Observations of Wind in Early Morning Transitions in Complex Terrain

Observations of the early morning transition of the lower atmospheric boundary is presented. The objective of the study is to monitor lower atmospheric boundary layer (ABL) wind evolution during the daily diurnal cycle using small unmanned aerial systems. Various studies have demonstrated using a fixed wing or a multirotor unmanned aerial vehicle (UAV) equipped with sensor packages and flown with proper flight patterns to capture the evolution of these atmospheric properties. An approach is presented using a single multirotor integrated with a 3D ultrasonic anemometer. Vertical profiles and horizontal transects are taken. A total of three cases are examined and alongside a validation study of the sensors. The first test case consists of heterogonous environment at the Marena Mesonet in Stillwater, OK. The terrain is consisting of grassy fields populated with trees throughout and elevation is relatively constant. This site additionally provides a location for validation for sensor packages to be compared to the weather towers maintained by the Oklahoma Mesonet Network. Validation test are conducted at Kessler Atmospheric and Ecological Field Station in Purcell, OK. The Kessler site allows for repeatable sensor validation similar to the Marena and provides methods to validate airborne wind vector measurements at higher altitudes using LIDAR. The second test case is the urban and complex environment proposed for the study is on campus of Oklahoma State University an area congested with buildings and manmade structures compared to an off campus site such as the public Arlington Park where it is not crowded by buildings. The third test case consists of the Gloss Mountains. This area provides another study of influences due to complex terrain of naturally occurring large land formations. Preliminary tests show sensors are capable of measuring and determining wind vectors with an airborne sensor.

The diurnal cycle plays a vital impact in the formation of weather events, mixture of chemical composition between the atmospheric boundary layer and the troposphere, and used in climate prediction models to improve weather forecasts. During the course of the day under clear skies the ABL will undergo heating from the sun at sunrise to a convective boundary layer while during sunset, heat loss causes the space to a thin nocturnal boundary layer. The structure of these lower atmospheric events largely depend on seasons, surrounding geography, and terrain. In open fields under clear skies there is an expected increase in temperature and decrease in humidity. However, in urban environments due to decrease surface area of vegetation and exposed ground replaced with roadways and drainage systems, water is forcibly removed disrupting the normal diurnal cycle. The reduction in available moisture increases the rate at which temperature changes in that area.