Featured Expert: Dr. Stefan Metzger

Stefan Metzger, Principal Research Scientist, Surface-Atmosphere Exchange

December 2017

Each day, NEON’s surface-atmosphere exchange sensors generate billions of data points. Stefan Metzger’s job is to turn those data points into information that is useful for the research community and societal decision making.

As a lead on the NEON surface-atmosphere exchange team, he is responsible for the development of algorithms that create publicly available data products. Also known as “flux”, surface-atmosphere exchange quantifies how much heat, water, and other trace gases such as carbon dioxide are transported between all things living and nonliving on the ground and the air above. Eddy-covariance is one of the most direct methods to determine this surface-atmosphere exchange: at NEON, 47 terrestrial field sites are equipped with sensors on atmospheric flux towers that gather data on wind, temperature and gas concentrations at different vertical levels. The resulting data products help researchers better understand how heat and gasses are transferred between soil, plants, and the atmosphere; and the balance of energy and gasses going into and out of the atmosphere. The socio-economic applications of the data range from vegetation and water adaptation strategies to severe weather forecasting and are central to our understanding of sustainable future scenarios.

Sensor data at the sites are collected up to 40 times per second across more than 100 channels. Each day, this generates millions of data points for each of the 47 terrestrial field sites. Digesting and processing this data requires advanced analytics capabilities: together with his team, Stefan created algorithms that consolidate the raw data into products with time resolutions of minutes to hours. These present the findings in ways that are meaningful to researchers and are central to answering a broad range of critical questions facing research and society.

Stefan’s next phase of research and development focuses on the integration of the automated sensor data with other data sources, including remote sensing data generated by NEON as well as other agencies such as NASA. He explains, “The NEON flux towers give us a lot of depth of information at a local level, but their spatial coverage is very limited—on the order of hectares. With airborne and satellite data one can get close to global coverage, but it is delivered in square kilometer increments and intermittent in time. These differences in the data characteristics gathered by the different systems make it difficult to join their information in truly synergistic ways.” Stefan is currently working on a project to combine in-situ and remote sensing data so that researchers are able to tap into the full complement of available information.

This work resulted in the paper "Surface-atmosphere exchange in a box: Making the control volume a suitable representation for in-situ observations," in Agricultural and Forest Meteorology. A follow-up paper led by graduate student K. Xu explores the practical application and impact of this novel data fusion concept.

Stefan joined NEON as a postdoctoral scholar in 2011. At that time he was responsible for the scientific design of the eddy-covariance sensor systems that are collecting flux data today. Starting in 2014, he continued his work as a Staff Scientist, designing the data processing components of the system. This work resulted in the open-source, portable, reproducible and community-extensible eddy4R software. Since 2016 he has been leading NEON’s surface-atmosphere exchange team together with his colleague Hongyan Luo. The team, which currently consists of five scientists and 10 software engineers, delivers NEON’s eddy-covariance data processing pipeline.

Stefan holds a Ph.D. in Micrometeorology from Bayreuth University in Germany and a M.Sc. in Geoecology, and Chinese Language and Culture. His Ph.D. thesis focused on the use of weight-shift microlight aircraft for measuring the turbulent exchange over complex terrain. During both his M.Sc and Ph.D. studies he spent extended periods of time in China, where he worked with the Chinese Academy of Sciences on field measurements in Tibet and research flights in Inner Mongolia, among others. In addition to his work at NEON, he is an Adjunct Assistant Professor at the University of Wisconsin, Department of Atmospheric and Oceanic Sciences.

As the NEON project progresses, Stefan sees a need for continued work in harmonizing and synergizing data products across networks for the study of biogeochemistry, weather, and climate. “There is a lot of data out there, but it’s not easy to compare and use together to draw meaningful conclusions,” he says. A first step is the inclusion of NEON’s surface-atmosphere exchange data products in the AmeriFlux network of the Americas, and its global umbrella network, FLUXNET. “Moving forward, one key will be learning how to use data from various systems and networks more effectively instead of relying on more and more equipment in the field alone.”