Uncrewed Aircraft to Measure the Boundary Layer

The advent of small, uncrewed aircraft systems (sUAS) for atmospheric research offers opportunities to make unique meteorological measurements in the lowest layer of the Earth’s atmosphere. ARL’s ATD Division in Oak Ridge, TN uses sUAS to measure how temperature and relative humidity change with altitude, map the temperature and reflectivity characteristics of the Earth’s surface, and perform storm damage assessment in a never-before-available way that is faster, cheaper, and safer than using manned aircraft.

ARL’s Fleet of Aircraft

ARL’s ATD Division in Oak Ridge, TNARL currently has four sUAS that it flies on a regular basis, including three multi-rotor copters and one fixed-wing aircraft. The primary purpose of two of the multi-rotor aircraft (a DJI S-1000 and a Meteomatics Meteodrone SSE ) is to make measurements of temperature, relative humidity, and winds (Meteodrone only) as a function of altitude above the Earth’s surface. The third multi-rotor (a Microdrone MD4-1000 ) carries a LiDAR (Light Detection And Ranging) system to make high-resolution 3-D measurements of the Earth’s surface. The fixed-wing aircraft, a BlackSwift Technologies S2 has a payload module to make images of the Earth’s surface in multiple wavelengths to look at incoming and reflected solar radiation, as well as to measure in-situ air temperature and relative humidity. ARL is acquiring a second BST S2 with a different payload module to make in-situ measurements of 3-D atmospheric turbulence and flux measurements of CO2 and CH4.

Operations

All sUAS operated by ARL have approval from both the U.S. Federal Aviation Administration (FAA) and NOAA’s Aircraft Operations Center (NOAA/AOC) to fly under visual flight rules (VFR) weather conditions and within line of sight of the ground-based pilot.
ARL’s ATDD has several sites in the Knoxville area to test and operate each aircraft. ARL has agreements with Knox County Radio Control (KCRC) in Solway, TN, House Mountain Radio Control (HMRC) in Corryton, TN, and the Oliver Springs Airport in Oliver Springs, TN to fly sUAS aircraft up to 3000 feet above ground level. ARL also has a meteorological tower at the Oliver Springs Airport  to provide reference meteorological measurements that can compare to instruments on the sUAS to verify their performance; data from Oliver Springs is available on this page.

Field Studies

ARL used the DJI S-1000 (Octocopter) and the Microdrone MD4-1000 to support research to study the formation of severe thunderstorms and tornadoes over Northern Alabama in the spring of 2016 and spring of 2017. The Verifications of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE) experiment used a large suite of instruments to probe the Earth’s boundary layer both remotely and in-situ. Data from the S-1000  was combined with data from flux towers, microwave radiometers, Doppler radar and LiDAR systems, as well as radiosonde balloons and space-based remote sensing measurements to help form a more complete picture of how the boundary layer changes prior to the onset of severe thunderstorms and tornadoes. The S-1000 was also used to document areas of damage from a tornado that struck near Hartselle, Alabama on 31 March, 2016. NOAA Technical Memos from the 2016 and 2017 VORTEX-SE field campaigns are available here (2016) and here (2017) .

ARL participated in the Land-Atmosphere Feedback Experiment (LAFE) in the summer of 2017 at the Department of Energy’s Atmospheric Radiation Monitoring (DOE ARM) site near Lamont, Oklahoma. The DJI S-1000 and the Microdrone MD4-1000 both measured temperature and humidity in the lowest 300 meters of the atmosphere and were used to map the Earth’s skin temperature during three intensive observation periods (14 August, 15 August, and 17 August 2017). A NOAA Tech Memo from the 2017 LAFE field campaign is available here .

During the Great American Eclipse on 21 August 2017, ARL went to a site near Ten Mile, TN, located about 50 miles southwest of Knoxville, to take observations using the Octocopter. The purpose of this study was to better understand the response of the land surface and lower atmosphere to the effects of eclipse totality, which was 2 min 38 sec at this site. The team performed eight flights within a 2.5 hour window of totality and noted marked changes in near-surface temperature and moisture fields that were detectable until one hour after totality. Two minutes prior to totality, the sUAS ascended to 1200 feet AGL where it hovered during totality before descending. In the time lapse video in the sidebar, the left side view is from a GoPro camera installed on the underside of the sUAS. The right side shows the land surface temperature differences obtained from a downward-pointing infrared camera during this time. In this 47 second video, which covers an 8 minute time span, we observe the darkening and then re-lighting of the land surface, which corresponded with decreases in land surface temperature during this time. More details appear in a paper entitled Observations and numerical simulation of the effects of the 21 August 2017 North American total solar eclipse on surface conditions and atmospheric boundary-layer evolution.

In order to test evaluate emerging technologies that will ultimately allow for sUASs to be operated beyond visual line-of-sight, the BST S2 and the Meteomatics Meteodrone SSE were tested during an experiment at the Avon Park Air Force Range in Avon Park, Florida in March, 2019. The purpose of this experiment was to evaluate technologies such as solid-state radar systems and real-time air traffic display systems while simultaneously flying several sUAS to altitudes of 1 km and above. These systems will ultimately allow sUASs to be operated safely in the National Airspace System beyond visual line-of-sight, which is critical to fulfill weather forecasting needs of the future. More details about the Avon Park experiment are available on the ARL News page and also in a NOAA Technical Memorandum

In summer and fall of 2019, ARL participated  in the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 (CHEESEHEAD 2019) study near Park Falls, WI with collaborators from the University of Wisconsin and other NOAA laboratories. The purpose of CHEESEHEAD is improved understanding of how plants affect the weather on a local scale. Acquiring this understanding requires making many measurements of temperature, moisture, and wind within and above the forest canopy which ARL’s sUAS will be critical component.  ARL operated its Meteomatics SSE to sample low-level temperature, moisture, and wind fields, as well as its MD4-1000 sUAS outfitted with a downward-pointing lidar to capture fine-scale changes in surface roughness for three campaigns. Following CHEESEHEAD, ARL performed sUAS flights with its Meteomatics SSE and BST S2 during the Albuquerque International Balloon Fiesta to assist with weather forecasting operations during the event.

ARL continues to expand its arsenal of sUAS platforms and instrumentation and explore options to fly to higher altitudes than ever before. ARL is now operating its sUAS up to 1 km altitude at the Oliver Springs Airport, located approximately five miles north of the lab, and to provide this information in near real-time to the local National Weather Service Weather Forecast Office in Morristown to assist with their weather forecast operations.