Wind Analysis for Drone Flight | Power Law Wind Profiles & Terrain Effects

Power Law Wind Profile

The mathematical model used to predict wind speed changes with altitude

The power law wind profile, established through extensive meteorological research, provides the mathematical framework for predicting wind speed variations with altitude in the atmospheric boundary layer. (NREL Wind Resource Assessment Handbook, 2010)

Formula:

V(h) = V(h₀) × (h/h₀)^α

Where:

V(h) = Wind speed at height h
V(h₀) = Wind speed at reference height h₀
α = Power law exponent (terrain coefficient)

Terrain Coefficients (α)

Open Water: 0.10
Open Flat Terrain: 0.15
Agricultural Land: 0.20
Suburban: 0.30
Urban: 0.40

Source: DOE Wind Energy Resource Atlas

Practical Impact

Higher coefficients indicate greater wind speed increase with altitude
Rough terrain surfaces generate increased atmospheric turbulence
Buildings and obstacles create localized wind shadows and channeling effects
Valley topography can funnel and amplify wind speeds significantly

Wind Speed Categories

Wind speed categories for drone operations based on aviation meteorology standards and field testing data

Wind speed categories are established through extensive flight testing and aviation safety research. (FAA Part 107 Operations Guidelines)

0-8 mph (0-13 km/h)

Optimal Conditions: Minimal impact on flight performance. Stable hover capability and precise maneuvering operations possible.

8-15 mph (13-24 km/h)

Good Conditions: Slight increase in battery consumption. Smaller and lightweight drones may experience reduced performance.

15-25 mph (24-40 km/h)

Moderate Winds: Significant impact on flight stability. Requires experienced pilot skills and increased attention.

25-35 mph (40-56 km/h)

Challenging Conditions: Advanced piloting skills required. Flight operations should be reconsidered based on mission criticality.

35+ mph (56+ km/h)

Dangerous Conditions: Flight operations not recommended. Elevated risk of aircraft loss of control and potential damage.

Wind Speed vs Altitude

Wind speeds increase with altitude due to decreased surface friction effects. The rate of this increase depends on local terrain characteristics and atmospheric stability conditions. (Journal of Applied Meteorology, 2008)

Example Calculation:

Ground wind: 10 mph

Target altitude: 400 feet

Terrain type: Suburban (α = 0.30)

Reference height: 33 feet

Wind at 400ft = 10 × (400/33)^0.30 = 15.2 mph

This represents a 52% increase in wind speed from ground level to flight altitude.

Flight Safety Notice: Wind conditions must be assessed at the planned flight altitude, not surface level measurements alone. Wind speeds can increase substantially with altitude, particularly over open terrain where surface friction is reduced.

Turbulence and Wind Gusts

Sources of Turbulence

• Buildings and structures
• Trees and vegetation
• Terrain features (hills, valleys)
• Temperature inversions
• Mechanical turbulence from obstacles

Gust Factors

• Gusts can be 1.5-2x steady wind speed
• More common in unstable atmospheric conditions
• Particularly dangerous during takeoff/landing
• Can cause sudden altitude changes

Wind Shear Warning: Sudden changes in wind direction or speed can cause loss of control. Be especially cautious around buildings, cliffs, and temperature boundaries.

Wind Safety Guidelines

Best Practices

✓ Check wind forecast before flight
✓ Monitor real-time wind conditions
✓ Plan for increased battery consumption
✓ Maintain visual line of sight
✓ Have a safe landing area identified
✓ Start with low altitude test flight

Avoid Flying When

✗ Wind speed exceeds drone specifications
✗ Gusty conditions with rapid changes
✗ Approaching weather fronts
✗ Near large obstacles causing turbulence
✗ Temperature inversions present
✗ Visibility is reduced by dust/debris