I have used An Octans Gyro with both 1200kHz and 300kHz RDI Workhorse Navigator DVL dopplers.
The 300kHz doppler will hold bottom lock up to 150m off the bottom.
The 1200kHz doppler will only hold lock to 25m, but it will hold lock closer to the seabed than the 300kHz unit.
There is also a 600kHz version, but I have not used it
The random doppler drift is a couple of mm/s when the vehicle is stationary, there is a drift component related to vehicle velocity so as the vehicle speed increases the drift increases. The doppler accuracy is greatly improved by inputting the current local bottom sound velocity and calibrating the Doppler to the Gyro
RDI has a new Doppler called the PAVs which claims to work to 500m altitude, but I have not tried it yet.
When flying the ROV under closed loop control the vehicle station keeping accuracy will depend on the thruster control loop. In my experience I have seen much better station keeping on ROVs with electric thrusters than those with hydraulic ones. I have made autopilot moves in the order of 100mm steps.
It is difficult to say what the relative accuracy is up off the seabed since you have no visual reference. Against the USBL nav the accuracy looks similar to closer to the seabed.
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