Climate change and globalisation are the dominant drivers of societal impacts in the Arctic with economic development rapidly transforming the geo-politics and the physical and biogeochemical environment of the region. For example, new prospectors are increasing their activities using modern techniques for oil and gas, fisheries and mineral resources, and commercial ship traffic is growing dramatically. Several areas of extreme concern have been recently raised by the International Panel for Climate Change: “There is high confidence that the probability of a sea-ice-free Arctic Ocean during summer is substantially lower at global warming of 1.5°C when compared to 2°C. With 1.5°C of global warming, one sea ice-free Arctic summer is projected per century. This likelihood is increased to at least one per decade with 2°C global warming. Effects of a temperature overshoot are reversible for Arctic sea ice cover on decadal time scales.” Permafrost thaw, extreme weather events, flooding, diminishing sea and land ice, and coastal erosion lead to unreliable ice roads, damage to houses, pipelines, railways, airports, ports and harbours, and impacts on energy and water supplies. Thus, the societal impacts of a rapidly changing Arctic are complex, uncertain and ambiguous. As an increasing number of national and international stakeholders place more demands on the Arctic region, tensions and insecurity across the region as a whole are evident. In this evolving complex setting Arctic indigenous peoples remain extremely vulnerable.

In response, the European Commission and the High Representative of the Union for Foreign Affairs and Security Policy issued to the European Parliament and the Council, on 27 April 2016, a joint communication that proposed "An integrated European Union policy for the Arctic". Continuously monitoring the vast and harsh Arctic environment in a changing world is considered essential to the successful implementation and effective management of the Arctic Policy. The existing Copernicus programme already offers operational thematic services to monitor the atmosphere, marine environment, land, climate change, emergency management and security. However, new high-priority requirements from key Arctic user communities have emerged that highlight the need for new satellite measurements that are not currently available as part of the Copernicus satellite fleet.

Against this background, and starting from user needs articulated and prioritised by the European Commission Polar Expert Group (PEG), a Copernicus Imaging Microwave Radiometer (CIMR) candidate mission is under study by the European Space Agency. In the next years there is a potential gap in operational provision of low-frequency (6-10 GHz) satellite microwave radiometry that has been the foundation of operational sea surface temperature for CMEMS. Furthermore, operational continuity of sea surface salinity and thin sea ice thickness measurements pioneered by the L-band satellite microwave radiometers flown by the SMOS/SMAP research missions is not guaranteed. CIMR will uniquely observe a wide range of floating sea ice parameters (concentration, drift, type, thickness), sea surface temperature over the Polar and global oceans at high spatial resolution (4-15 km) and sea surface salinity, thin sea ice thickness, snow products, and surface wind speed at ~40 km. Additional measurement of other parameters (e.g. soil moisture, precipitation) will also be possible. All these products will have a high geophysical accuracy and temporal resolution. Through these measurements, CIMR will address the needs of Copernicus and provide evidence to underpin the management and monitor the impact of the Integrated European Policy for the Arctic.

The CIMR mission will deploy a wide-swath (>1900 km) conically scanning multi-frequency microwave radiometer. CIMR measurements will be made using a forward scan arc followed ~260 seconds later by a second measurement of the same location using a backward scan arc. Polarised (H and V) channels centred at 1.414, 6.925, 10.65, 18.7 and 36.5 GHz are included in the mission design under study. The real-aperture resolution of the 6.925/10.65 GHz channels is <15 km, 5 and 4 km for the 18.7/36.5 GHz channels respectively. The 1.414 GHz channel will have a real-aperture resolution of ~60 km (fundamentally limited by the size of the ~8m deployable mesh reflector). However, most channels will be oversampled allowing gridded products to be generated at much better spatial resolution. Channel NEdT is 0.2-0.8 K with an absolute radiometric accuracy goal of ~0.5K. CIMR will fly in a dawn-dusk orbit providing, with one satellite, ~95% global coverage every day (except for rain conditions), better than daily coverage poleward of 55°N and S, and no gap in coverage at the pole itself. CIMR will operate in synergy with the EUMETSAT MetOp-SG(B) mission so that in the polar regions (>65N and 65S) collocated and contemporaneous measurements between CIMR and MetOp MWI/ICI and SCA measurements will be available within +/-10 minutes.

This presentation provides an overview of scientific basis and proposed technical implementation of the candidate CIMR mission.

The “CSC Expansion” programme includes 6 new missions that have been identified by the European Commission (EC) as priorities for implementation in the coming years by providing additional capabilities in support of current and emerging user needs.

The L-band SAR mission represents one of these 6 missions. L-band SAR satellite missions and their imagery data have proven capabilities to fulfil a large variety of operational applications, which are currently not covered in Copernicus. Thus the primary objectives of the L-Band SAR mission are linked to the major observational gaps in current Copernicus space component and to current and future needs of operational services which include emerging cross-cutting applications not covered by the current services but strongly connected to Copernicus application domains.

The mission target applications are: soil moisture, crop type discrimination, forest type/forest cover/forest change (in support to biomass estimation), food security and precision farming. In addition, the mission will contribute in strong way to the monitoring of polar ice sheets and ice caps, sea ice extent in the polar region, and of seasonal snow. Other emerging applications will be possible by the synergetic and complementary observations with C-band and X-band SAR systems, creating a Radar Observing System for Europe (ROSE).

The requirements for L-Band SAR mission cannot be considered in isolation but need to build on existing and planned Copernicus observation capabilities and infrastructure to derive maximum benefits for users and services. Observational gaps filled by the L-Band SAR mission requires careful combination of the new information with information provided by existing Sentinel missions. The enhanced continuity also requires harmonised, coordinated and systematic acquisitions in conjunction with other Sentinel data, and in particular those provided by the C-band radar aboard Sentinel-1. This has two reasons:
• the unique information provided by L-Band SAR is due to the high penetration capability of the L band radar. Besides penetration through cloud that characterize radar in comparison to optical imaging, the long L-Band SAR wavelength is capable to penetrate through many other natural media, such as vegetation, dry snow, ice. This enables L-Band SAR to provide additional information that cannot be gathered at higher frequency, such as that of Sentinel-1. As such, L-Band SAR and Sentinel-1 will complement each other to constitute a quasi multi-frequency (multi-band) space-born SAR system capability on an operational basis that is currently only provided by individual specific airborne SAR campaigns. Examples of this include extending current surface motion products to areas covered with vegetation or providing enhanced sea ice mapping capabilities. From the user point of view elements such as coverage, time latency between the acquisitions and availability of the data all needs to be harmonised to ensure maximum benefits.
• the L-Band SAR mission provides additional European radar imaging capacity above and beyond that provided by Sentinel-1 and thus an opportunity to increase coverage at European and Global level, reducing the time intervals between successive radar images. For services such as the Copernicus Emergency Management Service (EMS) reducing time between the occurrence of a natural or anthropogenic disaster and the first post-disaster image is of crucial importance. In general, user requirements generally point to a daily revisit capability at European and Global level (see Sentinel-1 MRD) which is an achievable goal when considering Sentinel-1 and L-Band SAR as a combined system.

These above features of the L-Band SAR mission - together with the operational and service orientation of the mission design (e.g. reliability, data timeliness, European free and open data policy, systematic acquisitions etc…) - distinguish this mission from other non-European L-band SAR mission initiatives and provide unique opportunities to support the evolution of the Copernicus Programme.

Evolution in the Copernicus Space Component (CSC) is foreseen in the mid-2020s to meet priority Copernicus user needs not addressed by the existing infrastructure, and/or to reinforce services by monitoring capability in the thematic domains of CO2, polar, and agriculture/forestry. This evolution will be synergetic with the enhanced continuity of services for the next generation of CSC.
The “High Spatio-Temporal Resolution Land Surface Temperature Monitoring (LSTM) Mission”, identified as one of the CSC Expansion High Priority Candidate Missions (HPCM), currently undergoes an ESA preparatory phase (phase A/B1) study to establish mission feasibility.
The LSTM mission shall provide enhanced measurements of land surface temperature with a focus responding to user requirements related to agricultural monitoring.
Earth surface thermal variations occur at various time and space scales in relation to both natural and human-induced processes. These variations are connected to the surface energy and water balance and their interaction with the surface-atmosphere boundary layer. Thermal observations are therefore critical to address a range of applications and scientific objectives, and closely complement observations of other environmental variables. Those applications include products for agriculture and associated water resources management, precision farming and crop yield forecasting. Earth observation (EO) monitoring products based on thermal observations are therefore considered important for policy making including amongst others the UN Sustainable Development Goals (e.g. SDG 6.4), the UN Convention for Combating Desertification and Land Degradation, the UN Water Strategy, the EU Common Agriculture Policy, the EU Policy Framework on Food Security, the EU Water Framework Directive and the EU 2030 agenda for Sustainable Development.
Specifically, monitoring of high resolution thermal signatures allows e.g. assessment of crop water status and overall water stress, support to irrigation management and optimisation of scarce water resources for crop production, and further allows to derive essential soil parameters that cannot be retrieved in the VNIR/SWIR spectral range. This would support the implementation of resilient agricultural practices, maintaining ecosystems and progressively improving land, soil and water quality, and thus leading to sustainable agriculture. In this context, high-resolution thermal images, as a basis for evapotranspiration retrieval, will directly reveal water conservation practices or the need thereof. Unauthorised water abstractions can be detected by comparing evapotranspiration maps with volumetric water rights.
Surface temperature derived from thermal infrared (TIR) observations is already being obtained from spaceborne TIR sensors e.g. MODIS, Sentinel-3 and Landsat however, at spatio-temporal resolutions insufficient for many applications and services including agriculture at European field scales making the case for future TIR satellite missions addressing global water and food security issues (Fisher et al., 2017).

MISSION OBJECTIVES

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.
The existing Copernicus space infrastructure, in particular Sentinel-1 and Sentinel-2, already provides useful information for agricultural applications. Although Sentinel-3 already provides global LST measurements, the limited 1km spatial resolution does not capture the field-scale variability required for irrigation, crop growth modelling and reporting on crop water productivity. In view of the foreseen evolution in Copernicus, additional high-level observation requirements have been assessed and discussed at the EC Copernicus Agriculture and Forestry User Requirement Workshop in 2016, revealing the lack of European spaceborne capability for providing high spatio-temporal resolution Thermal Infrared (TIR) observations . Therefore, a dedicated LSTM mission is foreseen in the frame of the Copernicus evolution with the overall objective:

To complement Sentinel observation capabilities with high spatio-temporal resolution Thermal Infrared observations over land and coastal regions in support of agriculture management services, and possibly a range of additional services.

The LSTM mission would deploy one or more satellites equipped with TIR instruments optimised to support agriculture management services with the specific mission objectives below. Based on the European and international policies the mission objectives are specified as:

• Primary objective: to support monitoring evapotranspiration (ET) rate at European field scale by capturing the variability of Land Surface Temperature (LST) (and hence ET) enabling more robust estimates of field-scale water productivity.
• Secondary objective: to support mapping and monitoring the soil composition (mineralogy and organic matter) and its dynamics through emissivity estimates.
• Complementary objective: to support a range of additional services benefitting from TIR observations (e.g. coastal zone management, High-Temperature Events (HTE), urban heat islands).

The primary objective requires observations of LST and emissivity (essential for derivation of LST) while the secondary objective can be satisfied with just the estimates of emissivity (Bastiaanssen and Harshadeep, 2005; Bastiaanssen et al., 2008; Sobrino et al. 2016). The additional services that could be included in the complementary objective in most cases also require observations of both LST and emissivity.

HIGH-LEVEL MISSION REQUIREMENTS

In response to the priority user needs, the initial Mission Requirements Document (MRD) for the space component has been developed by an international Mission Expert Group (MEG) under European Space Agency (ESA) leadership. The MRD serves as a starting point for the preparatory phase study, by conveying the EU policy framework, the user needs, the objectives and the observation requirements for each candidate mission. The objective of the LSTM MEG was to advise ESA on the definition of requirements for a future operational space component to meet user needs in the context of a Copernicus mission contributing to Agriculture Monitoring and potentially additional domains.
At the beginning of 2018 an ESA Mission Advisory Group (MAG) was selected and established as part of an open call. The MAG will follow and provide advice to ESA throughout the Phase A/B1 preparatory phase activities, and in particular for the consolidation of mission requirements.

FEASIBILITY STUDY PHASE

Upon identification of the LSTM mission as a high priority candidate, and with the MRD prepared by the MEG, a number of ESA Phase A/B1 preparatory activities have been planned. Based on a competitive ESA industrial tender, two parallel competitive system level studies have now been kicked off with European industrial consortia, each of which will be conducted over the course of 2018 and early 2019. The objective of the system level activities and accompanying support studies and campaigns is to establish the feasibility of each of the two respective mission concepts, with the goal to arrive at a consolidated mission design by mid-2019. At the end of 2019 a decision on the content of the Copernicus Expansion and selected missions is anticipated amongst ESA member states at a Council meeting at Ministerial level.

CONCLUSIONS

Based on user requirements collected by the European Commission the “High Spatio-Temporal Resolution Land Surface Temperature Monitoring (LSTM) Mission” has been identified as one of the CSC Expansion High Priority Candidate Missions (HPCM). Over the course of the next year, the prospective LSTM Sentinel mission will be studied in further detail, which started in spring 2018. The mission requirements consolidation is expected to be an on-going process, supported by the MAG, industrial and scientific studies and campaign activities in 2018-19. A consolidated Copernicus Expansion plan and decision on which HPCM candidates proceed to full implementation is expected at the end of 2019. The CSC is co-funded by the EU and ESA with complementary roles. Proper funding through programme subscriptions by ESA Member States and by the EU within its next Multiannual Financial Framework is a requisite for a successful implementation of the CSC evolution scenario including CSC expansion missions

1. Introduction
Evolution in the Copernicus Space Component (CSC) is foreseen in the mid-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 CO2, polar, and agriculture/forestry. This evolution will be synergetic with the enhanced continuity of services for the next generation of the Copernicus Space Component.
Growing expectations about the use of Earth observation data to support policy making and monitoring puts increasing pressure on technology to deliver proven and reliable information. Hyperspectral imaging (also known as imaging spectroscopy) today enables the observation and monitoring of surface measurements (geo-biophysical and geo-biochemical variables) due to the diagnostic capability of spectroscopy provided through contiguous, gapless spectral sampling from the visible to the shortwave infrared portion of the electromagnetic spectrum.
Hyperspectral imaging is a powerful remote sensing technology based on high spectral resolution measurements of light interacting with matter, thus allowing the characterization and quantification of Earth surface materials. Quantitative variables derived from the observed spectra, e.g. directly through distinct absorption features are diagnostic for a range of new and improved Copernicus services with a focus on the management of natural resources. These services support the monitoring, implementation and improvement of a range of related policies and decisions.
Thanks to well-established spectroscopic techniques, optical hyperspectral remote sensing has the potential to deliver significant enhancement in quantitative value-added products. This will support the generation of a wide variety of new products and services in the domain of agriculture, food security, raw materials, soils, biodiversity, environmental degradation and hazards, inland and coastal waters, and forestry. These are relevant to various EU policies, that are currently not being met or can be really improved, but also to the private downstream sector.
The Main Mission Objective of the Copernicus Hyperspectral Imaging Mission is:
“To provide routine hyperspectral observations through the Copernicus Programme in support of EU- and related policies for the management of natural resources, assets and benefits. This unique visible-to-shortwave infra-red spectroscopy based observational capability will in particular support new and enhanced services for food security, agriculture and raw materials. This includes sustainable agricultural and biodiversity management, soil properties characterization, sustainable mining practices and environment preservation.”

1. Mission requirements
The observational requirements of CHIME are driven by the primary objectives i.e. agriculture, soils, food security and raw materials, and are based on experience, state-of-the art technology and results of previous hyperspectral airborne and experimental spaceborne systems. They were drafted by an international group of experts in reflected in the Mission Requirement Document. These baseline observational requirements consider trade-offs and dependencies between parameters such as spectral resolution and radiometric performance. These high-level requirements are distinguishable in:
• Spatial coverage and geometry
• Observation Time
• Timeliness
• Revisit Time
• Spatial Requirements
• Spectral Requirements
• Radiometric Requirements
• Calibration Requirements
Currently the main mission objectives require a contiguous spectral coverage between 400 and 2500 nm, a spectral sampling interval about 10 nm, a spatial sampling interval in the range of 20 – 30 meters and a geometric revisit time of 10 to 15 days at an equator nodal crossing time between 10:30-11:30.

2. CHIME Phase A/B1 activity
Based on the analysis of observation requirements and identification of preliminary system concepts two parallel CHIME Phase A/B1 contracts were kicked off in early 2018.

As a result of CHIME Phase A, parametric analyses identifying the critical parameters and defining a set of performance requirements corresponding to the optimum in cost vs. benefits for a number of proposed mission concepts were provided. As part of the contract a variety of concepts covering a range of mission implementations going from a lower to higher implementation complexity are currently being evaluated. High-level preliminary implementations which could be foreseen include concepts based either on a single instrument module design, or a combination of modules on a single satellite or a small constellation of identical satellites. In the last case, a deployment strategy will also be proposed.

With the technological advances of large FOV optics and large format 2D detector arrays, an imaging spectrometer concept based on pushbroom acquisition is a good candidate to fulfil most of the observation requirements. These types of instruments have been implemented by ESA in the past with CHRIS on the PROBA-1 as technology demonstrator (in 2001), MERIS on-board ENVISAT (in 2002) and OLCI on-board Sentinel-3 (in 2016). All those instruments are imaging grating spectrometers acquiring spectrally resolved images of the Earth surface in the VIS/NIR spectral range.
Compared to CHRIS/MERIS/OLCI imaging spectrometers, an increase of the spectral range and the Ground Sampling Distance (GSD) is necessary to comply with CHIME observation requirements.

3. Technology Developments
The combination of large FOV optics and wide spectral coverage together with increased spatial resolution require the development of large and fast 2D detector arrays and wide range spectral separation systems (e.g., grating, prism).
Further high data rates (> 1 Gbit/s) resulting from increased Field of View (FOV) and low Ground Sampling Distance (GSD) request to assess suitable on-board data compressions/cloud screening/processing combined with an improved data transmission strategy.

4 Data Products, Usage and Access
As far as end user products are concerned, considering that many of the applications exploiting hyperspectral data rely on surface reflectance spectra, Level-2A products (atmospheric and geometrically corrected surface reflectance) are requested as the main data product to be distributed to users by the mission core ground segment.
The main features of the Level-2A product are:
- Bottom-of-Atmosphere (BOA) reflectance pixel-level information.
- Ortho-rectified geometry including the usage of a Digital Elevation Model (DEM);
- Appended pixel classification (side product from the atmospheric correction process) allowing to distinguish opaque clouds, thin clouds, cloud shadows, vegetation, etc.
Additionally, access to Level-1B and Level-1C products are required to give the possibility to advanced users to perform their own atmospheric correction.
Level-1B products are Top-of-Atmosphere (TOA) radiance products. The Level 1b product consists of quality controlled L1a data that have been reformatted but not resampled in segments. Pixel quantity expressed as Top of Atmosphere (TOA) radiance (Wm-2sr-1 μm-1) with all the radiometric and spectral calibration applied. Geometric information (e.g. refined viewing model) computed and appended, but not applied. Preliminary pixel classification (e.g. land/water/cloud/sun-glint mask) and landmarks are included in the product.
Level-1C products are Top-of-Atmosphere (TOA) reflectance products in ortho-rectified geometry (same cartographic projection as Level-2A products). The Top Of Atmosphere reflectance are resampled in cartographic reference frame UTM/WGS84 and framed tiles. Level 1c products are geometrically refined including geolocation correction from any residual bias and thermo-elastic distortion (intra-orbit and seasonal) and multi-temporal registration.
Complementing the core products above, a set of downstream products can be proposed to users as part of the mission catalogue or as service offer from the EO value adding industry.

5 Synergies and International Context
In terms of potential for synergies with other missions and especially with Sentinel-2, a hyperspectral mission would be complementary to Sentinel-2 for many fields of application, and in particular for vegetation-related and land cover mapping applications for which Sentinel-2 is optimized. Synergies with Sentinel-2 could help slightly relax the requirements for high temporal resolution in the case of e.g. agriculture and in-land water applications, and the spatial sharpening of hyperspectral images with Sentinel-2 data could also help some of the applications requiring a high spatial resolution.
On the other side, there are planned hyperspectral missions aiming for moderate spatial resolution (~ 30 m) multi- to hyperspectral image data.
The recent Decadal Survey prioritised the hyperspectral Surface Biology Geology (SBG) mission as “designated” missions to perform observations considered essential to the overall NASA programme.
Further, the Environmental Mapping and Analysis Program (EnMAP) for an imaging spectrometer mission with 30m spatial resolution and 30km swath is in Phase D production for a 2020 launch by the DLR with a five-year mission.
The PRISMA (PRecursore IperSpettrale della Missione Applicativa) is a hyperspectral Italian Space Agency program with 30 m pixels, 30 km swath with a 5-year life and a planned 2019 launch.
The Japanese Hyperspectral Imager Suite (HISUI) will be deployed in a non sun synchronous orbit aboard the International Space Station in the 2019 time-frame, following the VNIR ‘DLR Earth Sensing Imaging Spectrometer’ (DESIS), which was deployed onto the ISS in June 2018.

All those complementary missions provide excellent opportunities for evaluating synergies with CHIME observation requirements. They will help to define the best-suited mission within the CHIME Phase A/B1 study.