Application of the variance method for CO2 flux to aircraft measurement

We investigated that how the variance method can be used to estimate CO2 flux from aircraft data. The accuracy of the relatively simple variance method was estimated by comparison with the conventionally used eddy covariance method based on tower measurement data. The tower data were collected in a Japanese Larch forest and in a very flat Siberian forest during the summer. CO2 flux by variance method corresponded well with the eddy covariance flux within 30% when ζ less than -0.04. The CO2 flux was measured by variance method with small aircraft over the forest by means of a closed-path CO2 analyzer (Li6262; Li-COR, USA) and very thin thermocouple (T-type with 0.025mm diameter). The advantage of this system is very easy installation without any modification to the aircraft body. According to the tower data analysis, this system can be measured enough frequency response to estimate CO2 flux over the forest by aircraft. Under fine weather conditions, the aircraft CO2 fluxes estimated by variance method were sometimes in close agreement with the tower CO2 fluxes estimated by eddy covariance and CBL budget methods. These results suggest that the variance method could offer a portable and valid way to measure spatial distribution of local surface CO2 flux and regional scale flux.