I have an M300 and wanted to do close-approach inspections of bridges and concrete structures over water. How reliable is the Visual Positioning mode over water and are there any preventive measures that I can take to ensure the safety of the drone?

I've used the M210 several times under bridges and it's essentially a free fly situation. The M210 vision system did not respond well to the water texture causing platform drift in the GPS denied environment. In some situations even the altitude hold was inconsistent.

We do currently operate an M300 but I'm yet to attend these environments again. I'm sure the proximity sensors will ensure no adverse interactions with the surrounding structures.

I would almost suggest a 2 person operation with a dedicated camera operator for data collection and a pilot focussed upon the device.

We use the CSM radar, don't trust the other sensors ( = manual flight and know your own skills ). Be very careful with the RTH settings ( if contact lost...)

Ideally ATTI mode especially with the rebar and other from bridge/concrete structures.