## 1 Introduction  
Global warming results from anthropogenic GreenHouse Gases (GHGs) emissions, which disrupt the delicate balance between incoming solar radiation and the Earth's reflected shortwave and emitted longwave (thermal) radiation. Understanding these energy exchanges within the Earth-atmosphere system is therefore essential. One of the earliest relatively comprehensive assessments of these exchanges was presented by [PERSON] and [PERSON] (1997) [1], as illustrated in Figure 1. This energy budget was later thoroughly revised by [PERSON] et al. (2012) [2]. The Earth's climate is fundamentally governed by radiative energy fluxes at the Top-Of-Atmosphere (TOA) boundary. The Earth's Radiation Budget (ERB) quantifies both the incoming and outgoing radiative energy at the TOA and comprises three principal components: the Incoming Solar Radiation (ISR), also known as Total Solar Irradiance (TSI); the Reflected Solar Radiation (RSR), also referred to as Outgoing Shortwave Radiation (OSR); and the Outgoing Longwave Radiation (OLR), which represents thermal energy emitted by the Earth. Due to their critical importance for understanding and predicting climate change, these ERB components are classified as Essential Climate Variables (ECVs), whose continuous monitoring is mandated by the Global Climate Observing System (GCOS) under the coordination of the World Meteorological Organization (WMO). Among these parameters, the Earth's Energy Imbalance (EEI) is particularly significant, as it provides a direct measure of the net radiative forcing driving climate change [3,4]. Defined as the residual between incoming and outgoing energy fluxes--EEI = ISR - OSR - OLR--this imbalance reflects the energy state of the Earth system and serves as a critical metric for assessing the current status and progression of global climate change. One of the latest Earth heat inventories [5] reveals that the Earth system has persistently accumulated heat, with an estimated total of 381 \(\pm\) 61 ZettaJoules (ZJ) added between 1971 and 2020. This corresponds to a heating rate, or EEI, of 0.48 \(\pm\) 0.1 Wm\({}^{-2}\). The vast majority of this accumulated heat--approximately 89%--is stored in the oceans, followed by about 6% on land, 1% in the atmosphere, and roughly 4% contributing to the melting of the cryosphere. Figure 1: Earth’s annual global mean energy budget based on the Kiehl and Trenberth study (1997) [1]. The Earth's radiation budget can be monitored using two complementary approaches: in situ ocean measurements and space-based satellite observations. In situ measurements, such as those from the Argo network [6], provide highly accurate estimates of EEI over long timescales but are limited in capturing short-term variations due to sampling constraints. Alternatively, satellite instruments offer continuous and global coverage of the ERB by measuring both incoming solar radiation and outgoing Earth radiation with higher temporal resolution and stability. Together, these methods provide a comprehensive picture of the Earth's radiative energy exchanges. Among these, satellite measurements play a crucial role in monitoring the ERB, particularly at the TOA boundary, where incoming solar and outgoing terrestrial radiation are most directly observed. To date, seven Clouds and the Earth's Radiant Energy System (CERES) instruments have been launched aboard five satellites--the Tropical Rainfall Measuring Mission (TRMM), Terra, Aqua, Suomi National Polar-orbiting Partnership (S-NPP), and NOAA-20--providing essential diurnal and angular sampling of the Earth's radiative fluxes. To capture the full diurnal cycle, the seven CERES instruments have operated over time from two complementary satellite orbital configurations, one with a Local Time of Descending Node (LTDN) around 10:00 a.m. and another with a Local Time of Ascending Node (LTAN) near 2:00 p.m., with some missions still ongoing and others now completed.