Testing a new CH4, and CO2, flux instrument for the University of Wyoming King Air Platform

Abstract:

Green house gases’ fluxes in diverse areas such as forests, grasslands, wetlands and arctic regions have become more important as the surface-atmosphere exchange rates of GHG’s are expected to respond to a changing climate. These fluxes can be determined using the eddy covariance method. Eddy covariance data from flux towers represents a comparatively local homogeneous source areas by each tower. Meanwhile, there is a scarcity of eddy covariance sites in vast regions of interest, which can be accessible to aircraft flux measurement platforms. Moreover, the instantaneous picture of turbulent field which is provided by aircraft measurements is not prone to temporal trends and non-stationary effects. The aim of this research is to develop an aircraft eddy covariance system for the University of Wyoming King Air Research Aircraft equipped with a 10 Hz Picarro CO₂/CH₄ analyzer. Test flights to collect eddy covariance measurements of CH₄ and CO₂ were performed above the Pawnee National Grassland, located in northeastern Colorado. These test flights were designed to test the limits of the instrument and compare the performance to available comparable technology, such as the on-board LICOR 7500 CO₂ analyzer. The comparison also put the susceptibility of the new mounted instruments to cabin pressure-altitude fluctuations and other probable design-based artifacts under scrutiny. These flights probed the effects of flight speed, flight altitude and transect length on the calculated flux and uncertainty. In addition to applying the eddy covariance technique, different spectral analysis methods are explored for the data obtained from the test flights. We applied a wavelet spectral analysis to the high-frequency signals to improve spatial discretization of the recorded fluxes. The metrics on the performance of this new flux system are reported and how it may be used in different environments is discussed.