## 4 UVSQ-SAT First Observations
### UVSQ-SAT Maps Reconstruction  
UVSQ-SAT maps reconstruction (albedo and OLR) are based on UVSQ-SAT time series. Currently, the reconstruction of each map is based on a Gaussian function whose parameters are defined by the satellite altitude and its FOV. In addition, a method based on a deep learning (DL) algorithm has been developed to obtain the satellite attitude in order to better determine the Earth's albedo and OLR [18]. The satellite attitude can also be reconstructed from the measurements of an inertial measurement unit (IMU). UVSQ-SAT is equipped with a gyrometer to measure angular velocity, an accelerometer to measure gravity and linear acceleration, and a magnetometer to measure the Earth's magnetic field. The magnetometer allows to measure the direction and the intensity of the magnetic field. The objective is to gather these inertial and magnetic data in order to reconstruct the attitude of the satellite. Figure 13 shows the intensity of the Earth's magnetic field measured by UVSQ-SAT thanks to its different sensors. Regarding the albedo and OLR, preliminary results have been obtained by applying the methods described in this study and in [PERSON] et al. (2020) [1]. Figure 14 shows a reconstructed map of the Earth's albedo (February 2021) obtained from UVSQ-SAT instruments. The albedo due to the atmosphere comes from Rayleigh backscattering in the short wavelength range and from clouds, which contribute about two thirds of the total albedo. The effect of the TSI at the TOA is stronger in the tropics. The high albedo at polar latitudes due to the presence of snow and ice on the ground has an important effect. This is of interest to follow this evolution over time. There are also local differences due to the albedo of cloudy regions (intertropical zone of convergence) or the ground (Sahara). The albedo of the ground depends strongly on its nature, it can be very high for fresh snow (about 0.75) and low for vegetation (below 0.2). The albedo of the ocean remains very low and of the order of 0.1. It depends on the distribution of waves. Figure 13: Earth’s magnetic field intensity measured by UVSQ-SAT instruments. The calibrations are being validated to consolidate the absolute measurement bias. of small satellites. It will be necessary to combine simple instruments (wide FOV and wide wavelength band) with more complex instruments (narrow FOV and using on-board calibration sources to follow the evolution of the degradation of the instruments in orbit). The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) 3U CubeSat mission [19] develops a similar approach to demonstrate technologies for the measurement of Earth's radiation budget in order to implement a satellites constellation. [PERSON] et al. (2017) [17] showed how a constellation of satellites with broadband radiometers can provide both spatial and temporal information to accurately measure the ERB. [PERSON] and [PERSON] (2013) [20] proposed a constellation of space-based instruments, capable of overcoming sampling limitations and providing global and diurnal measurements of the Earth's outgoing radiation with accuracy. With advances in technology and miniaturization of instruments, it is possible to envision a constellation of small satellites capable of measuring outgoing and variable terrestrial radiation from the Earth. The \"UVSQ-SAT\" concept is fully integrated in this approach and shows a way. With a single low-orbiting satellite (UVSQ-SAT), it is possible to obtain \"satisfactory\" mappings of the OSR and the OLR at the TOA only every month (with a loss of short time-scale information). [PERSON] et al. (2020) [1] show that a constellation of at least 50 satellites is necessary to have at least a daily mapping. Indeed, a constellation of at least 50 satellites is a prerequisite to capture spatio-temporal variations (every three hours and ideally a resolution of a few km). This would be fundamental data to validate climate models. These data are used to validate models and the magnitude of energy imbalances at the TOA.