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Evolution in the Copernicus Space Component (CSC) is foreseen in the second half of 2020s to meet priority user needs not addressed by the existing infrastructure, and/or to reinforce services by monitoring capability in the thematic domains of CO 2 , polar, and agriculture/forestry. This evolution will be synergetic with the enhanced continuity of services for the next generation of CSC.

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.

Sentinel-3 is a Global Land and Ocean monitoring mission developed in the frame of the joint EC/ESA Copernicus initiative. Carrying a suite of cutting-edge instruments, Sentinel-3 will measure systematically Earth’s oceans, land, ice and atmosphere to monitor and understand large-scale global dynamics. It will provide essential information in near-real time for ocean and weather forecasting. Four identical Sentinel-3 satellites are planned that will collectively provide a 20-year period of continuous observations. The Sentinel-3A (S3A) satellite was launched on the 16th of February 2016. Sentinel-3B satellite is under development and will be launched in 2017. Sentinel-3C and D satellites are in preparation as replacement for the A and B units. In this paper we will describe the S3A optical payload and summarize the first commissioning phase results.

The Sentinel-3A satellite, the first of a series of four satellites from the European Commission’s Copernicus Programme, was launched on the 16th of February 2016. Sentinel-3 is a multi-instrument mission to measure sea-surface topography, sea- and land-surface temperature, ocean colour and land colour to support ocean forecasting systems, as well as environmental and climate monitoring. The presentation will focus on Sentinel-3 optical instruments, namely the Ocean Land Colour Imager (OLCI) and the Sea and Land Surface Temperature Radiometer (SLSTR). The results of the five-month commissioning phase (concluded in July 2016) are presented. The Level-1 product quality is presented as well as preliminary verification and validation results of the Level-2 ocean products.

SLSTR is a high accuracy infrared radiometer which will be embarked in the Earth low-orbit Sentinel 3 operational GMES mission. SLSTR is an improved version of the previous AATSR and ATSR-1/2 instruments which have flown respectively on Envisat and ERS-1/2 ESA missions. SLSTR will provide data continuity with respect to these previous missions but with a substantial improvement due to its higher swaths (750 km in dual view and 1400 km in single view) which should permit global coverage of SST and LST measurements (at 1 km of spatial resolution in IR channels) with daily revisit time, useful for climatological and meteorological applications. Two more SWIR channels and a higher spatial resolution in the VIS/SWIR channels (0.5 km) are also implemented for a better clouds/aerosols screening. Two further additional channels for global scale fire monitoring are present at the same time as the other nominal channels.

The product generation from hyperspectral sensor data has high requirements on the processing infrastructure, both hardware and software. The Airborne Prism Experiment (APEX) processing and archiving facility has been set up to provide for the automated generation of level-1 calibrated data and user-configurable on-demand product generation for higher processing levels. The system offers full reproducibility of user orders and processing parameters by employing a relational database. The flexible workflow software allows for the quick integration of novel algorithms or the definition of new processing sequences. Reprocessing of data is supported by the archiving approach. Configuration management based on the database enables the control over different versions of processing modules to be applied. The system is described with a focus on the APEX instrument; however, its generic design allows adaptation to other sensor systems.

The airborne ESA-APEX (Airborne Prism Experiment) hyperspectral mission simulator is described with its distinct specifications to provide high quality remote sensing data. The concept of an automatic calibration, performed in the Calibration Home Base (CHB) by using the Control Test Master (CTM), the In-Flight Calibration facility (IFC), quality flagging (QF) and specific processing in a dedicated Processing and Archiving Facility (PAF), and vicarious calibration experiments are presented. A preview on major applications and the corresponding development efforts to provide scientific data products up to level 2/3 to the user is presented for limnology, vegetation, aerosols, general classification routines and rapid mapping tasks. BRDF (Bidirectional Reflectance Distribution Function) issues are discussed and the spectral database SPECCHIO (Spectral Input/Output) introduced. The optical performance as well as the dedicated software utilities make APEX a state-of-the-art hyperspectral sensor, capable of (a) satisfying the needs of several research communities and (b) helping the understanding of the Earth’s complex mechanisms.

For the validation of snow/ice products of the Advanced Earth Observing Satellite-II/Global Imager (ADEOS-II/GLI), several field campaigns were performed for various types of snow conditions with the Moderate Resolution Imaging Spectroradiometer (MODIS) and GLI overpasses at four sites in Alaska and eastern Hokkaido, Japan from 2001 to 2005. The target satellite-derived snow parameters are snow surface temperature, mass fraction of soot, and two types of snow grain size retrieved from different spectral channels. The retrieved satellite products were compared with in-situ measured snow parameters based on snow pit work and snow sampling. The satellite-derived snow surface temperatures agreed well with in-situ measured values with a correlation coefficient ( R c ) of 0.900 and a root-mean-square error (RMSE) of 1.1 K. The satellite-derived mass fractions of soot were close to in-situ measured mass fractions of snow impurities for the snow layer between the surface and down to 7 or 10 cm rather than between 0 and 2 cm, while the satellite-derived absolute values were lower than the in-situ measured ones ( R c = 0.506 and RMSE = 5.0 parts per million by weight (ppmw)). This discrepancy is due primarily to the difference in the composition of snow impurities assumed in the satellite algorithm (soot) and measured in-situ (mineral dust) suggesting that the satellite retrieval of soot is not producing soot concentrations in many cases but rather dust. Snow grain sizes retrieved from two satellite channels at λ = 0.460 and 0.865 μm had better accuracy ( R c = 0.840 and RMSE = 125 μm) than those from a satellite channel at λ = 1.64 μm ( R c = 0.524 and RMSE = 123 μm) from the comparison with simply depth-averaged snow grain size. When similar comparisons are made with the depth-averaged measured grain size by a 1 / e weighting using flux transmittance, the results for R c and RMSE are not improved due to some difficulties in calculating the depth-averaging by a 1 / e weighting. For all our satellite products, the possible causes of errors are (1) satellite sensor calibration and (2) the bidirectional reflectance model (directional emissivity model for surface temperature) used in the algorithm together with the atmospheric correction. Two ways to improve the in-situ measurements are (1) the representativeness of the measured values and (2) the measuring methods. Field measurements also indicated that the increased reflectance due to “sun crust” observed at wet snow surfaces under clear sky could cause an underestimation of satellite-derived snow grain size. This problem will be more severe for the grain size retrieved from the channel at λ = 1.64 μm.

Efficient and accurate imaging spectroscopy data processing asks for perfectly consistent (i.e., ideally uniform) data in both the spectral and spatial dimensions. However, real pushbroom-type imaging spectrometers are affected by various point spread function (PSF) nonuniformity artifacts. First, individual pixels or lines may be missing in the raw data due to bad pixels originating from the detector, readout errors, or even electronic failures. Second, so-called smile and keystone optical aberrations are inherent to imaging spectrometers. Appropriate resampling strategies are required for the preprocessing of such data if emphasis is put on spatial PSF uniformity. So far, nearest neighbor interpolations have been often recommended and used for resampling. This paper shall analyze the radiometric effects if linear interpolation is used to optimize the spatial PSF uniformity. For modeling interpolation effects, an extensive library of measured surface reflectance spectra as well as real imaging spectroscopy data over various land cover types are used. The real measurements are systematically replaced by interpolated values, and the deviation between original and resampled spectra is taken as a quality measure. The effects of nearest neighbor resampling and linear interpolation methods are compared. It is found that linear interpolation methods lead to average radiometric errors below 2% for the correction of spatial PSF nonuniformity in the subpixel domain, whereas the replacement of missing pixels leads to average errors in the range of 10%-20%

Recently, the Advanced Earth Observing Satellite 2 (ADEOS-2) was launched (December 14, 2002) successfully, and the Global Imager (GLI) onboard the ADEOS-2 satellite became operational in April 2003. In a first calibration checkup, the radiometric performance of GLI was compared relatively to that of other sensors on different satellites with different calibration backgrounds. As a calibration site, a large snowfield near Barrow, Alaska, was used, where space sensors in polar orbits view the same ground target on the same day with small differences in the local crossing times. This is why GLI, the Moderate Resolution Imaging Spectroradiometer (Terra, Aqua), the Sea-viewing Wide Field-of-view Sensor, the Advanced Very High Resolution Radiometer (N16, N17), the Medium Resolution Imaging Spectrometer, and the Advanced Along Track Scanning Radiometer datasets were selected for the following clear-sky condition days: April 14 and 26, 2003. At the same time, ground-truth experiments (e.g., measurements of ground reflectance, bidirectional reflectance distribution function, aerosol optical thickness) were carried out. Thereinafter, top-of-atmosphere (TOA) radiance/reflectance was forward calculated by means of radiative transfer code for each sensor, each band, and each day. Finally, the vicariously retrieved TOA signal was compared to TOA sensor Level 1B data. As a result, GLI's performance is encouraging at that time of the mission. GLI and the other seven sensors deliver similar sensor output in the range of about 5% to 7% around the expected vicariously calculated TOA signal.

The SLSTRs are high accuracy radiometers selected for the GMES mission Sentinel-3 space component to provide SST data continuity respect to previous (A)ATSRs for climatology. Many satellites, each with 7.5-year lifetime, over a 20- year period are foreseen. Sentinel-3A will be launched in 2014 and Sentinel-3B at least 6 months later implying that two identical satellites will be maintained in the same orbit with 180° phase delay. Each SLSTR has an improved design respect to AATSR affording large near nadir and oblique view swaths (1400 and 740 km) for SST/LST global coverage at 1 km spatial resolution with a daily revisit time (with two satellites), appropriate for climate and meteorology. Clouds screening and other products are obtained with 0.5 Km spatial resolution in visible and SWIR bands while two additional channels are included to monitor high temperature events, such as forest fires. The two swaths are obtained with two conical scans and telescopes combined optically at a common focus, representing the input of a cooled Focal Plane Assembly, where nine channels are separated with dichroic and focalized on detectors with appropriate optical relays. IR and SWIR optics/detectors are cooled to 85 K by an active mechanical cryo-cooler with vibration compensation, while the VIS ones are maintained at a stable temperature. The opto-mechanical design and the expected electro-optical performance of the Focal Plane Assembly are described and the models predictions at system level are compared with experimental data acquired in the vacuum chamber in flight representative thermal conditions or in laboratory.

The Ocean and Land Colour Imager (OLCI) is a high accuracy visible spectral imager selected as optical payload for the Sentinel 3 component of the GMES mission, to provide climatological data continuity with the previous ESA Envisat missions. OLCI is based on the very successful opto-mechanical and imaging design of MERIS. The instrument is a quasi-autonomous, self contained, visible-NIR push-broom imaging spectrometer and incorporates significant improvements when compared to MERIS. The paper highlights the technical and programmatic challenges of the project, first results from the EM test activities and a projected flight model performance summary.

Since 1991, along track scanning radiometers (A)ATSR have been flown on a series of satellite platforms. These instruments use an along-track scanning design that provides two views of the same earth target through different atmospheric paths. Dual-view multispectral measurements can be used to derive an accurate atmospheric correction when retrieving geophysical parameters such as Sea Surface Temperature (SST). In addition, the (A)ATSR family of instruments use actively cooled detector systems and two precision calibration blackbody targets to maintain and manage on-board calibration. Visible channel calibration is implemented using a solar diffuser viewed once per orbit. As a consequence of these design features, resulting data derived from (A)ATSR instruments is both accurate and well characterized. After 10 years of Service the ENVISAT platform was lost in early 2012 asnd AATSR operations stopped. The Global Monitoring for Environment and Security (GMES) Sentinel-3 “Sea Land Surface Temperature Radiometer“ (SLSTR) instrument is the successor to the AATSR family of instruments and is expected to launch in April 2014. The challenge for SLSTR is to develop and deliver a new instrument with identical or improved performance to that of the (A)ATSR family. The SLSTR design builds on the heritage features of the (A)ATSR with important extensions to address GMES requirements. SLSTR maintains the main instrument principles (along-track scanning, a two point infrared on-board radiometric calibration, actively cooled detectors, solar diffuser). The design also includes more spectral channels including additional bands at 1.3 and 2.2 μm providing enhanced cloud detection, dedicated fire channels, an increase of dual view swath from 500 to 740 km, an increase in the nadir swath of 1400 km. The increase in swath has led to, a new optical front-end design incorporating two rotating scan mirrors (with encoders to provide pointing knowledge) and an innovative flip mechanism to select a specific optical chain. Unavoidably, these improvements introduce complexity, risk, increased mass and power. Bearing these aspects in mind, this paper reviews the design and performance of the Sentinel-3 SLSTR.

The European Union-ESA Global Monitoring for Environment and Security (GMES) programme decided to develop the Sentinels as first series of operational satellites in order to meet specific Earth observation user needs. The series of Sentinel-3 satellites will provide global, frequent and near-realtime ocean, ice and land monitoring. It continues Envisat's altimetry, the multispectral, medium-resolution visible and infrared ocean and land-surface observations of ERS, Envisat and Spot, and includes enhancements to meet the operational revisit requirements and to facilitate new products and evolution of services. The first launch is expected in 2013. In this paper an outline of the Sentinel-3 satellite and optical payload is presented. Dedicated calibration and validation activities regarding the sea and land surface temperature radiometer (SLSTR) and ocean and land colour radiometer (OLCI) are then reviewed. Calibration and validation (calval) activities are based on the heritage gained from ENVISAT MERIS and AATSR experience and cover pre-launch, in-orbit commissioning and operational measures for the Sentinel 3 satellites.