Earth’s atmosphere provides the background for the “sea of plasmas” surrounding Earth via its Ionosphere and the upper and middle Atmosphere, providing an interface layer through which a broad diversity of solar-terrestrial energy transfer processes takes place. Developing an integrative understanding of global geospace energy transfer processes affecting this layer is a major scientific challenge with important societal implications. The disciplines covering this interaction have a large, diverse and active international community, with significant expertise and heritage in the European Space Agency and Europe. Several ESA directorates have activities directly connected with this topic, and an ESA Heliophysics Working group has been appointed by several ESA Directors, under the direction of the ESA Director General, to work on optimizing synergies and to act as a focus for discussion, inside ESA, of the scientific interests of the Heliophysics community.Very recently, a Forum at the International Space Science Institute was set up, involving some of the above WG, to look towards developing a deeper understanding of the solar-terrestrial interactions between the Ionosphere and the upper- and middle atmosphere, thus possibly enabling the detection of signatures by natural and anthropogenic hazards.This presentation will provide a brief introduction to ongoing internal ESA cross discipline approaches, and then note some of the outcomes of this recent ISSI forum to set out a pathway to address this intriguing topic.

Une évolution de la Composante Spatiale de Copernicus (CSC) est prévue pendant la seconde moitié des années 2020 pour répondre aux besoins prioritaires des utilisateurs non couverts par l'infrastructure existante. La mission CHIME (Copernicus Hyperspectral Imaging Mission for the Environment) couvrira une partie de ces besoins en fournissant des mesures hyperspectrales pour des domaines applicatifs comme la sécurité alimentaire, l'agriculture et la gestion de matières premières. Cet article fournit une description de la mission CHIME et de son état de développement actuel.

Imaging spectroscopy has been identified by ESA, NASA and other international space agencies as key to addressing a number of most important scientific and environmental management objectives. To implement the critical EU- and related policies for the management of natural resources, assets and benefits, and to achieve the objectives outlined by NASA’s Decadal Survey in ecosystem science, hydrology and geology, high fidelity imaging spectroscopy data with global coverage and high spatial resolution are required. As such, ESA’s CHIME (Copernicus Hyperspectral Imaging Mission for the Environment) and NASA’s SBG (Surface Biology and Geology) satellite missions aim to provide imaging spectroscopy data at global coverage at regular intervals of time with high spatial resolution. However, the scientific and applied objectives motivate more spatial coverage and more rapid revisit than any one agency’s observing system can provide. With the development of SBG and CHIME, the mid-to-late 2020s will see more global coverage spectroscopic observing systems, whereby these challenging needs can be more fully met by a multi-mission and multi-Agency synergetic approach, rather than by any single observing system. Therefore, an ESA-NASA cooperation on imaging spectroscopy space missions was seen as a priority for collaboration, specifically given the complementarity of mission objectives and measurement targets of the SBG and CHIME. Such cooperation is now being formalized as part of the ESA-NASA Joint Program Planning Group activities. Among the others, calibration and validation activities (Cal/Val) are fundamental for imaging spectroscopy while the satellites are in-orbit and operating. They determine the quality and integrity of the data provided by the spectrometers and become even more crucial when data from different satellites, carrying different imaging sensors, are used by users worldwide in a complementary and synergetic manner, like it will be the case for CHIME and SBG data. Indeed, Cal/Val activities not only have enormous downstream impacts on the accuracy and reliability of the products, but also facilitate cross-calibration and interoperability among several imaging spectrometers, supporting their synergistic use. Accordingly, within the context of this cooperation, a Working Group (WG) on Calibration/Validation has been set up, aiming to establish a roadmap for future SBG-CHIME coordination activities and collaborative studies. This contribution aims to outline the key areas of cooperation between SBG and CHIME in terms of Calibration and Validation, and present the establishment of a roadmap between the two missions, focusing on the following topics: * Establishing an end-to-end cal/val strategy for seamless data products across missions, including transfer standards; * Measurement Networks and commonly recognised Cal/Val reference sites; * Status of atmospheric radiative transfer and atmospheric–correction procedures; * Standardisation and Quality Control of reference data sets; * Definition and implementation of joint airborne spectroscopy campaigns, such as the executed 2018 and planned 2021 campaigns, to simulate both missions and exercise the capabilities needed for eventual interoperability (incl. data collection, calibration, data product production); * Continuous validation throughout the lifetime of products; * Identifying other opportunities for efficiency and success through cooperation on calibration and validation, downlink capabilities and shared algorithms (e.g. compression and on-board data reduction).

In 2018 a joint ESA and NASA airborne campaign was orchestrated with the University of Zurich to advance cooperation and harmonization of algorithms and products from imaging spectrometer measurements. This effort was intended to benefit the future candidate European Copernicus Hyperspectral Imaging Mission for the Environment (CHIME) and NASA Surface Biology and Geology mission. For this campaign, the Airborne Visible/Infrared Imaging Spectrometer Next Generation was deployed from May to July 2018. Twenty-four study sites were measured across Germany, Italy, and Switzerland. All measurements were rapidly calibrated, atmospherically corrected, and made available to NASA and ESA investigators. An expanded 2021 campaign is now planned with goals to: 1) further test and evaluate new state-of-the-art science algorithms: atmospheric correction, etc; 2) grow international science collaboration in support of ESA CHIME and NASA SBG; 3) test/demonstrate calibration, validation, and uncertainty quantification approaches; 4) collect strategic cross-comparison under flights of space missions: DESIS, PRISMA, Sentinels, etc. In this paper, we present an overview of the key results from the 2018 campaign and plans for the 2021 campaign.

Evolution in the Copernicus Space Component is foreseen in the mid-2020s to meet priority user needs not addressed by the existing infrastructure, and/or to reinforce existing services. In this context, the European Commission is intending to evaluate the overall potential utility of a complementary Copernicus hyperspectral mission to be added to the Copernicus Sentinels fleet. Hyperspectral imaging is a powerful remote sensing technology that, allowing the characterization and quantification of Earth surface materials, has the potential to deliver significant enhancements in quantitative value-added products. This study aims to illustrate the interaction methodology that was set up to collect and assess user-driven requirements in different thematic areas to demonstrate the potential benefit of a future Copernicus hyperspectral mission. Therefore, an ad hoc interaction matrix was circulated among several user communities to gather preferences about hyperspectral-based products and services. The results show how the involvement of several user communities strengthens the identification of these user requirements. Moreover, the requirement evaluation is used to identify potential opportunities of hyperspectral imaging in addressing operational needs associated with policy obligations at European, national, and local levels. The frequency distribution of spectral range classes and spatial and temporal resolutions are also derived from the preference expressed by the user communities in each thematic area investigated.

The Copernicus EU program started in 1998 with the overarching aim to become Europe’s operational Earth Observation monitoring system providing data and information services. An essential part of the program is the Copernicus Space Component (CSC), which is managed by the European Space Agency (ESA) as responsible for the Copernicus Sentinels satellite constellations. The presentation will include an overview of the CSC Optical Imaging Family (OIF) currently operated missions, namely Sentinel-2 and Sentinel-3, and candidate potential missions being developed, namely Copernicus Hyperspectral Imaging Mission for Environment (CHIME) and High Spatio-Temporal Resolution Land Surface Temperature Monitoring Mission (LSTM). The next generation missions are not included here. Sentinel-2 is an Earth Observation mission developed by the European Space Agency (ESA) in the frame of the Copernicus program of the European Commission. The mission consists on a Multi-Spectral Instruments (MSI) on board a constellation of two satellites: Sentinel-2A launched in June 2015 and Sentinel-2B launched in March 2017. It covers the Earth’s land surfaces and coastal waters every five days under the same viewing conditions and every three days at mid-latitudes with high spatial resolution and a wide field of view. 5 day revisit (i.e. under same viewing conditions) is met at all latitudes of observations (not only at equator), and with the swath overlap and the S2 orbit repeat pattern (14+3/10 rev/day, i.e. a 3 day sub-cycle), 3 day geometric coverage is achieved at mid latitudes. Sentinel-3 mission is measuring sea surface topography, sea and land surface temperature, and ocean and land surface colour with high accuracy and reliability to support ocean forecasting systems, environmental monitoring and climate monitoring. The Sentinel-3 mission is jointly operated by ESA and EUMETSAT to deliver operational ocean and land observation services. CHIME, identified as one of the Copernicus Expansion High Priority Candidate Missions (HPCM), will provide routine observations through the Copernicus Programme for managing natural resources and assets in support of EU policy, and will complement currently flying multi-spectral missions such as Sentinel-2. Compared to multi-spectral missions, CHIME will have an increased number of narrow spectral bands (spectral resolution of 10nm with no gaps between bands) in the visible-to-shortwave infrared range (400-2500nm), which will allow for a more accurate determination of biochemical and biophysical variables. LSTM, also identified as one of the HPCM, will provide enhanced measurements of land surface temperature with a focus responding to user requirements related to agricultural monitoring. High spatio-temporal resolution thermal infrared observations are considered fundamental to sustainable management natural resources in the context of water and food security of a global society. Operational land surface temperature (LST) measurements and derived evapotranspiration (ET) are key variables in understanding and responding to climate variability, managing water resources for agricultural production, predicting droughts but also addressing land degradation, natural hazards, coastal and inland water management as well as urban heat island issues.

Imaging spectroscopy in the visible-to-shortwave infrared wavelength range (VSWIR), or nowadays more commonly known as ‘hyperspectral imaging’, for terrestrial Earth Observation remote sensing, dates back to the early 1980s when its development started with mainly airborne demonstrations. From its initial use as a research tool, imaging spectroscopy encompassing the VSWIR spectral range has gradually evolved towards operational and commercial applications. Today, it is one of the fastest growing research areas in remote sensing owing to its diagnostic power by means of discrete spectral bands that are contiguously sampled over the spectral range with which a target is observed. The main principles of imaging spectroscopy rely on the exploitation of light dispersion technologies to split the incoming light through a telescope before being projected onto detector arrays. The light dispersion can be achieved by using prism or diffractive grating optical systems, perpetually aiming for improved performances in terms of efficiency, straylight rejection, and polarization sensitivity. The sensor technique has been first used in airborne imaging spectroscopy since the early 1980s and later in spaceborne hyperspectral missions from the end of the 1990s onwards. Currently, several hyperspectral spaceborne systems are under development and in preparation to be launched within the next few years. Through hyperspectral remote sensing, physical, chemical, and biological components of the observed matter can be separated and resolved thus providing a spectral ‘fingerprint’. The analyses of the spectral absorptions often give rise to quantitative retrievals of components of the observed target. The derived information is vital for the generation of a wide variety of new quantitative products and services in the domain of agriculture, food security, raw materials, soils, biodiversity, environmental degradation and hazards, inland and coastal waters, snow hydrology and forestry. Many of these are relevant to various international policies and conventions. Originally developed as a powerful detection and analysis tool for applications predominantly related to planetary exploration and non-renewable resources, imaging spectroscopy now covers many disciplines in atmospheric, terrestrial vegetation, cryosphere, and marine research and application fields. There is an increasing number of visible/near-infrared (VNIR) imaging spectrometers emerging also as small payloads on small satellites and cubesats, built and launched by small-medium enterprises. These are targeted to address commercial applications mainly in agriculture, resources and environmental management, and hazard observations.

The world of Earth observation (EO) data is rapidly changing, driven by exponential advances in sensor and digital technologies. Recent decades have seen the development of extraordinary new ways of collecting, storing, manipulating, and transmitting data that are radically transforming the way we conduct and organize science. This convergence of technologies creates new challenges for EO scientists and data and software providers to fully exploit large amounts of multivariate data from diverse sources. At the same time, these technological trends also generate huge opportunities to better understand our planet and turn big data into new types of information services. This article briefly describes some of the elements of the European Space Agency's (ESA) EO Open Science program, which aims to enable the digital transformation of the EO community and make the most of the large, complex, and diverse data delivered by the new generation of EO missions, such as the Copernicus Sentinels.

Citizens are providing vast amounts of georeferenced data in the form of in situ data collections as well as interpretations and digitization of Earth-observation (EO) data sets. These new data streams have considerable potential for supporting the calibration and validation of current and future products derived from EO. We provide a general introduction to this growing area of interest and review existing crowdsourcing and citizen science (CS) initiatives of relevance to EO. We then draw upon our own experiences to provide case studies that highlight different types of data collection and citizen engagement and discuss the various barriers to adoption. Finally, we highlight opportunities for how citizens can become part of an integrated EO monitoring system in the framework of the European Union (EU) space program, including Copernicus and other monitoring initiatives.

The status of the European Space Agency Earth Explorer missions is presented. These science-driven missions have unique objectives and as of today, four out of the seven Earth Explorers missions have been launched, namely GOCE, SMOS, CryoSat, and Swarm. Three other Explorer missions: ADM-Aeolus, EarthCARE, and Biomass are in varying stages of development and are planned to be launched in the coming years. Furthermore, two candidate missions (FLEX and CarbonSat) are currently undergoing feasibility study prior to the competitive selection of the 8th Explorer mission late in 2015. Moreover, driving the selection of the next Earth Explorers, the new Earth Observation Science Strategy for ESA: A New Era for Scientific Advances and Societal Benefits, provides key elements and scientific direction for the future progress of ESA's Living Planet Programme is also described.

An overview is provided of the activities of the European Space Agency, ESA, to support the documentation, monitoring and management of Cultural Heritage through the use of Earth Observation, EO. These activities include: participation in international agreements; funding of service demonstration projects and support to researchers through the provision of data, training courses and the hosting of research students at the ESA European Space Research Institute, ESRIN, establishment. Since ESA and the United Nations Educational, Scientific and Cultural Organisation, UNESCO, signed the “Open Initiative on the Use of Space Technologies to Support the World Heritage Convention”, world heritage has become increasingly prominent in ESA as an emerging application area. Various demonstration projects have successfully revealed the potential to bridge the gap between research and operational service delivery. These projects include Heritage Observation and Retrieval Under Sand, HORUS, which used radar to document archaeological structures buried beneath the sand in Egypt, and ArchEO, a project recently kicked-off, aimed at demonstrating optical Earth observation techniques for the detection of archaeological structures in Poland. An increasing number of research projects are exploiting ESA and Third Party Mission, TPM, data for cultural heritage applications. Some of these include a project using radar remote sensing for subsurface archaeological feature detection, a project focussing on monitoring land subsidence over Syrian archaeological sites using Interferometric Synthetic Aperture Radar, InSAR, and a project documenting archaeological structures over the Silk Road in China. In addition to the provision of data and processing tools, ESA supports the heritage research and user community through training courses that focus on the application of EO for cultural heritage. Finally, ESA contributes to workshops to provide a forum for the heritage and remote sensing communities to exchange ideas, and provide insights into evolving user needs and technological achievements. ESA activities are driven by user requirements. The increasing involvement of ESA in EO related activities in cultural heritage is indicative of the emerging awareness of the benefits of EO on the part of the heritage community, and their growing interest in its integration into their activities. In order to most efficiently channel resources and plan future EO developments to meet this increased demand, interdisciplinary dialogue is essential between the heritage and remote sensing communities.

Imaging spectroscopy, also known as hyperspectral remote sensing, is based on the characterization of Earth surface materials and processes through spectrally-resolved measurements of the light interacting with matter. The potential of imaging spectroscopy for Earth remote sensing has been demonstrated since the 1980s. However, most of the developments and applications in imaging spectroscopy have largely relied on airborne spectrometers, as the amount and quality of space-based imaging spectroscopy data remain relatively low to date. The upcoming Environmental Mapping and Analysis Program (EnMAP) German imaging spectroscopy mission is intended to fill this gap. An overview of the main characteristics and current status of the mission is provided in this contribution. The core payload of EnMAP consists of a dual-spectrometer instrument measuring in the optical spectral range between 420 and 2450 nm with a spectral sampling distance varying between 5 and 12 nm and a reference signal-to-noise ratio of 400:1 in the visible and near-infrared and 180:1 in the shortwave-infrared parts of the spectrum. EnMAP images will cover a 30 km-wide area in the across-track direction with a ground sampling distance of 30 m. An across-track tilted observation capability will enable a target revisit time of up to four days at the Equator and better at high latitudes. EnMAP will contribute to the development and exploitation of spaceborne imaging spectroscopy applications by making high-quality data freely available to scientific users worldwide.

Water is our most precious and arguably most undervalued natural resource. It is essential for life on our planet, for food production and economic development. Moreover, water plays a fundamental role in shaping weather and climate. However, with the growing global population, the planet’s water resources are constantly under threat from overuse and pollution. In addition, the effects of a changing climate are thought to be leading to an increased frequency of extreme weather causing floods, landslides and drought. The need to understand and monitor our environment and its resources, including advancing our knowledge of the hydrological cycle, has never been more important and apparent. The best approach to do so on a global scale is from space. This paper provides an overview of the major components of the hydrological cycle, the status of their observations from space and related data products and models for hydrological variable retrievals. It also lists the current and planned satellite missions contributing to advancing our understanding of the hydrological cycle on a global scale. Further details of the hydrological cycle are substantiated in several of the other papers in this Special Issue.

The Managing Editor, Prof. Michael Rycroft, members of the Editorial Board and all members of staff at Springer who are connected with our journal are most grateful to the reviewers named below for their hard work and diligence when refereeing papers submitted for publication in 2012. Their assistance in raising the standard of the papers published in Surveys in Geophysics is immense, and is greatly appreciated.

The harmonization of operational data products and the creation of higher level information products such as global maps and time series (from different sensor sources) are required to satisfy the operational service requirements of the societal benefit areas as outlined in the GEOSS implementation plan. The CEOS working group on calibration and validation (WGCV) concentrates on defining standards and procedures aimed at allowing for the inter-comparison and ultimate utilization of data from all Earth observing platforms, both current and future. WGCV strives to establish common approaches to validation, calibration and data exchange formats to ensure effective cooperative use of all CEOS member space assets in addressing important global scale problems. This paper reviews the WGCV data assurance strategy, detailed system element requirements to guarantee data quality, and current WGCV activities for the generation and validation of products.

Many vegetation properties are related to features of reflectance spectra in the region 400 nm - 2500 nm. and to emittance in region 8 mm - 14 mm Detailed observations of spectral reflectance reveal subtle features related to biochemical components of leaves such as chlorophyll and water. Exchange of energy between the biosphere and the atmosphere is an important mechanism determining the response of vegetation to climate variability. This requires measurements of the component temperature of foliage and soil. The latter are closely related to the angular variation in thermal infrared emittance. The architecture of vegetation canopies determines complex changes of observed reflectance and emittance spectra with view and illumination angle. Quantitative analysis of reflectance and emittance spectra requires, therefore, an accurate characterization of the anisotropy of radiance. This can be achieved with nearly - simultaneous observations at different view angles. The Surface Processes and Ecosystem Changes Through Response Analysis (SPECTRA) Mission has been conceived to perform these observations at high spatial resolution by taking advantage of the spacecraft agility. Scientific preparations are pursued along two avenues: a) the nature of the expected data and candidate algorithms are evaluated by generating and using synthetic hyper - spectral multi - angular/radiometric data; b) algorithms are evaluated with actual hyper - spectral data collected with a variety of airborne systems and concurrent ground measurements; Campaigns have been performed using radiometric observations provided by ATSR, AATSR, AirMISR, CHRIS - PROBA and a variety of airborne hyperspectral systems. The paper will cover highlights of these studies.