# UVSQ-SAT, a Pathfinder CubeSat Mission for Observing Essential Climate Variables
## 5 Final Discussion  
The analysis done in Section 4 highlighted the interest to implement a satellite constellation to measure the true Earth's energy imbalance, since only satellite observations of net radiation flux variability at TOA can provide information at shorter timescales.  
Figure 7 shows the daily Earth net radiation as a function of longitude for different terrestrial latitudes (real observations (o) and simulated (s) using a constellation of 15 satellites during a day of observations). With a constellation of 15 satellites (inclinations of \(30^{\circ}\), \(45^{\circ}\), \(60^{\circ}\), \(75^{\circ}\), and \(98.5^{\circ}\) and LTAN of 02:30, 10:30, and 18:30), one could have excellent EEI measurements during a day of observation. A constellation of 50 satellites would allow accurate measurements of the Earth's energy imbalance (errors less than \(\pm 1\,\mathrm{Wm}^{-2}\)) with the diurnal and multi-directional sampling, which are a prerequisite to capture spatio-temporal variations (e.g., every three hours and ideally a few km resolution).  
Figure 6: Spatial reconstruction of Earth’s net radiation binned into a \(1^{\circ}\)\(\times\)\(1^{\circ}\) latitude-longitude geographic grid that will be obtained with UVSQ-SAT. The source of data for the left upper panel was from CERES observations.  
Long term measurements are required using satellite constellations with recovery periods (inter-calibrations) for multi-decadal observations to track Earth's energy imbalance over time for predicting the future course of global warming and verifying that the measures taken for the climate are effective. Accurate annual net radiation figures from pole to pole are required and represent key scientific indicators. There is a net energy surplus at the Equator and a net energy deficit at the poles (see Figure 6, top left panel), so energy will flow from the Equator to poles. This energy is transferred poleward as latent and sensible heat (warm ocean water and warm, moist air move poleward, while cooler water and cooler, drier air move toward the Equator). The Equator-versus-pole energy imbalance is the fundamental driver of atmospheric and oceanic circulation. From UVSQ-SAT and its future constellation (Figure 8), we propose to monitor this parameter. In the case of a satellite constellation, the instrumental calibration (pre-flight calibration with the same primary standard source, in-flight calibration to monitor aging with the same process) aspects will have to be studied in detail to guarantee accuracy and precision for each satellite. Indeed, the determination of top of atmosphere global net radiation budget using broadband non-scanner instruments remains complex due to outstanding calibration challenges [46].  
Figure 8: From a very simple unitary CubeSat to an increasingly complex nanosatellite on which a small satellite constellation will be based.  
Figure 7: Daily Earth net radiation as a function of longitude for different terrestrial latitudes. (o) represents the real observations (CERES data). (s) represents the results obtained with a simulation of observations from a virtual constellation of 15 satellites (five different inclinations and three different LTAN).