## 1 Introduction
A study focusing on the monitoring and modeling aspects in the CCS Total pilot plant on Lacq-Rousse, France, shows that the soil CO\({}_{2}\) concentration was negatively correlated with changes in the piezometric level [37]. Specifically, the fluctuation is caused by the CO\({}_{2}\) dissolution or release process by the perched water table acting as a pump. There was also a strong indication of the seasonal condition affecting the variability of the CO\({}_{2}\) concentration in the soil [37]. Variation of subterranean CO\({}_{2}\) within the depth of 1.5 m was predominantly caused by pressure variations instead of biological or wind influences [38]. However, it is still uncertain whether these relationships exist in temperate forest ecosystems, which plays a significant role in carbon exchange through the biological cycle. The temperate forest ecosystem is also widely known as biologically active, storing a large quantity of soil organic carbon and a deep root system. However, such studies cannot be conducted solely in the laboratory because the natural soil profile mostly consists of active Rhiz-producing and consuming methane, plant-soil interactions, and spatial interaction [32]. The monitoring should be performed in long-term continuous monitoring with short hourly intervals to construct a reliable baseline of natural gas exchange, study its transport and production, and to better understand the influence of short-term events [6]. However, this approach has been considered economically unfeasible and complex. Therefore, there is a strong need to develop an economical and robust continuous soil gas measurement that requires low energy input and does not need complex maintenance. It can be complemented by automatic data transfer. Measurement of the gas concentration using the low-resolution FTIR (Fourier-transform infrared spectroscopy) requires a calibration procedure by characterizing all of the spectrophotometer's instrumental line shape [39]. The chemical functional groups that absorb fundamental bands located at 2350 cm\({}^{-1}\) for CO\({}_{2}\) and a combination of 1400-1200 cm\({}^{-1}\) and 3200-2800 cm\({}^{-1}\) for CH\({}_{4}\) can be used to quantify their concentration. FTIR technique takes into account the fact that the majority of the molecules absorb IR radiation, and the degree of the absorption is proportional to the concentration of the molecule. There are some significant conveniences in using FTIR including, (i) few optical elements; (ii) no need slits to attenuate radiation; (iii) outstanding stability and sensitivity (iv) high-speed data collection. FTIR also offers various benefits, such as near real-time operation, low maintenance, low cost, and simple structural specification [40; 41]. Nonetheless, in term of its operation, FTIR spectroscopy has some limitations as follows: (i) This spectrometry can only be used for heteronuclear gases; (ii) it is considered as low resolution (1 cm\({}^{-1}\)) that requires specific laboratory calibration for every single gas; (iii) it is superimposed by the presence of impurities [5; 42], (iv) its implementation on long-time span in the field is difficult due to the required energy power. The main objectives of this study are three-fold; (i) To develop and field test a specific flow system equipped with a membrane probe to continuously measure the soil gas concentration and auxiliaries data; (ii) to combine borehole with micrometeorological monitoring; (iii) to understand the main physical drivers of gas exchange in a deep soil layer (\(-6\) m) and a shallow soil layer (\(-1\) m) regardless of the water saturation conditions. In this paper, both the gas calibration procedure in the laboratory are described, and the observational setup of the measurement campaign, aspects of the data analysis, and analysis of the recorded time series of soil CO\({}_{2}\) and CH\({}_{4}\) concentration are shown.