UAV Operations: Lessons Learned and Best Practices

This list was created for drone and user safety and does not define best data collection practices

Contact: Jennyrogers@talltimbers.org

Obstacle Avoidance

Different drones use different obstacle avoidance systems, and operators should understand their limitations before every flight.

DJI Mini 5

  • Uses LiDAR-based obstacle detection.
  • Does not reliably detect small branches.
  • Does not provide obstacle detection when flying in reverse.
  • Exercise caution when operating near forest canopies or when backing up.

DJI Matrice 300 RTK and Matrice 4TD

  • Use six-direction visual sensors and Time-of-Flight infrared sensors rather than LiDAR.
  • Visual sensing performance is significantly degraded in low-light conditions.
  • The Matrice 4TD touts improved performance but should not be blindly trusted.

Common Issues

  • The Matrice obstacle avoidance system may detect objects up to 50 ft below the aircraft. Unexpected obstacle warnings may be caused by terrain or vegetation beneath the drone.
  • Digital light sensor wires can occasionally move into the sensor field of view and trigger false obstacle warnings. If this occurs, secure the wiring and continue monitoring.

Hazards to Watch For

  • Power lines
  • Communication towers
  • Birds
  • Crop-dusting aircraft
  • Tree canopies and isolated tall trees

Best Practices

  • Verify that obstacle avoidance is enabled before takeoff.
  • Confirm obstacle warning distances are appropriately configured.
  • Do not assume obstacle avoidance is functioning correctly simply because the landing spotlight activates.

Lesson Learned: A previous aircraft loss occurred after operators assumed obstacle avoidance was active based solely on the landing spotlight indication.

Weather Resistance

Understand the environmental limitations of each aircraft before operating near precipitation.

IP Ratings

  • Matrice 300 RTK: IP45
    • Not dust-tight.
    • Protected against low-pressure water jets.
  • Matrice 4TD: IP55
    • Protected against limited dust ingress.
    • Resistant to low-pressure water jets.

Neither aircraft is waterproof and should not be flown in rain beyond manufacturer recommendations. Learn more about IP ratings 

Smoke Operations

Smoke can interfere with normal drone operation.

Potential issues include:

  • Obscured visual sensors.
  • False obstacle detections.
  • Reduced situational awareness.

Use extra caution when operating within or near dense smoke plumes.

Flight Altitude and Terrain Following

Ground Reference Considerations

Mission altitude is referenced to the terrain elevation at the launch location unless terrain-following functionality is explicitly enabled. This means along its route the drone height in reference to the tree tops may be variable.

Tradeoffs of Higher Flight Altitudes

Benefits:

  • Improved visibility.
  • Better image overlap and orthomosaic generation.
  • Increased obstacle clearance.

Drawbacks:

  • Reduced spatial resolution (larger pixel size).
  • Reduced LiDAR point density and intensity.

Terrain Follow – Digital Elevation Model (DEM)

A Digital Surface Model (DSM) can be used with terrain-following missions to compensate for elevation changes.

However:

  • The built in “Download from the Internet”, ASTER GDEM, option is coarse resolution (30-m) from 2019 (or older) and contains vertical inaccuracies (~9 m) and other artifacts. 
  • Aircraft requires time to climb between elevation changes and terrain-following systems may not react quickly enough to steep terrain or tall vegetation.

Terrain Follow – Real Time Follow

Tall Timbers has not evaluated real-time terrain-following functionality. Exercise extreme caution, particularly over water, where optical sensors may become unreliable and LiDAR signals can be absorbed.

Minimum Recommended Clearance

Maintain at least 50 ft of clearance above the tallest vegetation in the area.

Lesson Learned: Tall Timbers lost an aircraft after it struck the top of a tree while flying at 120 ft AGL using a DEM-based terrain-following workflow in low lighting. 

The tallest tree recorded at Tall Timbers is approximately 40 m (131 ft) (source: Erin Wachter).

 

 

Batteries

Charging and Swapping

  • Verify all batteries are fully charged the evening before a mission.
  • Smart batteries are set to automatically discharge during storage.
  • It is best practice to land the drone at 30% charge. 
  • Battery discharge is not linear but S-curved so a lower charge drains more quickly. 
  • Temperature is a confounding variable in battery capacity.

Auto-discharge settings:

  • Matrice 4TD: 7 days
  • Matrice 300 RTK: 2 days

Storage and Maintenance

  • Cycle batteries at least once every three months if not regularly used.
  • Store batteries out of direct sunlight, excessive heat can cause batteries to be temporarily disabled.
  • Avoid storing batteries attached to charger but not connected to a power source as this can cause additional discharging.

If a battery overheats:

  1. Move it to a cool, air-conditioned environment.
  2. Allow it to cool gradually.
  3. Avoid placing ice packs directly against batteries, as condensation can introduce moisture into battery components.

Additional Best Practices

Launch and Landing

  • Use the orange launch pad whenever practical.
  • Confirm the gimbal has returned to a neutral position before landing the aircraft.

Sensor Protection

  • Avoid pointing the thermal camera directly at the sun for extended periods.

Firmware

  • Check for required firmware updates before leaving for the field.

Generator Issues

If the generator starts and immediately stalls:

  • Verify choke settings.
  • Excessive choking may flood the engine.
  • Carburetor cleaning may be required if the issue persists.

RTK Troubleshooting

Common RTK issues include connection failures and movement warnings.

If RTK fails to connect:

  1. Restart the RTK base station.
  2. Restart the aircraft 
  3. Attempt multiple times until a connection is established. 
  4. Consider moving into a more open location.

If the system reports that the RTK has moved:

  1. Land the aircraft safely.
  2. Power-cycle the RTK and aircraft.
  3. Confirm the RTK base is stable and protected from wind-induced movement.
  4. Re-establish RTK corrections before continuing.

Lesson Learned: If an RTK interruption occurs during a LiDAR mission, restarting the mission from the beginning may be preferable. RTK interruptions have previously produced elevation offsets of up to 30 ft between flight lines, requiring significant post-processing corrections.