Surface Roughness and Wind Profiles
How different terrain types modify wind speed and create turbulence
Power Law Wind Profile:
Wind speed increases with height above surface, but the rate depends on terrain roughness. Rougher surfaces create more friction and steeper wind gradients.
V(h) = V(h₀) × (h/h₀)^αWhere α = terrain coefficient (higher values = rougher terrain)
Open Water
Coefficient: 0.10
- • Minimal surface friction
- • Lowest wind gradient
- • Consistent wind patterns
- • Least turbulence
Open Flat
Coefficient: 0.15
- • Grasslands, airports
- • Low surface roughness
- • Smooth wind transitions
- • Minimal obstacles
Agricultural
Coefficient: 0.20
- • Crops, scattered trees
- • Moderate surface friction
- • Some turbulence near obstacles
- • Seasonal variations
Suburban
Coefficient: 0.30
- • Houses, trees, neighborhoods
- • Significant wind shear
- • Complex turbulence patterns
- • Variable wind directions
Urban
Coefficient: 0.40
- • Dense buildings, skyscrapers
- • Highest surface friction
- • Extreme turbulence
- • Urban canyon effects
Ground Effect Phenomena
How proximity to the ground affects drone aerodynamics and performance
Beneficial Effects
- • Increased lift efficiency near ground
- • Reduced induced drag
- • Improved hovering performance
- • Lower power requirements
- • More stable hover in some conditions
Negative Effects
- • Reduced control authority
- • Turbulence from rotor wash
- • Dust and debris pickup
- • Asymmetric lift over uneven terrain
- • Potential loss of altitude control
Ground Effect Height Range:
Ground effect is most pronounced when flying at heights less than one rotor diameter above the surface. For most consumer drones, this is typically within 1-3 feet of the ground.
Caution: Ground effect can make takeoffs feel easier but may cause sudden altitude loss when climbing out of ground effect. Always maintain adequate power reserves.
Terrain-Specific Flight Challenges
Mountain/Hill Flying
Challenges:
- • Orographic lift and downdrafts
- • Wind acceleration over ridges
- • Rotor turbulence on lee sides
- • Rapid weather changes
Safety Tips:
- • Approach from windward side
- • Maintain extra altitude buffer
- • Monitor for sudden wind changes
- • Avoid lee side operations
Urban Environment
Challenges:
- • Building wake turbulence
- • Urban heat island effects
- • Wind channeling between buildings
- • RF interference
Safety Tips:
- • Fly well above building heights
- • Avoid narrow urban canyons
- • Check for thermal currents
- • Monitor signal strength
Forest/Wooded Areas
Challenges:
- • Mechanical turbulence from trees
- • Variable canopy heights
- • GPS signal blockage
- • Emergency landing difficulties
Safety Tips:
- • Maintain high altitude clearance
- • Use ATTI mode if GPS poor
- • Plan safe landing zones
- • Monitor battery more closely
Coastal/Water Areas
Challenges:
- • Sea breeze/land breeze effects
- • Salt spray and corrosion
- • Reflective surface GPS issues
- • Limited emergency landing options
Safety Tips:
- • Account for thermal effects
- • Protect from salt exposure
- • Maintain safe distance from water
- • Check tide and weather patterns
Terrain-Induced Turbulence
Mechanical Turbulence
Created when wind flows around obstacles
- • Buildings, trees, hills
- • Creates eddies and vortices
- • Most intense on downwind side
- • Height depends on obstacle size
Thermal Turbulence
Rising air from heated surfaces
- • Parking lots, buildings, pavement
- • More pronounced on sunny days
- • Creates convective currents
- • Can cause altitude fluctuations
Orographic Turbulence
Mountain wave and rotor effects
- • Wind flow over mountains
- • Can extend many miles downstream
- • Severe downdrafts possible
- • Affects large geographic areas
High-Risk Turbulence Zones
- • 15-20x obstacle height downwind of large structures
- • Ridge lines and mountain passes
- • Interface between different terrain types
- • Areas with significant temperature gradients
- • Narrow valleys with channeled wind flow
Terrain-Aware Flight Safety
Pre-Flight Terrain Assessment
- ✓ Study topographic maps of the area
- ✓ Identify potential turbulence sources
- ✓ Note wind direction relative to obstacles
- ✓ Plan safe corridors and escape routes
- ✓ Check for thermal sources (buildings, pavement)
- ✓ Consider seasonal vegetation changes
During Flight Operations
- ✓ Maintain extra altitude over rough terrain
- ✓ Approach obstacles from upwind side
- ✓ Monitor for sudden altitude or attitude changes
- ✓ Avoid flying in lee of large obstacles
- ✓ Be prepared for increased battery consumption
- ✓ Keep escape routes clear
Terrain Rule of Thumb: When flying near obstacles, maintain at least 500 feet of clearance or 2x the obstacle height, whichever is greater. For mountains and ridges, this clearance should be significantly higher.