Water, spray and humidity: what troubles a drone over water, in spray and in fog

Water causes three kinds of trouble: getting wet (rain, spray and condensation reach electronics and motors), being fooled (reflection and transmission at the surface make cameras and rangefinders misjudge height and speed), and being lost (anything that falls in is hard to recover or investigate). Near the sea, salt adds slow corrosion of metal parts and contacts.

The answers come in three parts: protect the aircraft from water, use positioning that the surface cannot fool, and hand underwater work to a different machine. Water resistance is expressed by the IP code (IEC 60529), and some aircraft are rated for flight in rain. But a rating has conditions; it does not promise survival in continuous spray or immersion.

Water is everywhere in inspection: beneath and around river bridges, on slopes, levees and rivers, on dam faces and outlet works, in damp sewers, at offshore wind turbines, along ports and quays and on ships and offshore structures. The closer to water, the faster things deteriorate and the harder they are to reach.

• Decide how to fly over water: for low passes near the surface, choose settings that do not rely on downward sensors (GNSS and barometric hold) or keep ample height manually.
• Read the conditions behind the IP rating: check the manufacturer’s rules for rain operations, not just the number. Flying into the spray of a discharging dam is another matter entirely.
• Plan for ditching: have a boat or float ready for recovery over water, and decide where you will write the aircraft off. A battery in water can itself be hazardous.
• Wash off salt and water: after flying near the sea, wipe the aircraft down and check connectors and moving parts. Never store it damp.
• Prevent condensation from temperature swings: moving from a cold vehicle to humid air, or from a cold waterside into a warm building, let the aircraft acclimatise inside its case before opening.
• Share the underwater part with ROVs or divers: for members crossing the waterline, align aerial and underwater viewpoints in the record.

In Japan, aviation law does not uniformly forbid flying over rivers or the sea. But waters have their own managers — river administrators, port authorities, the Japan Coast Guard — and depending on place and time, permits or notifications may be required. Navigation channels, fishing areas and announced dam discharges call for particular care.

Underwater drones fall outside aviation law, but shipping-safety rules apply in ports and channels. Related: wind & turbulence, GNSS-denied, cold & icing, world regulations.

• Inspection in steady rain or heavy spray: even if the aircraft can fly, lens droplets often ruin the images. It still comes down to waiting for dry weather.
• Turbid water: rivers and reservoirs are often murky, so underwater cameras must get very close. Sonar shows shape but struggles to measure crack widths.
• Members at the waterline: the splash zone, wetted and dried by waves, corrodes fastest yet is hard to image from either air or water.
• Offshore operations: launching and recovering from vessels, swell and salt. Offshore inspections have narrow weather windows and still depend heavily on human logistics.

Aerial and underwater drones head out together and record above and below the surface as one continuous 3D model. Rain-tolerant aircraft and water-shedding lenses cut the wait for dry weather, and ports and offshore sites have docks where aircraft return, dry off and recharge. Waterside assets are watched regularly without anyone launching a boat. That is the editors’ outlook.