Dust and smoke: what a drone relies on when the air itself is opaque

Fine airborne particles scatter light. Images turn milky, and the more light you add, the more the near particles glow and hide what lies beyond. LiDAR pulses bounce off particles and return points that look like a wall in mid-air. Dust also settles on the aircraft, clogging motors, sensor windows and cooling paths.

The answers are to choose sensors that resist scattering, build aircraft that neither stir up nor ingest dust, and choose when to fly. Longer-wavelength thermal cameras and millimetre-wave radar are less affected by fine particles than visible light. LiDAR processing that keeps only the last return can strip out many particle points.

Dust and smoke are densest in enclosed spaces: ash in boilers and furnaces, soot in chimneys, rock and coal dust in mines, and poorly ventilated or under-construction tunnels. All overlap with darkness and GNSS denial, leaving sensors few alternatives.

• Let the dust settle first: enter after ventilation following shutdown, or after wetting and cleaning. Ask the site to schedule drone inspection into its work plan.
• Decide the sensor mix: do you need visual images, or will a temperature map do? In dense dust, survey first with thermal and LiDAR, then take close-ups only where visibility allows.
• Choose adjustable lighting: can brightness and direction be changed, and are the lights mounted away from the camera?
• Make post-flight maintenance routine: clean motors, bearings and sensor windows every time, and log hours in dusty sites to schedule part replacement.
• Plan link and retreat: decide whether to hold or retrace the recorded path when visibility goes. Relying on manual piloting through dense smoke is a dangerous plan.
• Protect the crew too: whoever retrieves the aircraft gets covered in dust. Put respirators and other personal protection into the procedure.

Flights inside boilers or mine drifts are often treated as indoor in Japan and fall outside the aviation flight rules. But dusty sites have occupational safety rules: dust-work controls, respiratory protection, and checks for oxygen deficiency and gas in enclosed spaces. Coal, metal and grain dust can explode in their own right, and a drone carrying a battery and motors can be an ignition source.

Related: explosive atmospheres, oxygen deficiency & toxic gas, confined spaces, darkness, world regulations.

• Visual inspection through dense dust: no sensor can resolve cracks or wall thinning through thick dust. Waiting for it to settle remains the best answer.
• Radar-based autonomy: research on flying through dust with millimetre-wave radar is advancing, but mapping accurate enough for inspection in tight spaces is still mostly at the research stage.
• Small, dust-proof aircraft: seal them and heat builds up; open them and particles get in. Balancing cooling and dust protection is hardest on small airframes.
• Flying in combustible dust: drones certified for use in potentially explosive dust remain scarce.

Drones entering boilers and mines fuse radar, LiDAR and thermal imaging, keeping track of their position and the walls even in dust. They choose flight paths that stir up little and seize the moment visibility clears to take close-ups. Far fewer people climb dusty scaffolds. That is the editors’ outlook.