results in very low altitude scenarios.