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Experimental Test of Density and Energy-Balance Corrections on Carbon Dioxide Flux as Measured Using Open-Path Eddy Covariance

^a Dep. of Agron., Kansas State Univ., Manhattan, KS 66506
^b Dep. of Soil and Crop Sci., Texas A&M Univ., College Station, TX 77843

View larger version (36K): [in a new window]   Fig. 1. Net radiation (Rn), sensible heat flux (H), and soil heat flux (G) at the parking lot used to test the open-path eddy covariance instrumentation. Soil heat flux was calculated as a residual after assuming latent heat flux was negligible, G = -(Rn - H).

View larger version (22K): [in a new window]   Fig. 2. Comparison of sonic- and thermocouple-derived measurements of air temperature. Each point is a 30-min average.

View larger version (23K): [in a new window]   Fig. 3. Comparison of sonic- and thermocouple-derived measurements of sensible heat fluxes as obtained by eddy covariance. Each point represents a 30-min flux measurement.

View larger version (37K): [in a new window]   Fig. 4. Eddy covariance measurements of CO2 flux above a parking lot for 7 d in July 2002. Shown are uncorrected raw measurements and the same data after density corrections have been applied. Actual fluxes of CO2 from the surface were approximately 0.04 mg m-2 s-1 (dashed line). Downward fluxes are negative; upward fluxes are positive.

View larger version (21K): [in a new window]   Fig. 5. Error in the 30-min measurements of CO2 flux plotted against the corresponding sensible heat flux.

View larger version (40K): [in a new window]   Fig. 6. Eddy covariance measurements of latent heat flux above a parking lot for 7 d in July 2002. Shown are uncorrected raw measurements and the same data after density corrections have been applied. Actual latent heat fluxes were assumed to be zero. Downward fluxes are negative; upward fluxes are positive.

View larger version (36K): [in a new window]   Fig. 7. Eddy covariance measurements of CO2 fluxes from (a) tallgrass prairie and (b) cedar forest, both located near Manhattan, KS. Shown are uncorrected raw measurements and the same data after density corrections have been applied. Downward fluxes are negative; upward fluxes are positive.

View larger version (23K): [in a new window]   Fig. 8. Sum of sensible and latent heat fluxes (H + E) vs. available energy (Rn - G) for tallgrass prairie and a cedar forest. Data were collected between day of year 168 and 174, 2002; each point is a 30-min measurement.