A New Method of Evaluating Gas Fluxes in a Closed Chamber System with Theoretical Consideration for Dynamic Characteristics of a Concentration Sensor

抄録

The accurate determination of gas fluxes in soil-plant-atmosphere systems is crucial for various physio-ecological investigations. The closed chamber method estimates gas fluxes from vegetation and soil by the rate of change in gas concentrations, that is, the first derivatives of the regression functions fit to the measured change in gas concentration. Conventional regression functions, however, can underestimate the actual gas fluxes because these functions do not consider the dynamic characteristics of the concentration sensor (i.e., response lag and dead time). The purpose of this study is to develop a new regression function that can consider the dynamic characteristics of a gas concentration sensor. The newly proposed function was derived theoretically by solving a differential equation of a first-order lag relation between the sensor output and actual gas concentration inside a chamber. Its validity was examined by comparative analysis using CO₂ concentration change measured by slow and rapid-response sensors. The newly proposed function improved the accuracy of flux estimation considerably when applied to the output of a slow-response sensor. The newly proposed function provides a method to evaluate gas fluxes using a low-cost, slow-response sensor in a closed chamber system with acceptable accuracy.