OU Researchers Share Findings from Finnish Expedition
Figure 1: Santiago Mazuera preparing a Coptersonde 2 UAS for flight under the Northern Lights in Hailuoto, Finland. Photo Credit – Brian Greene
OU Researchers Share Findings from Finnish Expedition
In February 2018, a team of researchers from five universities descended on a remote island on the Finnish side of the Bay of Bothnia to study the stable Arctic atmospheric boundary layer. The University of Oklahoma Center for Autonomous Sensing and Sampling (CASS) was invited to join the Finnish Meteorological Institute (FMI), The Geophysical Institute of the University of Bergen (UiB), University of Tubingen, and the University of Applied Science Ostwestfalen-Lippe (OWL) for ISOBAR, or Innovative Strategies for Observations in the Arctic Atmospheric Boundary Layer. The four-week sampling combined more conventional ground-based instrumentation such as sodars, lidar, flux stations, and sonic anemometers with small unmanned aircraft systems (UAS) to characterize various boundary layer parameters. Some of the unmanned aerial vehicles (UAVs) used were designed and built by the CASS team specifically to sample the lower atmosphere. Tony Segales, PhD student in Electrical and Computer Engineering and member of the CASS team, helped to develop the UAVs. He said, “The performance of our in-house UAVs in Finland was off the charts, especially considering the harsh conditions, encouraging us to keep developing cutting-edge designs for meteorological applications.”
Favorable weather conditions permitted the team to make nearly 100 successful flights to collect vertical profiles of carbon dioxide and thermokinematic parameters, estimate the temperature structure-function parameter, and gather photogrammetric and videographic surveys of the campaign area. In addition, the team achieved many firsts in operations, such as flying at night and beyond visual line of sight, and set new altitude records by climbing to 1800 m or 5900’ AGL. Additionally, the teams participated in intensive operational periods in conjunction with the other teams to collect continuous boundary layer profiles over the course of 16-24 hours. This provided a means to observe the diurnal evolution of the arctic boundary layer that would have been impossible by one crew alone.
Figure 2: Aerial photograph of the campaign team, including teams from OU, Tubingen, OWL, and UiB.
Figure 3: Skew-T Log-P diagram of temperature (red line) and dewpoint temperature (green line) measured from the OU CopterSonde from around midnight local time on the night of February 18, 2018. Winds are still being processed, so the hodograph appears empty. A very strong surface inversion was observed this evening, with temperatures increasing over 10 degrees Celsius in just 200 meters.
While the data is still being digested, preliminary results have been promising. Flying above the sea ice at night is a unique environment. With no sunshine to heat the surface, the ice cools down very quickly – much faster than the air right above it can. This results in temperatures that increase rapidly with height. This happens most nights around the world when it isn’t cloudy and there are calm winds, but sea ice is special because it cools off even faster than the land does. In fact, the CASS team observed an increase of 10 degrees Celsius (about 18 degrees Fahrenheit) between the ground and 200 meters (about 650 feet) on a few occasions (Figure 3). These kinds of temperature changes are usually only seen over hundreds of miles in the horizontal, which is why having the UAV technology to measure the vertical is so important.
Figure 4: Compilation of all vertical profile flights on February 10, 2018. The x-axis represents the time, and the y-axis is altitude above the sea ice, with temperature shaded. The vertical dashed lines represent the times of each flight for perspective.
While one vertical profile flight only provides a snapshot of the atmosphere at a particular instance in time, flying multiple times over the course of the day is useful to document how the atmosphere evolves with time. By looking at a composite view of these flights, numerous interesting features can be examined (Figure 4). In this case, we can see that the UAV flew higher with each flight – this is because the team was pushing the limits of how high the multicopter could reach, and ultimately set a CASS record of 1800 meters. This perspective of data also shows how temperature decreases faster closer to the surface, with a pocket of very cold air above this surface inversion. This is also just the perspective of flights from the OU platforms, which will eventually be combined with data from the other teams who took turns flying for a complete picture of the diurnal cycle of the Arctic boundary layer. According to Santiago Mazuera, an undergraduate in Aerospace Engineering and member of the CASS team, “Being able to participate in the field campaign was a great experience to apply the concepts that we learn in the classroom and to gain a better understanding of how research is conducted.”
Figure 5: Temperature readings moving between the floor and ceiling of a sauna. The temperature difference is over 50 degrees Celsius over just a few meters inside!
Ultimately, the team couldn’t pass up the chance to spend time relaxing in the sauna after long days and nights of intensive operations. On one of the days where the weather outside was not conducive to research, the CASS team decided to test the response of their thermodynamic sensors by using the extreme temperature variations between the sauna and near-freezing outdoor environments. This kind of information is important when processing data because temperature and humidity sensors take time to respond to changes in conditions before providing accurate measurements. This response is usually determined in a lab setting, but the shock of going from the sauna to outdoor conditions still provided useful results. Additionally, the sauna itself provided an interesting environment to study changes in temperature (Figure 5). The hot air from the heater tends to rise to the top of the sauna, while air close to the ground does not heat as much. Utilizing the thermodynamic sensors on one of the UAVs, the CASS team discovered a difference in over 50 degrees Celsius between the floor and ceiling in just 3 meters! While temperature structures like this do not normally exist in nature, it is nonetheless an interesting application of collecting small-scale measurements and characterizing sensor response. “Our capabilities in using UAVs to sample the atmosphere have come such a long way in the past few years, and it was really exciting to see their utility in such a unique environment. I think the future is very bright for this new technology, and it is going to help us learn a lot about the atmosphere.”, said Brian Greene, a graduate research assistant in the School of Meteorology and member of CASS.
Funding for the ISOBAR Project was provided through a research award from the Norwegian Research Council. Additional support for the OU CASS team was made available by the US National Science Foundation (Grant number 1539070 and OU’s Office of the Vice President for Research.)
In Summer 2018, the team will be taking their newfound experience with operations in extreme conditions to the desert of the San Luis Valley as part of the LAPSE-RATE (Lower Atmospheric Process Studies at Elevation – a Remotely-piloted Aircraft Team Experiment) flight week associated with the annual conference of the International Society for Atmospheric Research using Remotely Piloted Aircraft (ISARRA). They will be joined by participants from over 10 institutions, making it one of the largest UAS flight campaigns in the United States. Stay tuned to meteorology.ou.edu for updates on that campaign and an introduction to the CASS team!