## 1 Introduction
Thanks to multiple CERES instruments aboard different satellites operating at varying local times, a robust understanding of Earth's radiation budget has been established. While significant progress has been made in sampling the diurnal cycle, improving the absolute accuracy of EEI measurements remains a key challenge--alongside the need for broader coverage across a wider range of local observation times. To address these issues, innovative approaches have been explored. [PERSON] et al. (2017) [7] demonstrated that a notional Earth Observation Radiometer constellation using Wide Field-Of-View (WFOV) broadband radiometers can retrieve both spatial and temporal information with high fidelity. However, despite the improved sampling such constellations offer, [PERSON] et al. (2018) [8] argued that ensuring precise calibration and inter-calibration among WFOV radiometers remains a major obstacle--drawing on lessons from instruments like those flown on the Earth Radiation Budget Experiment (ERBE) [9]. In particular, [PERSON] et al. (2018) [8] identified several sources of uncertainty in non-scanner radiometers, including on-orbit gain and offset variations due to thermal effects, radiometric degradation (especially in the shortwave), uncertainties from flux inversion for anisotropic radiance fields, inter-satellite calibration inconsistencies due to footprint mismatches, and biases introduced by changes in satellite altitude. These limitations, inherent to WFOV non-scanner instruments and the complexity of radiative flux retrieval, highlight the persistent challenge of achieving the radiometric precision necessary for climate monitoring. Consequently, several methods have been proposed to determine the EEI, but none have yet achieved the required accuracy [4]. Nevertheless, recent advances in instrument technology and the growing availability of small satellite platforms have renewed interest in employing broadband non-scanning WFOV instruments for EEI measurements. As part of our effort to monitor the ERB, we have developed and deployed a series of small satellite demonstrators in orbit since 2021. This initiative led to the design and implementation of a heterogeneous constellation of satellites with WFOV instruments, representing the first European program specifically dedicated to such measurements. Uvsq-Sat, the inaugural mission [10], was launched on 24 January 2021 into a Sun-Synchronous Orbit (SSO) with an LTDN of approximately 9:30 a.m., and remained operational until its atmospheric reentry on 30 October 2024. The second mission, Inspire-Sat [11], was launched on 15 April 2023, with an LTAN of 10:30 a.m. and re-entered the atmosphere on 18 September 2024. Most recently, the third satellite, Uvsq-Sat NG [12; 13; 14], was launched on 15 March 2025 into a similar orbit, with an LTAN close to 10:25 a.m. at an altitude of 600 km. This new mission is expected to ensure the continuity of the measurement series initiated by the previous satellites, strengthening our long-term commitment to ERB monitoring. This manuscript focuses on observations made by the Uvsq-Sat and Inspire-Sat satellites between February 2021 and October 2024, as well as those from CERES between 2013 and the end of 2024. In Section 2, we emphasize the importance of measuring both the Earth's radiation budget and the Earth's energy imbalance. Section 3 briefly introduces the Uvsq-Sat and Inspire-Sat CubeSats, their Earth Radiative Sensors (ERS), calibration methods, and how they address key challenges in ERB observations. Section 4 presents the methodology used to process data from the Uvsq-Sat and Inspire-Sat missions based on orbital time-series. In Section 5, we present new ERB observations at TOA from the Uvsq-Sat mission, covering the period from February 2021 to October 2024. We analyze global trends and variability in TOA radiation and compare our findings with those from the CERES dataset.