The European Earth observation programme GMES (Global Monitoring for Environment and Security), now Copernicus (the European Earth Observation Programme) since December 2012, aims at providing environmental information to support policymakers, public authorities and both public and commercial users. A systematic monitoring and forecasting of the state of the Earth's subsystems is currently under development. Six thematic areas are developed: marine, land, atmosphere, emergency, security and climate change. A land monitoring service, a marine monitoring service and an atmosphere monitoring service will contribute directly to the monitoring of climate change and to the assessment of mitigation and adaptation policies. Additional GMES services will address respectively emergency response and security-related aspects. The pre-operational atmosphere service of GMES is currently provided through the FP7 projects MACC and MACC-II (Monitoring Atmospheric Composition and Climate). MACC combines state-of-the-art atmospheric modelling with Earth observation data to provide information services covering European Air Quality, Global Atmospheric Composition, Climate, and UV and Solar Energy. Within the radiation subproject (MACC-RAD) existing historical and daily updated databases for monitoring incoming surface solar irradiance are further developed. The service will meet the needs of European and national policy development and the requirements of (commercial) downstream services (e.g. planning, monitoring, efficiency improvements, integration into energy supply grids). The SOLEMI and the HelioClim 3 databases operated by respectively DLR and ARMINES and its subsidiary Transvalor have been specifically developed in several national, European and ESA projects to fulfil the requirements for long-term databases and NRT services. On its transition process from the precursor services HelioClim and SOLEMI the following User's Guide intends to summarize existing knowledge, which has been published only in a scattered manner. Part A 'Users' Expectations' describes the communities of users, their expectations and gives an overview of the compliance of the MACC RAD service with those. In Part B 'The legacy HelioClim 3 and SOLEMI databases', the current databases HelioClim 3 and SOLEMI as well as the methods used to convert satellite images into solar surface irradiance are presented. The quality of the retrieved irradiances is discussed. An overview of the operations and workflow is presented for the creation, updating and monitoring of these databases. Part C 'The new HelioClim 4 database' describes the new Heliosat 4 method and the new HelioClim 4 database and provides an overview of the operations and the workflow. Part D 'Quality control of estimates of irradiance' discusses the means to control the quality of the elaboration of the products and to assess the uncertainty of the estimates of irradiance. Part E 'Delivering products' is devoted to the supply of HelioClim 4 products. The products are defined. A prototype of a means to access the HelioClim 4 products is presented. It is intended to update this User's Guide regularly following the realisation of the MACC RAD service line.
