## 1 Introduction  
Broadband top-of-atmosphere (TOA) Reflected Solar Flux (RSF) is an essential climate variable of which a high-quality data record of satellite measurements with sufficient length (\"Climate Data Record\" or CDR) is needed by, among others, the climate modeling and climate monitoring communities, preferably spanning several decades [1]. To this end, various approaches have been proposed and implemented (a review is available in [PERSON] and Clerbaux [2]). In the Earth Radiation Budget Experiment (ERBE) [3], narrow- and wide-Field-Of-View (FOV) radiometers have been deployed. In recent Earth Radiation Budget (ERB) missions, such as the Clouds and Earth's Radiant Energy System (CERES) [4], the Geostationary Earth Radiation Budget (GERB) [5] or the Scanner for Radiation Budget (ScaRaB) [6], the narrow-FOV approach has been selected because the wide-FOV provided limited scientific outcomes due to the enormous size of the FOV and the difficulty of relating the fluxes with particular scene types. All these dedicatedERB missions rely on broadband (BB) radiometers that provide integrated observations of the radiation over large parts of the electromagnetic spectrum: \"shortwave\" (0.3-4 \(\upmu\)m) and \"longwave\" (4-50 \(\upmu\)m). Such instruments are not widely deployed in space because the usefulness of their data is mostly limited to the particular ERB community. This is in contrast to other multi-spectral instruments, such as MODIS, which are useful for a wide range of different geophysical variables. In parallel to BB radiometers, several projects have provided useful ERB records that are not based on BB observations but on either atmospheric reanalysis, for example, ERA5 [7; 8], or on cloud observations complemented by radiative transfer models (RTMs). The latter is the case with the well known ISCCP-FH dataset [9] and with the recent TOA fluxes produced by the ESA Cloud_cci project [10; 11]. This approach has the advantage of simultaneously providing the all-sky and clear-sky TOA fluxes, allowing a direct estimation of the cloud radiative effect. Another advantage is that it can be applied to visible (and infrared) imagery of historical weather satellites that have been primarily designed for cloud observations (e.g., as in ISCCP). However, radiative transfer computations are more subject to biases due to the necessarily simplified description of optical properties of the surface, atmosphere, aerosols and cloudiness. As a third approach, TOA fluxes have been also estimated from visible (and infrared) observations from weather satellites using a so-called narrowband-to-broadband conversion, to estimate broadband radiation from one or several observations taken at different wavelengths in the spectrum. The conversion can itself be based on radiative transfer simulation (\"theoretical\" approach) or based on collocated observations with a broadband instrument (\"empirical\" approach). An example for longwave radiation is the widely used data record of HIRS OLR [12]. [PERSON] et al. [13] show how shortwave narrowband-to-broadband conversions have been used to derive a long dataset of TOA RSF using the visible channels of the Meteosat satellites (1983-2015); however, products based on geostationary satellites do not provide global coverage. Among those approaches and products, the global CERES products (first approach) are acknowledged to be the golden standard with respect to radiative flux data records, although two limitations can be identified: (1) the records are relatively recent, for example, starting in the year 2000 for the EBAF product; and (2) the products have a relatively coarse spatial resolution of 1\({}^{\circ}\) (lat-lon equal angle grid), cf. Figure 1a. To date, no harmonized global CDR of TOA RSF dating back to the 1970s or 1980s exists.