## 3 Results and Discussion
The positions of the absorption lines for O\({}_{2}\), CO\({}_{2}\) and CH\({}_{4}\) correspond to the ones given in the HITRAN spectral database [54], see Figure 9. We used open source software such as Python, NumPy, SciPy and Matplotlib for data processing and visualization. Graphs of CO\({}_{2}\) and CH\({}_{4}\) concentrations are shown in Figure 10. The shape of the graph corresponds with traffic jams in the observation area. Measurements of greenhouse gases were obtained from the transmittance spectra in Figure 8 by constructing a baseline on the characteristic spectral bands for each substance (6100-6400 cm\({}^{-1}\) for CO\({}_{2}\), 7766-8009 cm\({}^{-1}\) for O\({}_{2}\) and 5980-6010 cm\({}^{-1}\) for CH\({}_{4}\)). The baseline was calculated as a linear function with three points at the boundaries of each interval. Integral concentrations (ppm\(\times\) m) of CO\({}_{2}\) and CH\({}_{4}\) were calculated from the depth of the absorption lines in the recorded spectra. The volumetric concentrations (ppm)  
Figure 7: The scheme of solar reflection measurements in urban conditions: 1—spectrometer; 2—tripod; 3—Rigol DP832 laboratory power sources; 4—laptop. of CO\({}_{2}\) and CH\({}_{4}\) were calculated from their integral concentrations. The obtained values were smoothed by a sinc window function with a half-width of 50 points. The obtained values of CH\({}_{4}\) concentrations correspond to the data from MosEcoMonitoring measuring stations [55] and CO\({}_{2}\) concentrations correspond to the data in [56]. The variations in CO\({}_{2}\) concentration during the day correspond to the data from near-surface air measurements using a Fourier transform spectrometer [57; 58]. The presented results experimentally demonstrate the possibility of measuring greenhouse gas concentrations by reflected solar radiation using an IR Fourier spectrometer. The developed compact, low-resolution FTIR spectrometer is designed to be placed in CubeSat spacecraft for remote measurement of greenhouse gas concentrations. The functional parts of the CubeSat FTIR spectrometer are the same as for the ground-based mockup. The differences are in the mechanical design, for example, the use of special materials with an extended temperature range. To limit the radiation flux, a motorized diaphragm can be installed in the optical system. A diaphragm allows us to change the size of the radiation flux in the range from 1 mm to 27 mm. To ensure functioning in outer space, special heat sinks from electronic circuit boards can be used, special vacuum lubrication of moving parts can be provided and a radiation-resistant element base can be used. The CubeSat FTIR spectrometer will be tested in conditions close to those in outer space. Figure 8: The atmosphere transmittance spectrum measured by the FTIR spectrometer mockup. The spectral bands for O\({}_{2}\) at 7880 cm\({}^{-1}\), CO\({}_{2}\) at 6250 and 6350 cm\({}^{-1}\) and CH\({}_{4}\) at 6024 cm\({}^{-1}\) are shown. Figure 9: The HITRAN and measured transmittance spectra for O\({}_{2}\), CO\({}_{2}\) and CH\({}_{4}\). For the CubeSat FTIR spectrometer, we assume a detection limit of about 1% of the nominal values of CO\({}_{2}\) and CH\({}_{4}\) concentrations in the atmosphere. The precision and accuracy of gas detection and concentration evaluation are determined by the spectral resolution of the device at the level of 2 cm\({}^{-1}\). In the considered measurement range, the main atmospheric components do not have strong absorption lines according to HITRAN [54] and GEISA databases and SPECTRA Spectroscopy Tools [59].