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The three main objectives of the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) are to provide long-term high-quality climate records of vertical profiles of selected essential climate variables (ECVs), to constrain and calibrate data from more spatially comprehensive global networks, and to provide measurements for process studies that permit an in-depth understanding of the properties of the atmospheric column. In the five years since the first GRUAN implementation and coordination meeting and the printing of an article (Seidel et al.) in this publication, GRUAN has matured to become a functioning network that provides reference-quality observations to a community of users. This article describes the achievements within GRUAN over the past five years toward making reference-quality observations of upper-air ECVs. Milestones in the evolution of GRUAN are emphasized, including development of rigorous criteria for site certification and assessment, the formal certification of the first GRUAN sites, salient aspects of the GRUAN manual and guide to operations, public availability of GRUAN’s first data product, outcomes of a network expansion workshop, and key results of scientific studies designed to provide a sound scientific foundation for GRUAN operations. Two defining attributes of GRUAN are 1) that every measurement is accompanied by a traceable estimate of the measurement uncertainty and 2) that data quality and continuity are maximized because network changes are minimized and managed. This article summarizes how these imperatives are being achieved for existing and planned data products and provides an outlook for the future, including expected new data streams, network expansion, and critical needs for the ongoing success of GRUAN.

SA’s new Earth Observation Science Strategy aims to cover all areas of science to which Earth observation missions can contribute. It challenges ESA and the scientific community to advance knowledge and technology in order to respond to the increasing needs associated with risks and opportunities in our changing global environment. The strategy (SP-1329/1) provides key elements and scientific direction for the future progress of ESA’s Living Planet Programme. The context and specific scientific challenges to increase knowledge and capabilities in the five Earth science disciplines – atmosphere, cryosphere, land surface, ocean and solid Earth – are identified in the complementary volume (SP-1329/2).

ESA’s new Earth Observation Science Strategy aims to cover all areas of science to which Earth observation missions can contribute. It challenges ESA and the scientific community to advance knowledge and technology in order to respond to the increasing needs associated with risks and opportunities in our changing global environment. The strategy (SP-1329/1) provides key elements and scientific direction for the future progress of ESA’s Living Planet Programme. The context and specific scientific challenges to increase knowledge and capabilities in the five Earth science disciplines – atmosphere, cryosphere, land surface, ocean and solid Earth – are identified in the complementary volume (SP-1329/2).

Surface temperature data – observed primarily for weather-related purposes – are disparate, originating from ever evolving instrument types and observational practices. Although several global databases are in use internationally, no comprehensive global repository exists and many data are undigitized or restricted. Scientists have painstakingly obtained vast quantities of data, carefully removed random errors and accounted for systematic biases. The 21st Century demands go further - requiring highly detailed (spatially and temporally), globally complete, long-term products, with quantified uncertainties, and created from freely available, fully traceable data. Many decisions of substantial socio-economic importance rely on the accuracy of such products. An international meeting was held to plan how best to facilitate such efforts. A central repository is to be created, where data are traceable from their origins to final product. Strategies are outlined to rescue non-digitized data and move towards entirely freely available data. Creation of multiple methodologically independent products is recommended for quantifying uncertainty. Methods of benchmarking and assessing multiple products to aid inter-comparison and end-user product selection are described. Data-products would be obtained and visualized using in-house tools from the planned data-portal. Structure and governance include engagement with bodies such as WMO and, importantly, with experts other than climatologists.

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Over the past few years imaging spectrometer have increased in number and quality significantly. Directly correlated to this growth, is the need of (near-) simultaneous field work with non-imaging spectroradiometers. Due to severe constraints in technology requirements for these field instruments (portability, power supply, etc.), reliable portable instruments have become available later than their imaging correspondents. The systematic use of a large variety of ground instruments from their early stages in 1990 and onwards is therefore discussed and the need for reproducible radiometric measurements outlined. The assessment includes a review of calibration practices for non-imaging instruments and examples of sampling strategies needed for field data collection. Finally, a combined measurement facility (FIGOS/LAGOS) is presented, demonstrating the usefulness of measuring bi-conical reflectance factor under laboratory conditions (LAGOS, Laboratory Goniometer System), and its outdoor counterpart measuring hemispherical-conical reflectance (FIGOS, Field Goniometer System).