Verification of flux measurement using relaxed eddy accumulation

Businger and Oncley (1990; Flux measurement with conditional sampling, J. Atmos. Ocean Technol.7, 349–352) proposed a method to measure fluxes of scalar quantities by determining the mean concentration difference between air samples collected selectively during updrafts. This method has been tested for carbon dioxide over a growing cotton field where the fluxes were large. Simultaneous direct flux measurements were made using the eddy-correlation technique. These two techniques gave fluxes which were mostly within 20% on one of the two experiment days; however, the other day had cases with large differences. These differences are suspected to have been caused by a failure of the infra-red absorption sensor used to make the fast carbon dioxide measurements for the eddy-correlation technique.