Observations of the thermodynamic and kinematic state of the atmospheric boundary layer over the San Luis Valley, CO using remotely piloted aircraft systems during the LAPSE-RATE field campaign

In July 2018, the University of Oklahoma deployed three CopterSonde 2 remotely piloted aircraft systems (RPAS) to take measurements of the evolving thermodynamic and kinematic state of the atmospheric boundary layer (ABL) over complex terrain in the San Luis Valley, Colorado. A total of 180 flights were completed over five days, with teams operating simultaneously at two different sites in the northern half of the valley. Two days of operations focused on convection initiation studies, one day focused on ABL diurnal transition studies, one day focused on internal comparison flights, and the last day 5 of operations focused on cold air drainage flows. The data from these coordinated flights provides insight into the horizontal heterogeneity of the atmospheric state over complex terrain as well as the expected horizontal footprint of RPAS profiles. This dataset, along with others collected by other universities and institutions as a part of the LAPSE-RATE campaign, have been submitted to Zenodo (Greene et al., 2020) for free and open access (DOI:10.5281/zenodo.3737087).

pre-programmed mission and was only manually controlled by the operator during landing. Commands were sent to the RPAS over a telemetry link and data collected were streamed back to the ground station where they were displayed on a customized 60 interface that allowed for real-time monitoring. The ground station and RPAS communicated via a 900 MHz Radio (RFD 900+, RFD Design) that has a range of 40 km.
The CopterSonde 2 is outfitted with sensors that enable it to measure atmospheric state variables as it ascends along its flight path (see Table 4 for details). The wind speed and wind direction were calculated indirectly at 10 Hz using the Wind Vane Mode algorithm described in Segales et al. (2020a) which utilizes the roll, pitch, and yaw angles measured with the inertial 65 measurement unit (IMU) on-board the RPAS's autopilot system, the Pixhawk CubeBlack. The pressure was measured at 10 Hz with a MS561 capacitive pressure sensor inside the Pixhawk CubeBlack, which is also utilized for altitude. Atmospheric temperature was measured at 20 Hz with a fast response bead thermistor (International Met Systems). Relative humidity was measured at 10 Hz using the HYT 271 capacitive humidity sensor (Innovative Sensor Technologies). The temperature and humidity sensors were enclosed in a custom sensor scoop that was 3D printed out of polylactic acid (PLA). The sensors were 70 located inside the tubular portion of an L-shaped duct and were mounted in an inverted V configuration. At the base of the duct was a smart fan that was programmed to aspirate the sensors at a rate of 12 m s −1 and was toggled on during ascent at a height of 1.85 m AGL and off during descent at a height of 1.45 m AGL to prevent dust and debris from being pulled into the scoop.
Each scoop was distinguished utilizing an identification code and calibrated prior to the field campaign using the procedure outlined in Greene et al. (2019). Further information regarding considerations for sensor placement, aspiration, and shielding 75 on the CopterSonde can be found in Greene et al. (2018Greene et al. ( , 2019. More on the data quality and statistical performances will be discussed in Section 4.

Flight Strategies
The Preprint. Discussion started: 9 September 2020 c Author(s) 2020. CC BY 4.0 License. is provided in Figure 2, with the inset focusing on the layout of the multiple assets operating at MOFF. The MOFF and NSF A second OU team was deployed to one of three locations depending on the daily objective. For the convection initiation (CI) and boundary layer transition (BLT) study days, the second team set up at K04V. For the cold air drainage study, the team deployed to NSF. Across all three sites, 180 successful flights were completed in support of LAPSE-RATE. Details regarding to the COA provisions, each OU operations area was overseen by a licensed private pilot who assisted with overseeing the airspace and deconflicting RPAS operations from general aviation traffic.
CopterSonde missions were programmed to fly a vertical ascent from the surface to 914 m AGL, utilizing the platforms wind vane mode to continuously orient itself into the wind. This permitted the RPAS to sample the vertical structure of pressure, 120 temperature, humidity, wind speed, and wind direction in a controlled and repeatable manner that minimized influences from the platform itself (Segales et al., 2020a). These flights will be referred to as profiles in subsequent text and tables. These profiles consisted of an automatic takeoff, vertical ascent at a rate of 3.5 m s −1 , loiter for 10 s at the apex of the ascent, and controlled decent to 10 m at a rate of 6 m s −1 . Once the platform completed its decent, it would be brought in for a landing manually.

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Profiles were conducted on a 15-or 30-min cadence depending on the day's primary scientific objective and how rapidly the thermodynamic and kinematic parameters of the ABL were evolving. As the CopterSonde was collocated with CLAMPS at MOFF, RPAS profiles would often coincide with radiosonde launches. When this would occur, the RPAS launch would be held until the balloon cleared the airspace (about 60 s), and then would proceed as normal. Preprint. Discussion started: 9 September 2020 c Author(s) 2020. CC BY 4.0 License. The environment on the morning of 15 July 2018 was rich in moisture with decreasing stability as the day progressed. This made for good conditions to target pre-convective measurements. The low wind shear and weak synoptic flow were conducive for isolated CI. This aided in spatially discerning precursors to CI. Two CASS teams were stationed at MOFF and K04V, approximately 18 km apart, with aircraft OU946 and OU955, respectively. Both teams began flying at 1400 UTC (0900 MDT). and warmer than the ABL below. While a small bias between the two aircraft exists in temperature and specific humidity, the profile shapes and inversion magnitudes are consistent across the platforms. Furthermore, winds throughout the depth of 155 the atmosphere were weak and variable, but still show reasonable agreement between the two aircraft. For a more detailed perspective on the relative accuracy and precision of this dataset, readers are again referred to Barbieri et al. (2019) andBell et al. (2020).

Boundary Layer Transition -18 July 2018
The morning of 18 July 2018, featured weak ambient synoptic-scale weather conditions and clear skies throughout the valley 160 that enabled targeted measurements of the diurnal ABL transition. On this day, the two CASS teams were situated at the MOFF and K04V sites, with operations taking place from 1230-1945 UTC (0630-1345 MDT; Table 3)

Data processing
The data collected by the CopterSondes were processed and quality controlled by CASS after the conclusion of the LAPSE-RATE campaign. The CopterSondes' Pixhawk autopilot system output and store a binary file on an on-board SD card during each flight, which includes logs of the aircraft's attitude angles, GPS positions, accelerations, and readings from the 3 temperature and 3 relative humidity sensors. In this format, the data are equivalent to the United States Department of Energy the course of six days of operation to collect vertical profiles of the thermodynamic and kinematic state of the ABL. This article describes sampling strategies, data collection, platform intercomparibility, data quality and processing, and the dataset's 230 possible applications to convective initiation, drainage flows, and ABL transitions.
The data available from these flights provides measurements of temperature, humidity, pressure, wind speed, and wind direction at a higher spatiotempral resolution in the ABL then many conventional strategies, such as radiosondes, which will significantly contribute to characterizing the ABL within the San Luis Valley during the campaign. The data collected from the operations and platforms described here are uploaded and available for download through the Zenodo data repository 235 (DOI:10.5281/zenodo.3737087).