EE12 MISSION ADVISORY GROUPS

CryoRad

Earth’s cold regions drive important processes that control global water, heat, energy, and chemistry budgets. The continuing rapid changes in these regions are therefore affecting human activities at all latitudes through processes that remain incompletely understood. Substantial uncertainties remain in the magnitude of cryospheric feedback mechanisms and tele-connections, impairing climate predictability. While weather and climate prediction models have improved significantly over the last decade, uncertainties in cryospheric processes consistently point to the need for more accurate estimates of key geophysical parameters. Indeed, substantial gaps exist between the needs of model and users and current observational capabilities for multiple key parameters. Observations from space are essential for more accurate description of the processes that dominate polar regions, but existing or planned space-borne sensors do neither provide all the necessary geophysical parameters nor at the required spatial coverage and resolution, or with a sufficient revisit time, or an acceptable uncertainty.

The CryoRad mission will address critical observational gaps through an innovative ultra-wideband low-frequency microwave radiometer (frequency range 0.4-2 GHz) that is able to provide innovative products, i.e. microwave brightness temperatures in a frequency range that has never been exploited synergistically before. In particular, these CryoRad measurements will allow the estimation of:

• • • temperature profiles within ice sheets and ice shelves from the top to the bottom, that are only available from a few scattered boreholes;
    • sea-surface salinity in cold water with unprecedented accuracy to improve our knowledge of freshwater fluxes and ocean circulation;
    • sea-ice thickness in the range 0-1 m with improved accuracy with respect to current capabilities, and sea-ice salinity for the first time from space.

CryoRad is therefore unique in its ability to observe multiple key parameters of the cryosphere and polar ocean, thereby addressing multiple scientific questions, quantifying responses to climate changes for different surface types, and expanding understanding of the interactions among these processes. CryoRad’s overarching science objective is therefore to provide a better understanding of polar processes from the ice sheet interior to the open ocean.

Earth Climate Observatory (ECO)

The Earth climate system, the environmental and the societal consequences of the climate change are most fundamentally controlled by the Earth Energy Imbalance (EEI). The EEI is the difference between the solar radiation entering the Earth and the radiation outgoing from the Earth. The EEI has so far essentially been inferred indirectly from sea-level and global temperature rise, because no systems offered the capability to measure and monitoring it directly. The uncertainties inherent to the necessary modelling with this approach exceed the stringent climate requirements set for accuracy and stability of global mean EEI. Morevover, the global temperature rise and more generally the Earth system has a time delayed response of one or two decades to past EEI. Hence, insufficient observations of current EEI prevent revealing the trajectory of the future climate warming in the next decades with the accuracy required for immediate climate actions.

The Earth Climate Observatory, or ECO, mission has been established to support the societal need to constrain future global warming. ECO aims at directly measuring the difference between the solar radiation entering and the radiation outgoing from the Earth system in global annual mean with unprecedented coverage, accuracy and stability in line with GCOS requirements. The EEI has been increasing rapidly in recent decades, nearly doubling, and the underlying reasons for this surge remain incompletely understood. Therefore, accurate and stable monitoring of EEI is essential:

• • • to better predict climate evolution and for societies to adapt to global warming;
    • to monitor the effects of the decreasing emissions of greenhouse gases as set in the Paris agreement;
    • to progress on our current scientific understanding of how the overall Earth climate system works.

ECO would achieve accurate and stable measurement of EEI with a baseline constellation of 2 (or more) identical satellites, each carrying two Wide Field of View (WFOV) radiometers which measure directly at the satellite level both the fluxes in the UV to far infrared outgoing from the Earth and incoming from the Sun. The baseline configuration enables to sample the diurnal and seasonal cycles whilst providing global coverage. The ECO calibration strategy includes occasional turning of the satellites upside down to measure the incoming solar irradiance with the Earth-pointing radiometer, and vice-versa.

The ECO mission concept is unique in that it would allow to measure the EEI directly for the first time, using a satellite constellation. In the baseline, the 2 satellites orbit would precess in order to capture sub-daily and seasonal cycles and to secure an accurate global annual mean EEI. Unlike previous missions, EEI from ECO would hence not rely on substantial modelling of diurnal cycle, annual cycles, angular distributions, nor would it rely on observations of ocean heat content or sea level estimates over many years, or complex instrument cross-calibration, which are source of significant biases and uncertainties. This mission would lead to unprecedented accurate and stable EEI observations on a short time scale (annual) which constitute a breakthrough with respect to current EEI estimates. An aspirational third satellite is considered in a sun-synchronous orbit, hence travelling across the 2-satellite baseline, to further strengthen the EEI coverage and the intercalibration of the constellation.

Auxiliary multi spectral cameras complete the ECO mission concept. They aim at providing high spatial resolution spectral imaging within the visible, near-infrared and thermal wavelength ranges for climate model evaluation, cloud and aerosol process studies, and for synergies with other missions. These cameras are calibrated to match the onboard WFOV radiometers, allowing mapping and cross-calibration with international Earth radiation missions, such as CERES and the follow-on Libera. Their measurements will also greatly enhance synergies with European missions, such as FORUM, TRUTHS and IASI-NG, and enhance the operational international meteorological imagers that provide the high space/time resolution ISCCP-NG imagery and products.

The accuracy and stability of ECO’s EEI are strongly needed for mitigating and adapting to climate change as well as for better understanding how the climate system works. ECO addresses this important goal thanks to a unique and smart mission concept which bypasses critical retrieval steps present in other previous EEI estimates, and which lead to large bias. Therefore, the independent view on EEI offered by ECO is unique, scientifically exciting and societally urgently needed.

EEI observations provided by ECO would close an essential science gap in European EO capabilities. Moreover, the ECO design is a test bed that, if successful, could pave the way for new standards in EEI satellite measurements and to its operational monitoring.

Hydroterra+

As climate change effects become more severe, it is vital to study how water systems, i.e. hydrology, and the Earth’s physical structure, i.e. geology, are interconnected. Managing water efficiently is essential for agriculture, urban development, and environmental conservation, and it relies on advanced monitoring and forecasting technologies. At the same time, accurately predicting intense storm events, like Mesoscale Convective Systems, requires timely and precise data. This is crucial for improving weather predictions and disaster readiness, and it ties into the importance of understanding the cryosphere’s contribution to the global water and energy cycles. This knowledge is not just important for managing water resources and reducing flood risks; it also helps us comprehend the cryosphere’s impact on water availability and its influence on weather patterns. Moreover, the observation of ground movements caused by earthquakes, volcanoes, and landslides, often influenced by water saturation, highlights the need for these combined studies. This integrated approach enables more accurate assessments of natural hazards and the development of effective mitigation strategies, illustrating the complex interplay between storm dynamics, surface water, cryospheric changes, and the Earth’s geophysical stability within the larger framework of climate resilience.

To address these aspects, Hydroterra+ (H+), aims to:

• • • enhance the understanding of intense storm dynamics and their contribution to regional rainfall patterns by providing atmospheric water vapour and surface soil moisture maps;
    • advance knowledge on the diurnal land surface water budget, encompassing aspects such as soil moisture and vegetation hydration;
    • provide detailed insights into the cryospheric water budget, focusing on snow accumulation and melt cycles;
    • improve the detection and monitoring of ground motion events, including earthquakes, volcanoes, and landslides by providing vertical deformation and change maps.

H+ is based on a single payload, a C-band Synthetic Aperture Radar (SAR), in geostationary orbit to observe rapid processes (i.e. hours to days) of the water cycle over Europe, the Mediterranean basin, and parts of Africa. Nine footprints of 210000 km² each are constantly monitored twice a day at a spatial resolution of approx. 60 x 60 m², covering about 40% of continental Europe. H+ also encompasses the possibility of monitoring a specific area, e.g. for emergency scenarios, with a single footprint scanned 9 times every 55 minutes. The consolidated C-band SAR technology alongside the innovative placement in the geostationary orbit give H+ many benefits, including sensitivity to water vapour, soil moisture and deformation; a near-instantaneous access to one-third of the Earth, enabling continuous imaging capability and persistent link for data downlink and exploitation; and a unique complementarity with current Low-Earth Orbit (LEO) remote sensing missions.

Keystone

The upper atmospheric region spanning the altitude range from 70 to 120 km, the Mesosphere – Lower Thermosphere (MLT), is one of the least well-known regions of the planet. It is subject to high energy inputs from space, in the form of solar electromagnetic radiation and energetic particles (mostly electrons and protons of solar origin). The MLT is out of reach for in-situ measurements from balloons or aircraft, and too low for persistent satellite orbits due to residual drag, primarily due to atomic oxygen (O), the most abundant species at this height. O is produced by photodissociation of molecular oxygen (O₂ and O₃); it drives the (photo-) chemical processes and controls the cooling of the MLT by emission of infrared radiation by CO₂. However, despite its importance, O abundance and variability are poorly known. The reason for this is that existing infrared (IR) and visible ultraviolet (UV-Vis) remote sensing techniques only offer indirect determination of atomic oxygen in the MLT and there is no global and/or long-term dataset for O to date.

Keystone is an upper atmospheric limb sounding mission with the aim of providing a comprehensive measurement of the MLT composition, temperature and winds, and its variability (from a diurnal to a seasonal scale). The key science objective of the mission is to gain knowledge of geophysical parameters in this region that can allow a better understanding of its behaviour. The mission aims to improve the understanding of space weather and climate change processes, particularly their impact on the MLT. This translates in understanding the composition, gradients, and variability of the aforementioned parameters, such as atmospheric neutral density, temperature, winds, and trace gases.

To this end, Keystone pursues the following five mission objectives:

• • • Thermal balance: to quantify reaction rates in chemical and photochemical models of the upper atmosphere by providing global vertical distribution profiles of the key MLT species atomic oxygen (O), in combination with co-located measurements of infrared heat fluxes and visible ultraviolet (UV-Vis) airglow. This is addressed through measurements of: O, temperature, infrared (IR) heat loss, and airglow.
    • Diurnal variations of the whole atmosphere: to investigate the 4-D space-time structure of the diurnal variations (atmospheric tides) in view of dynamics, chemistry, and electromagnetic processes. This will be addressed through measurements of winds, temperature, O, ozone (O₃), and ozone related species (e.g., HO_x, H₂O).
    • Upward coupling: to unveil the vertical propagation of synoptic-to-planetary scale disturbances from the middle atmosphere (non-migrating tides and Sudden Stratospheric Warming (SSW) events) to the upper atmosphere. This is addressed through measurements of temperature, winds, ion density and gravity waves.
    • Downward coupling: to understand atmospheric variations due to energy inputs from the magnetosphere (particle precipitation and magnetic storms). This is addressed through measurements of NO_x, HO_x.
    • Models & applications: to provide benchmarks for the whole atmosphere models and climate models with detailed description of the background thermal structure and distribution of minor species. This is addressed through measurements of H₂O, O₃, CO (tracer).

The Keystone mission concept comprises a satellite in Low-Earth Orbit (LEO) with a payload including a set of spectrometers operating in the Terahertz (THz), IR and UV-Vis electromagnetic spectrum domain. The instruments scan the limb of the atmosphere at tangent heights from 50 km to 150 km with high vertical resolution. The LEO orbit has a low inclination and precessing local equator crossing times, to resolve diurnal variations in geophysical observables. Measuring the zonal and meridional mesospheric wind vector components requires two orthogonal measurements of the movement a given air parcel. Keystone proposes to measure the components of the velocity by exploiting the line-of-sight Doppler shift in the THz spectral lines, whilst staring 45° forward and then 45° backward across the orbit track (i.e., looking sideways).

Keystone would provide the first comprehensive global, multiyear observations of the MLT