Field Report: Measuring Carbon Fluxes with a 1500 Feet Tower and Avoiding Annoying Wildlife
One of the most interesting things we product managers get to do at Picarro is spend time in the field with customers learning how they use our analyzers. This way, we get to experience firsthand the challenges of doing science outdoors in remote locations - challenges like dealing with unpleasant wildlife (for example). Studying fluxes of greenhouse gases in the environment is definitely one of the areas where the full outdoor research experience is mandatory. By fluxes, we mean studying changes in concentrations of gases (like methane, carbon dioxide, etc) in an environment or location and using that to gain insights into ecosystem behavior, climate change, or other areas that our scientist customers closely follow.
Picarro greenhouse gas (GHG) analyzer engineer David Langsam and I got a chance this week to get the full flux experience by accompanying Picarro collaborator and customer, Dr. Ankur Desai from the University of Wisconsin at Madison, to two research tower sites in northern Wisconsin. The two sites we visited were the WLEF Tower in Park Falls, Wisconsin and the nearby Willow Creek Flux Tower. The point of putting instruments on a tower is to measure & correlate changes in the air for a wide range of parameters. WLEF is a 447-meter TV tower utilized by the National Oceanic and Atmospheric Administration, US Forest Service and UW Madison to monitor upwards of 60 molecules including carbon dioxide, methane and sulfur hexafluoride as well as stable isotope ratios (carbon-12, carbon-13, oxygen-16 and oxygen-18) and a host of meteorological parameters like wind speed & direction, humidity, temperature and sunlight intensity. The Willow Creek site has a 30 m tower with equipment dedicated to the study of ecological carbon fluxes. Principal investigators on the Willow Creek site hale from the University of Wisconsin, the University of Minnesota, and Penn State University. Both sites are also part of AmeriFlux and are two of the more than 250 flux sites that contribute to a global flux network coordinated by FLUXNET, an international organization that is pretty much the United Nations of flux research.
So what is a flux tower? Good question. Here's a good description of what a flux tower is. Flux towers play a key role in ecosystem and atmospheric research. Ecologists, atmospheric scientists, hydrologist, meteorologists and other experts use them as a core part of gathering in-depth, local, time-series data for their research. Flux measurements are designed to answer the question of how much energy and mass are exchanged between the biosphere and atmosphere in a region of interest. The height of the tower determines the geographical and geospatial size of the the region of interest. This determination is called a "fetch". A taller tower gives a larger fetch, but at higher elevations measurements lose spatial resolution. While a short tower provides you lots of detailed information, a researcher needs exponentially more towers and equipment to measure a given area. Flux research is complicated because it must strike a balance between these competing principles while taking into account a myriad of ecological, environmental and meteorological factors all while also trying to minimally disturb the ecosystem. Ankur's research is focused on topics that we at Picarro think about a lot. Some of his research focus areas include:
- How are the exchanges of carbon dioxide, water vapor and methane between ecosystems and the atmosphere mediated by land cover change, complex terrain, forest management, and disturbance?
- Can global climate and ecosystem models adequately explain regional carbon exchange in complex regions?
- When do variations in soil moisture and land cover affect the atmospheric boundary layer, dynamics of the hydrologic cycle, cloud formation, and precipitation?
We went out to the WLEF tower with Ankur to help install and test one of our new flux analyzers, which has some neat capabilities. The analyzer can measure the concentration of carbon dioxide, methane, and water 10 times every second (yes, that is 30 concentration measurements every second!). It synchronizes the measurements automatically with wind speed and direction data from a 3-D sonic anemometer. Synchronizing data from different instruments is essential for building accurate models of complex ecosystem behavior. If done manually, synchronization is a time consuming and difficult task made especially tricky because of the high data rates and large diversity of instruments used for flux measurements. Adding the capability to easily match concentration and wind data helps to speed up overall data analysis while reducing the chance for errors. With this analyzer at the tower, Ankur will pull in concentration data that he can incorporate into his micrometeorology models and, ultimately (we hope) use in his published research.
In driving just 30 minutes from WLEF to Willow Creek, we saw clear differences in the ecosystems surrounding the towers. The variability of landscape over such a short distance certainly highlights the level of complexity involved as well as the need for more towers and more measurements. Each ecosystem has its own unique set of interactions depending on the flora, fauna, topography, weather, and many other factors, all of which result in very different carbon fluxes. Despite the hundreds of towers located globally, the vast majority of the earth does not fall inside a flux tower fetch. This makes successful scaling of the flux measurements to regional and global scales for use in modeling and verification of remote sensors a challenging exercise. How well can you estimate the carbon flux in one area by using a flux measurement made at a a different location? How fine of a grid of towers do you need to produce accurate global models? The only clear answer is this - we need a lot more operating flux towers than we currently have.
After visiting the sites, David and I agreed that measuring the world’s carbon fluxes seemed a daunting task, to say the least. And what about the unpleasant wildlife? That would be ticks. Lots of them. At least a dozen tried to hitch a ride back to California with David and I, only to be unceremoniously flung from the car window on the drive back to the airport. Part of the job of being a scientist, I guess.