Determination of scalar fluxes over Mediterranean vegetation

The surface renewal (SR) method for estimating fluxes from canopies involves high frequency measurements of scalar parameters. The high frequency data are analyzed for ramp-like characteristics and the amplitude and inverse ramp frequency are used in basic energy or mass conservation equations to estimate fluxes. In previous papers, good results were reported for estimating sensible (H) flux density over a variety of vegetated surfaces. The results for latent heat (LE) flux density and carbon dioxide flux density (Fc) over an old-growth forest were less clear but show promise. In this paper, we report on data collected over Mediterranean shrub vegetation. Data were collected near the west coast of Sardinia, Italy. High frequency (10 Hz) wind speed, temperature, humidity, and carbon dioxide fluctuations were recorded using a CSAT3 sonic anemometer and Licor 7500 infrared gas analyzer mounted above the canopy top. Estimates of eddy covariance (EC) LE and Fc were corrected for density fluctuations. The same high frequency data were used to determine H, LE, and Fc using the surface renewal method and the results were compared with EC measurements. The SR method provided a simple, low-cost method to estimate scalar fluxes without the need to measure stability or wind speed. Therefore, the SR method can be used to estimate scalar fluxes during periods with missing data or when more expensive equipment is unavailable. The methodology and results of our experiments will be presented.