Hello @kamilshamsi2695,
Optical flow cameras on multicopters work by looking at the ground and analyzing how it moves, this enables a better position hold, but it doesn’t replace the GPS enough to support missions.
It also requires a sonar to tell the distance from the ground (to correct for the angular variations of the aircraft)
Since visibility in water is not great, there isn’t much gain from using such a setup with optical flow, you would only be able to use it with a good sight of the seabed and would also require sonar data for seabed distance information.