# UVsq-Sat NG, a New CubeSat Pathfinder for Monitoring Earth Outgoing Energy and Greenhouse Gases
## 4 Methodology for Determining ERB and GHGs with Uvsq-Sat NG
\begin{table}
\begin{tabular}{l l l l l l l} \hline \hline  & \multicolumn{6}{c}{**Uvsq-Sat NG NIR Spectrometer Spectral Resolution: 1 nm**} \\ \hline SNR & 50 & 100 & 250 & 500 & 1000 & 2000 & 5000 \\ \hline CO\({}_{2}\) [ppm] & 10.998 & 5.602 & 2.204 & 1.130 & 0.575 & 0.277 & 0.110 \\ CH\({}_{4}\) [ppb] & 125.028 & 66.209 & 25.245 & 12.302 & 6.625 & 3.108 & 1.294 \\ O\({}_{2}\) [Ratio] & \(11.024\times 10^{-3}\) & \(5.921\times 10^{-3}\) & \(2.433\times 10^{-3}\) & \(1.165\times 10^{-3}\) & \(0.636\times 10^{-3}\) & \(0.299\times 10^{-3}\) & \(0.120\times 10^{-3}\) \\ H\({}_{2}\)O [cm] & \(4.746\times 10^{-3}\) & \(2.271\times 10^{-3}\) & \(0.877\times 10^{-3}\) & \(0.441\times 10^{-3}\) & \(0.207\times 10^{-3}\) & \(0.114\times 10^{-3}\) & \(0.045\times 10^{-3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Uncertainties of atmospheric gas concentrations (1–Sigma) for various data retrievals based on different instrumental characteristics. Figure 7: Restitution of the concentration of gases observed via the Uvsq-Sat NG NIR Spectrometer. In this simulation, the spectrometer has a resolution of 1 nm and a SNR of 50.  
proposed method is fully compatible with the scientific requirements stated in Section 2. Figure 8 illustrates the results obtained with such a configuration. The retrieval of concentrations for the other gases also remains excellent with this instrumental configuration. Parsing out specific details from this intricate dataset, such as the concentration of a particular greenhouse gas, is challenging. Inversion methods offer mathematical techniques to dissect this convoluted signal, but the intricacies of the atmospheric interactions and the sheer complexity of the data make these methods intricate and demanding. Additional research could be undertaken to explore the inversion outcomes when clouds and aerosols are present, as they have the potential to introduce biases in the determination of GHG concentrations (CO\({}_{2}\) and CH\({}_{4}\)) observed via the Uvsq-Sat NG NIR Spectrometer. The Uvsq-Sat NG measurements can also be affected by airglow, which is a light emitted by oxygen molecules in the high atmosphere. The oxygen airglow spectrum at 1.27 \(\upmu\)m closely resembles the O\({}_{2}\) absorption spectrum, which is used to estimate the sunlight atmospheric path and serves as a proxy for airmass. For instance, in the case of the MicroCarb mission, two wavelength bands are used for CO\({}_{2}\) concentration measurement normalization: the O\({}_{2}\) A band (0.76 \(\upmu\)m) and the absorption band at 1.27 \(\upmu\)m. The O\({}_{2}\) A band (0.76 \(\upmu\)m) is used to derive the O\({}_{2}\) column, which contributes in understanding the atmospheric path length and scattering effects [32]. This information is crucial for accurately estimating the concentration of CO\({}_{2}\), given that the CO\({}_{2}\) absorption band occurs at a distinct wavelength (1.6 \(\upmu\)m). The spectral distance between the O\({}_{2}\) A band and the CO\({}_{2}\) absorption band introduces uncertainties due to varying aerosol properties and atmospheric scattering effects. However, using the O\({}_{2}\) absorption band at 1.27 \(\upmu\)m, which is closer to the CO\({}_{2}\) band, can help to mitigate some of these uncertainties. In the context of MicroCarb, the instrument's spectral resolution clearly enables the differentiation of airglow absorption, which disturbs the measurement of O\({}_{2}\) by filling the absorption lines. However, this capability is not achievable with Uvsq-Sat NG due to the insufficient spectral  
Figure 8: Restitution of the concentration of gases observed via the Uvsq-Sat NG NIR Spectrometer. In this simulation, the instrument has a resolution of 6 nm and a SNR of 2000.  
resolution of its spectrometer (1 to 6 nm in the wavelength range of 1200 to 2000 nm). This correction for the Uvsq-Sat NG NIR Spectrometer needs to be carried out using the Reactive Processes Ruling the Ozone Budget in the Stratosphere (REPROBUS) 3D chemistry transport model [33].