# UVsq-Sat NG, a New CubeSat Pathfinder for Monitoring Earth Outgoing Energy and Greenhouse Gases
## 2 Scientific Objectives
### Carbon Dioxide and Methane  
Table 1 also presents GHGs' scientific requirements related to Uvsq-Sat NG and the Terra-F hypothetical French satellite constellation. Keep in mind that Terra-F is currently a conceptual mission and has not yet entered its development phase. However, achieving this level of precision with such a constellation would accomplish several key objectives regarding mapping the global distribution of CO\({}_{2}\) and CH\({}_{4}\) concentrations with high spatio-temporal resolution. This would allow us to monitor the variability and co-evolution in CO\({}_{2}\) and CH\({}_{4}\) concentrations over different regions on a wide range of temporal scales (e.g., from diurnal to seasonal timescales) and to constrain the quantification of their sources and sinks. This would contribute to a better understanding of the carbon cycle and its role in climate change. The main challenge in understanding CH\({}_{4}\) source and sink processes lies in the absence of accurate global measurements of atmospheric CH\({}_{4}\). Existing ground-based in situ observations are limited due to the coarse measurement network, making it difficult to adequately sample key source regions like the Arctic permafrost, boreal forests, and tropical wetlands. Space-borne measurements are essential in order to achieve comprehensive global coverage with high precision.  
Various space missions have been dedicated to the measurement and continuous monitoring of GHGs in the Earth's atmosphere. One can mention the Environmental Satellite (ENVISAT) and its Scanning Imaging Absorption Spectrometer for Atmospheric Chattorography (SCIAMACHY) [16; 17], Greenhouse Gases-Observing Satellite (GOSAT) [18; 19] and its Thermal and Near-Infrared Sensor for Carbon Observation Fourier Transform Spectrometer (TANSO-FTS), TanSat (also known as CarbonSat), or even Orbiting Carbon Observatory-2 (OCO-2) [20] and OCO-3. Most of these satellites are equipped with sophisticated spectrometers that can precisely measure the GHG concentrations in the Earth's atmosphere. For example, OCO-2 uses an NIR/shortwave infrared grating spectrometer with multiple bands (0.76 \(\upmu\)m for O\({}_{2}\), 1.61 \(\upmu\)m and 2.06 \(\upmu\)m for CO\({}_{2}\)). Its spatial resolutions are 1.29 km (cross-track) and 2.25 km (along-track), making it suitable for precise GHG monitoring. It is the second successful high-precision CO\({}_{2}\)-observing satellite (better than 0.3%), after GOSAT. Other satellites currently under development aim to improve these measurements and to precisely quantify atmospheric gas emissions, a wide range of spatial scales, from the global to specific point sources [21]. Examples of such space missions are MicroCarb (2024), GOSAT-3 (2024), MethaneSAT (2024), GeoCarb (2025), CO2M (2025), or even Merlin (2028). As an illustration, the MicroCarb mission [22] is designed to measure CO\({}_{2}\) columns using a high-spectral-resolution infrared grating spectrometer (with a resolving power of \(\sim\)25,000). This spectrometer operates in lines specific to CO\({}_{2}\) (at 1.6 and 2.0 \(\upmu\)m) and O\({}_{2}\) (at0.76 and 1.27 \(\upmu\)m), providing a spatial resolution of 250 \(\times\) 400 km. A recent study [23] also explored the potential of observing GHGs from CubeSats [24]. Such SmallSats, especially in constellation, could play an important role in GHG remote sensing, despite their compact and mass limitations. One of the Uvsq-Sat NG mission's objectives is to assess the feasibility of measuring the atmospheric GHG (CO\({}_{2}\), CH\({}_{4}\)) columns using a miniaturized spectrometer aboard a CubeSat. On the top of ERB measurements, Uvsq-Sat NG aims to develop and validate an in-orbit demonstrator of GHG observations at lower spectral resolutions. The satellite's successful implementation will pave the way for future high-resolution satellite constellations. State-of-the-art codes and procedures will have to be carried out in order to assess the quality and precision of the satellite measurements, ensuring their adherence to scientific standards.