Csat3

Continuous flux measurements with the eddy covariance (EC) technique are performed in 49 m height on the scaffolding tower since July 2014 using an ultrasonic anemometer (CSAT-3, Campbell Scientific Inc., Logan, UT, USA) and an open-path infrared gas analyser (LI-7500, LiCor Inc., Lincoln, NE, USA) for carbon dioxide (CO ${}_2$ ), water vapour (H ${}_2$ O), sensible heat (H) and momentum ( $\tau$ ) fluxes^{88 (link),89 (link)}. The sonic anemometer is directed to west-south-west according to the main wind direction prevailing in the area. High-frequency raw data are acquired with a CR3000 data logger (Campbell Scientific Inc., Logan, UT, USA) and collected, pre-processed and archived with the EDDYMEAS data acquisition module of Eddysoft⁹⁰ . Sampling frequency for wind components, sonic temperature and CO ${}_2$ and H ${}_2$ O concentrations is 20 Hz. Since spring 2016 an additional EC system according to ICOS standards (GILL HS-50, Gill Instruments Ltd., Lymington, UK and LI-7200, LiCor Inc., Lincoln, NE, USA) was installed on the tower in the same height until Oct. 2018 and was moved to 45m height thereafter.

Carbon cycling was measured using seven eddy covariance (EC) towers located within the KW (Figure 1). The towers were located in a series of agricultural fields and restored prairies (see [66 ] for site information). Since these towers are all located in agricultural or grassland sites, they do not represent the landscape as a whole, however, they can still provide some information about the magnitude and timing of C fluxes in this region.
Each tower was equipped with an infrared gas analyzer (LI-7500, LI-COR Biosciences, Lincoln, NE, USA) and a 3D sonic anemometer (CSAT3, Campbell Scientific Inc., Logan, UT, USA), with sensor heights 1.5–2.0 m above canopy heights [67 ]. Fluxes were processed following Ameriflux guidelines, with 30-min average fluxes (i.e., net ecosystem production, NEP) computed with EdiRe [68 ] and then gap filled and partitioned into gross primary production (GPP) and ecosystem respiration using REddyProc [69 ]. Flux data was u* filtered [70 ], with an average u* threshold of 0.11 m s⁻¹, removing 25.3% of the data.

During the flowering period, the microclimate in the field was measured using an eddy covariance system. The wind vector was determined using a three-dimensional sonic anemometer (CSAT-3, Campbell Scientific, USA). The tilt correction was done to make the average wind speed in the crosswind and vertical direction zero. Global radiation was measured by LI-200×(LI-COR Inc., USA), air temperature and relative humidity was measured by HMP155A (Vaisala Corporation, Finnish), and wind speed and direction were measured by 010 C and 020 C (Met One Instruments, Inc., USA). These sensors were all installed in the field at the height of 2.0 m from the ground. They were collected and stored by CR3000 Datalogger (Campbell Scientifics, USA). The sampling frequency was 1 Hz, and the average value was stored every 30 min. Weather phenomena were recorded manually.

Carbon fluxes and micrometeorological data were obtained by 40 m high flux tower equipped with open-path eddy-covariance system (OPEC), atmospheric profile system (APS), and gradient micrometeorological system (GMS). The OPEC was deployed at 38 m according to the height of the forest stand canopy, while the APS and GMS were deployed at seven levels (1, 7, 11, 17, 23, 30, and 38 m) on both sides of the tower arm. The OPEC comprised a 3-D sonic anemometer (CSAT3, Campbell Scientific, USA) and an open-path CO₂/H₂O analyzer (Li-7500, Li-COR Biosciences, USA). The APS was deployed to obtain real-time CO₂ and H₂O concentration by AP200(Campbell Scientific, USA). The GMS included temperature and humidity sensor (HMP155, Vaisala, Finland), wind speed sensor (WindSonic, Gill Instruments, UK), 4-component net radiometer (CNR4, Campbell Scientific, USA), soil moisture and temperature profile sensor (SoilVUE10, Campbell Scientific, USA) and soil heat flux sensor (HFP01, Hukseflux, Netherlands) at depths of 5, 10, 20, 30, 40 and 50 cm. Systematic observation data, including physical quantities such as CO₂ flux at 10 Hz, friction wind speed, and other relevant physical quantities, as well as 30-min averaged conventional meteorological information, were stored using a CR1000 data collector (Campbell Scientific, USA).

Demonstrative sUAS flights were performed at Christman Airfield located in Fort Collins, Colorado. To experiment with plume detection by the sUAS methane sensor, we employed a controlled release setup to provide methane plumes of known mass flow. The setup included a cylinder of chemically pure (99.5%) methane delivered with a mass flow controller (Sierra SmartTrak 50). The final release point (mass flow controller outlet) was at a height of 1 meter above the ground. A weather station (Campbell Scientific, CR1000 and NL115) with ultrasonic anemometer (Campbell Scientific, CSAT3) was used to simultaneously record time series of wind speed amplitude (20 Hz rate). Plumes could be captured at varying distances up to ~500 meters from the source. Flight paths around the emission point were adjusted depending on wind magnitude and direction. The controlled release setup is shown in Figure 3.

Since August 2012 at the center of core experimental area, the CO₂ fluxes were detected using an CO₂/H₂O analyzer (LI‐7500, Li‐Cor Inc., Lincoln, NE, USA) mounted at 2 m above the soil surface, and a 3D sonic anemometer (CSAT3, Campbell Scientific Inc., Logan, UT, USA). A CR3000 datalogger (Campbell Scientific Inc.) was used to collect and record 10‐Hz and half‐hour mean fluxes data.
The photosynthetically active radiation was measured using a LI190SB (Licor Inc.), and net radiation (R_n) was determined using a CNR‐1 (Kipp & Zonen Inc., The Netherlands). A HMP45C (Campbell Scientific Inc.) was used to detect air relative humidity and temperature. A 52203 rain gauge (RM Young Inc., USA) was used to determine rainfall. Soil volumetric water moisture (SWC) and temperature at one soil profile (5, 20, and 50 cm depths) were recorded with CS616‐L TDR probes (Campbell Scientific Inc.) and 105T thermocouples (Campbell Scientific Inc.), respectively. Three HFT‐3 plates (Campbell Scientific Inc.) at 5 cm soil depth were used to detect soil heat flux (G). The half‐hour values of all above variables were stored by CR1000 dataloggers (Campbell Scientific Inc.).