Study On CO₂ Concentration Denoising Of Soil Respiration Monitor

The self-developed soil respiration monitor can effectively avoid the drawbacks of traditional instruments.However,the diffusion of CO₂ in the gas chamber is easily affected by the number and quality of sensors in the external environment and soil monitors,resulting in inaccurate measurement of soil respiration.For the self-developed soil respiration monitor,it is difficult to accurately monitor the time series of CO₂ concentration on the soil surface.This paper uses Fick's second law to describe the concentration distribution of diffusion material in the diffusion process with time,fitting the time series of CO₂ concentration at the surface location of the soil.But the data quality is unsatisfactory.Therefore,this paper proposes a method combining Fick's second law and wavelet packet transform to denoise the soil CO₂ concentration time series.Firstly,Fick's second law is used to fit the time series of soil CO₂concentration at the surface.Secondly,the law of time-varying soil CO₂ changes with height in the gas chamber is calculated by Fick's second law.The time series of soil CO₂ concentration at various heights is set at the surface.Finally,the denoising analysis of the unsteady soil CO₂ concentration time series is carried out by wavelet packet transform.As a comparison,Fick's law and the first Fick's law wavelet packet transform method are also used.The experimental results show that the algorithm is similar to the general method in terms of mean value.However,in terms of signal-to-noise ratio,root mean square error and slope distance,the time series of soil CO₂ concentration calculated by the algorithm is obviously better than that calculated by the traditional method.The obtained results show that the time series of CO₂ concentration at any position in the gas chamber can be accurately calculated by the algorithm.At the same time,the soil CO₂ concentration in the early,middle and late periods was measured in the study area.After denoising,the soil carbon flux calculated using Fick's first law is about 10%lower than the carbon flux measured by LI-8100.The algorithm not only accurately calculates the CO₂ concentration time series at any position in the open gas chamber at any time,but also obtains the soil carbon flux similar to LI-8100 by calculating the time series after processing.