In this part of the course we focus on the instrumentation and data processing techniques of surface flux towers. These towers typically use the so-called eddy covariance technique to measure sensible and latent heat fluxes as well as other turbulence quantities. To close the surface energy balance, additional instruments such as net radiation and soil temperature sensors are typically also installed at such towers. For ecosystem studies, the sites may be equipped with additional sensors to measure e.g. CO2 or other trace gas fluxes.
As you will see eddy-covariance measurements require expensive instrumentation, intensive post-processing, and the data must be carefully screened. In the four lectures, we cannot cover everything – there are entire books (see the references) devoted to eddy-covariance measurements. Instead, the objective is to introduce important data processing steps and quality assurance checks. It is important that you don’t treat flux measurement systems as black boxes and that you are aware of the limitations of these systems if you work with flux data.
References:
Books:
Aubinet, M., T. Vesala, and. D. Papale (Eds.), 2012. Eddy Covariance. A Practical Guide to Measurement and Data Analysis. 438p. Springer. https://www.springer.com/gp/book/9789400723504
Foken, T., 2017. Micrometeorology. 362p. Springer. https://www.springer.com/gp/book/9783642254390
Lee X., W Massman, B. Law, 2005. Handbook of Micrometeorology. 250p. Springer. https://www.springer.com/gp/book/9781402022647
Some Selected Journal Articles:
Finnigan, J.J., Clement, R., Malhi, Y. et al. A Re-Evaluation of Long-Term Flux Measurement Techniques Part I: Averaging and Coordinate Rotation. Boundary-Layer Meteorology 107, 1–48 (2003). https://doi.org/10.1023/A:1021554900225
Finnigan, J.J. A Re-Evaluation of Long-Term Flux Measurement Techniques Part II: Coordinate Systems.Boundary-Layer Meteorology 113, 1–41 (2004). https://doi.org/10.1023/B:BOUN.0000037348.64252.45
Kljun, N., Calanca, P., Rotach, M. W., and Schmid, H. P.: A simple two-dimensional parameterisation for Flux Footprint Prediction (FFP), Geosci. Model Dev., 8, 3695-3713, 2015, https://gmd.copernicus.org/articles/8/3695/2015/
Leuning, R., E. van Gorsel, W. J. Massman, P. R. Isaac, 2012. Reflections on the surface energy imbalance problem, Agricultural and Forest Meteorology, Volume 156, pp. 65-74, https://doi.org/10.1016/j.agrformet.2011.12.002
Massman, W.J. and X. Lee, 2002. Eddy covariance flux corrections and uncertainties in long-term studies of carbon and energy exchanges,
Agricultural and Forest Meteorology, Volume 113, Issues 1–4, pp. 121-144, https://doi.org/10.1016/S0168-1923(02)00105-3 .
Mauder, M., M. Cuntz, C. Drüe, A. Graf, C. Rebmann, H. P. Schmid, M. Schmidt, R. Steinbrecher, 2013. A strategy for quality and uncertainty assessment of long-term eddy-covariance measurements, Agricultural and Forest Meteorology, Volume 169, pp. 122-135, https://doi.org/10.1016/j.agrformet.2012.09.006 ).
Mauder, M., Foken, T. & Cuxart, J. Surface-Energy-Balance Closure over Land: A Review.Boundary-Layer Meteorol 177, 395–426 (2020). https://doi.org/10.1007/s10546-020-00529-6 .
Wilczak, J.M., Oncley, S.P. & Stage, S.A. Sonic Anemometer Tilt Correction Algorithms. Boundary-Layer Meteorology 99, 127–150 (2001). https://doi.org/10.1023/A:1018966204465
Recorded Lectures and Other Resources:
Eddy Covariance Measurements – Introduction
Link to a Webinar about Eddy Covariance Measurements
Campbell Scientific Eddy Covariance Webinar
Please watch this recorded webinar by Campbell Scientific (CSI). It provides information about important siting considerations for eddy-covariance measurements and also discusses the pros and cons of open vs. closed path gas analyzers. I realize that it may seems strange to ask you watch a webinar of a vendor but it really provide a nice intro to important topics and CSI is one of the prime vendors for meteorological instrumentation. This is not a promotion of their products and I and definitely not getting paid by CSI for linking their materials here, it is simply using a good educational resource.
Link to an Online Footprint Model
At the linked website, you can use a 1D online footprint tool for quick estimates and also sign-up to download a 2D-footprint estimation tool. These tools are based on the paper by Kljun et al (2015) which is included in the reference list above.