An attenuated eddy covariance method for latent heat flux measurements

An attenuated eddy covariance (AEC) method is proposed, combining the use of a relatively robust three-dimensional sonic anemometer and a ventilated capacitive hygrometer-thermometer (CHT). The CHT is able to resolve a large enough frequency region of the water vapor density turbulent fluctuations to allow corrections for its limited time response in the inertial subrange of the vertical velocity-humidity cospectrum. This approach is often called the "band-pass covariance method.'' In the present work we propose a technique in which the covariance between the vertical velocity and water vapor density fluctuations is calculated directly in the time domain (as in the standard eddy covariance technique) and then corrected for the effects of wind velocity and sensor temperature. This technique has been tested with the capacitive sensor "uncapped'' and "capped'' and in both cases compares well (RMSE <= 23 W m(-2)) with eddy covariance measurements using fast response hygrometers.