Application of an alternative method to derive reliable estimates of nighttime respiration from eddy covariance measurements in moderately complex topography

Abstract. Estimating evaporation is important when managing water resources and cultivating crops. Evaporation can be estimated using land surface heat flux models and remotely sensed land surface temperatures (LST), which have recently become obtainable in very high resolution using lightweight thermal cameras and Unmanned Aerial Vehicles (UAVs). In this study a thermal camera was mounted on a UAV and applied into the field of heat fluxes and hydrology by concatenating thermal images into mosaics of LST and using these as input for the two-source energy balance (TSEB) modelling scheme. Thermal images are obtained with a fixed-wing UAV overflying a barley field in western Denmark during the growing season of 2014 and a spatial resolution of 0.20 m is obtained in final LST mosaics. Two models are used: the original TSEB model (TSEB-PT) and a dual-temperature-difference (DTD) model. In contrast to the TSEB-PT model, the DTD model accounts for the bias that is likely present in remotely sensed LST. TSEB-PT and DTD have already been well tested, however only during sunny weather conditions and with satellite images serving as thermal input. The aim of this study is to assess whether a lightweight thermal camera mounted on a UAV is able to provide data of sufficient quality to constitute as model input and thus attain accurate and high spatial and temporal resolution surface energy heat fluxes, with special focus on latent heat flux (evaporation). Furthermore, this study evaluates the performance of the TSEB scheme during cloudy and overcast weather conditions, which is feasible due to the low data retrieval altitude (due to low UAV flying altitude) compared to satellite thermal data that are only available during clear-sky conditions. TSEB-PT and DTD fluxes are compared and validated against eddy covariance measurements and the comparison shows that both TSEB-PT and DTD simulations are in good agreement with eddy covariance measurements, with DTD obtaining the best results. The DTD model provides results comparable to studies estimating evaporation with similar experimental setups, but with LST retrieved from satellites instead of a UAV. Further, systematic irrigation patterns on the barley field provide confidence in the veracity of the spatially distributed evaporation revealed by model output maps. Lastly, this study outlines and discusses the thermal UAV image processing that results in mosaics suited for model input. This study shows that the UAV platform and the lightweight thermal camera provide high spatial and temporal resolution data valid for model input and for other potential applications requiring high-resolution and consistent LST.

Download Full-text

Area-Averaged Surface Fluxes Over the Litfass Region Based on Eddy-Covariance Measurements

Boundary-Layer Meteorology ◽

10.1007/s10546-006-9052-x ◽

2006 ◽

Vol 121 (1) ◽

pp. 33-65 ◽

Cited By ~ 86

Author(s):

Frank Beyrich ◽

Jens-Peter Leps ◽

Matthias Mauder ◽

Jens Bange ◽

Thomas Foken ◽

...

Keyword(s):

Eddy Covariance ◽

Surface Fluxes ◽

Eddy Covariance Measurements

Download Full-text

Eddy Covariance Measurements On Mountain Slopes: The Advantage Of Surface-Normal Sensor Orientation Over A Vertical Set-Up

Boundary-Layer Meteorology ◽

10.1023/a:1002660521017 ◽

2000 ◽

Vol 96 (3) ◽

pp. 371-392 ◽

Cited By ~ 37

Author(s):

Peter Geissbühler ◽

Rolf Siegwolf ◽

Werner Eugster

Keyword(s):

Eddy Covariance ◽

Surface Normal ◽

Sensor Orientation ◽

Eddy Covariance Measurements ◽

Set Up

Download Full-text

Near-zero methane emission from an abandoned boreal peatland pasture based on eddy covariance measurements

PLoS ONE ◽

10.1371/journal.pone.0189692 ◽

2017 ◽

Vol 12 (12) ◽

pp. e0189692 ◽

Cited By ~ 4

Author(s):

Mei Wang ◽

Jianghua Wu ◽

Junwei Luan ◽

Peter Lafleur ◽

Huai Chen ◽

...

Keyword(s):

Eddy Covariance ◽

Methane Emission ◽

Eddy Covariance Measurements

Download Full-text

Mapping the aerodynamic roughness of the Greenland ice sheet surface using ICESat-2

10.5194/egusphere-egu21-2136 ◽

2021 ◽

Author(s):

Maurice van Tiggelen ◽

Paul C.J.P. Smeets ◽

Carleen H. Reijmer ◽

Bert Wouters ◽

Jakob F. Steiner ◽

...

Keyword(s):

Eddy Covariance ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Elevation ◽

Spatiotemporal Variability ◽

Atmospheric Models ◽

Laser Altimeter ◽

Eddy Covariance Measurements ◽

Aerodynamic Roughness

The roughness of a natural surface is an important parameter in atmospheric models, as it determines the intensity of turbulent transfer between the atmosphere and the surface. Unfortunately, this parameter is often poorly known, especially in remote areas where neither high-resolution elevation models nor eddy-covariance measurements are available.In this study, we take advantage of the measurements of the ICESat-2 satellite laser altimeter. We use the geolocated photons product (ATL03) to retrieve a 1-m resolution surface elevation product over the K-transect (West Greenland ice sheet). In combination with a bulk drag partitioning model, the retrieved surface elevation is used to estimate the aerodynamic roughness length (z0m) of the surface.We demonstrate the high precision of the retrieved ICESat-2 elevation using co-located UAV photogrammetry, and then evaluate the modelled aerodynamic roughness against multiple in situ eddy-covariance observations. The results point out the importance to use a bulk drag model over a more empirical formulation.The currently available ATL03 geolocated photons are used to map the aerodynamic roughness along the K-transect (2018-2020). We find a considerable spatiotemporal variability in z0m, ranging between 10&#8722;4 m for a smooth snow surface to more than 10&#8722;1 m for rough crevassed areas, which confirms the need to incorporate a variable aerodynamic roughness in atmospheric models over ice sheets.

Download Full-text

On the way to realistic large eddy simulations – A comparison of virtual measurements with CHEESEHEAD19 field measurements

10.5194/egusphere-egu21-2132 ◽

2021 ◽

Author(s):

Luise Wanner ◽

Sreenath Paleri ◽

Johannes Speidel ◽

Ankur Desai ◽

Matthias Sühring ◽

...

Keyword(s):

Energy Balance ◽

Eddy Covariance ◽

Field Measurements ◽

Transport Processes ◽

Large Eddy Simulations ◽

Surface Model ◽

Closure Problem ◽

Energy Balance Closure ◽

Large Eddy ◽

Eddy Covariance Measurements

Large-eddy simulations are useful tools to study transport processes by mesoscale structures in the atmospheric boundary layer, since in contrast to single-tower eddy covariance measurements, they provide not only temporally but also spatially highly resolved information. Therefore, they are well suited to study the energy balance closure problem, for which the mesoscale transport of latent and sensible heat, triggered by heterogeneous ecosystems, is suspected to be a major cause. However, this requires simulations that are as realistic as possible and thus allow a comparison of real measurements in the field and virtual measurements in the simulation. During the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors (CHEESEHEAD) experiment in the summer of 2019, a heterogeneous 10x10 square km domain was intensively sampled across scales. This data offers a unique possibility to set up large-eddy simulations with realistic surface heterogeneity. We use PALM to simulate two days and an area of 40 by 40 square kilometers incorporating the CHEESEHEAD site. The large scale atmospheric forcings to inform the boundary conditions are determined from the NCEP HRRR product. As the lower boundary condition, we use a soil and land-surface model coupled with a plant-canopy model, which we adapt to the CHEESEHEAD area based on ground-based and airborne measurements of plant physiological data. In this study, we investigate how well the simulations match with real measurements by comparing simulated profiles and virtual tower measurements with field measurements from radiosonde ascents, lidar measurements of three-dimensional wind and water vapor, eddy-covariance measurements from the 400 meter tower in the center of the study domain, as well as from typical eddy-covariance stations distributed through the study area. This way, we investigate how realistic the simulations actually are and to what extent the knowledge gained from them concerning the energy balance closure problem can be transferred to field measurements.

Download Full-text