Compensation for the Systematic Error of Spectral Measurements of the Background Concentration of Methane in the Earth's Atmosphere

We investigate the error in developing a technique for measuring the background concentration of methane by the passive location method using solar radiation as a source. Background concentration of methane is measured along three separate trajectories in a region northeast of Moscow. The first route passes through an urbanized area with developed infrastructure, industry and high population density; the second and third routes pass through areas with a lower population density and buildings, and have many forests and reservoirs. When processing measurement results, it was found that, along with random errors, it is necessary to take into account the systematic error due to the influence of external factors on measuring the methane background concentration during sounding under small angles to the horizon, when the path length noticeably increases. It is shown that such influencing factors can include the scattering of light by aerosols and other impurity particles in the atmosphere. Compensation adjustments have been made which reduced the systematic error to almost zero. A monitoring technique has been proposed that makes it possible to obtain a relative error in units of percent when measuring the background concentration of methane over a long duration. The results of the performed measurements are consistent with the results of global measurements and confirm the growth in the background concentration of methane in the Earth's atmosphere in recent years.