Microscale Forecasting for Unmanned Aerial Systems

Unmanned Aerial Vehicles (UAVs) have the potential to make companies more efficient and save money. Certain precautions must be considered before taking flight with a UAV. Besides knowing the local aviation laws, flight rules, and safety measures, weather data must also be provided. Micro-scale forecasting below 1000ft AGL poses a challenge since most of our data is calculated for above 1000ft. In our study we collected data from a UAV with a weather package attached. We recorded the type of terrain of the launch area, such as open field, heavily treed, or urban area. The weather package gives temperature and humidity data and includes GPS data to measure any possible wind gusts. Wind can influence a small UAV (under 55lbs) in several ways. Takeoff requires calm winds below 20 KTS and fair weather. Fair weather for small UAV flight operations consists of calm to light winds, no precipitation, good visibility, and ceilings above 1000FT. The Visual Flight Rules are met with these standards. Most forecasts are for a general area and consist of different surfaces. For example, a forecast for Bexar County has extremely different surfaces; from skyscrapers to farmland. In the city, winds could be lighter due to buildings and friction, than they would be out near a field, thus a micro-scale forecast must be prepared for the flight. When making the forecast you need to consider the Planetary Boundary Layer, buildings, and surrounding topography. Open fields can produce higher winds since there is no friction to slow them down; and buildings can produce a tunneling effect creating strong winds. Low-level turbulence (LLT) occurs in the boundary layer caused by friction. LLT is strongest in unstable conditions, particularly in the afternoon when daytime heating is at its peak. Low-level wind shear is a change in wind speed and/or direction over a short distance. Two sources of wind shear that are most concerning for UAV operations are temperature inversions and surface obstructions. Vertical wind shear has the most adverse effect on aircraft of any type and can drastically alter lift.

Humidity and temperature can change the altitude density, affecting the UAV performance and battery life. As global warming is changing our average high temperature, our UAVs are feeling the effect also. In high temperature environments, the risk of overheating a battery increases stress on the UAV, causing poor performance. With a battery not working at its full potential, the risk of flyaway and lost-link could be a greater issue for the Remote Pilot in Command. For example, if a car has an inside temp of 70 degrees, within 30 minutes it could reach 100 degrees or more for an average South Texas day here in Bexar County. Our average flight temperatures are 90 degrees or higher. If our beginning flight temperature is at 90 degrees, within minutes the battery will feel the effect of 100+ temp, which could reduce the life or efficiency of the battery. Additionally, internal wires, plastics, and/or hardware are then susceptible to collateral damage. Overall the UAV, should be able to withstand high temperatures. Knowing the specifications of your UAV and battery will give a better performance out of your flight. More downtime between flights and shorter flight times will help the UAV return to its most optimal or stable temperature and extend the life of the battery and UAV.

Wind shear and turbulence can bring any aircraft down, so it is crucial to have a micro-scale forecast before flight operations begin. Damage to aircraft or personnel can occur without a proper forecast and knowledge of FAA regulations. The area and climatological data must be analyzed for a better understanding to make an accurate forecast. There is a plethora of information at our fingertips for gathering weather data such as websites and weather apps. Without doing the proper forecasting, a UAV flight can be limited by performance or even spell disaster by causing an unnecessary loss.