CryoSat-2 was launched twelve years ago, on the 8th April 2010. It was the first European mission dedicated to the cryosphere with the objectives to monitor precise changes in the thickness of polar ice sheets and floating sea ice. The satellite carries a radar altimeter called the Synthetic Aperture Interferometric Altimeter (SIRAL) which still remains one of the most innovative altimeters in space although newer versions are boarded on different satellites. It’s still the only mission that flies an interferometer. In future CRISTAL will have similar capabilities.

In its first twelve years in space, the CryoSat mission has systematically witnessed the changes that are affecting the ice fields of our planet due to global warming. CryoSat has been able to provide global sea-ice thickness and land ice mass balance, particularly over areas where the most dynamic changes are occurring

Beyond its originally scope, the mission supports wider scientific and operational applications in several domains. The mission has been recently extended until the end of 2025 with the scope to achieve new important goals, to extend the synergy with ICESat-2 and its unequalled data set and to secure a unique long-term climate record as long as possible. This will be possible thanks to well established international collaborations with many important worldwide institutions and agencies.
Scope of this paper is to describe the current mission status, show its main achievements and provide programmatic highlights for the extended period 2023-2025.

Launched in 2010, the European Space Agency’s (ESA) polar-orbiting CryoSat satellite was the first SAR/SARIn altimeter specifically designed to measure changes in the thickness of the sea ice and the elevation of the ice sheets and mountain glaciers. After 12 years in orbit, CryoSat continues to deliver high-quality data, providing unique contributions to several Earth Science and applications domains. Going beyond its ice-monitoring objective, CryoSat has also demonstrated to be a valuable source of observations for geodesic, hydrologic and oceanographic applications by measuring multi- thematic and high-resolution geophysical parameters. Being the only satellite flying an interferometric radar altimeter, CryoSat is also an important flying laboratory providing insights which are vital to prepare for future polar altimetry missions (e.g. Copernicus CRISTAL). To enable their full scientific and operational exploitation, the CryoSat products are routinely Quality-Controlled and thoroughly Validated (QCV) by ESA with the support of external scientific and technical teams. Based on the QCV results and feedback from the user community, the data products continuously evolve in order to accommodate a growing range of users and operational services over the sea ice, the land ice and the ocean domains. In this talk, we introduce the evolutions taken on board by the latest core baselines and give an overview of the quality assessment of the CryoSat data products, with an outlook to the new processing algorithm upgrades to be implemented in the ESA operational processing chains.

The ESA Earth Explorer CryoSat-2 was launched on 8 April 2010 and initially designed to contribute to the investigation of many debatable environmental issues related to global warming and its effect on the Cryosphere. Going beyond its ice monitoring objectives, CryoSat-2 has also demonstrated to provide a valuable source of observations over the ocean as well as for inland water level monitoring. Numerous CryoSat-based studies have been carried out by ESA since the beginning of the mission in order to optimize processing algorithms for these specific applications. A major step forward has consisted to build on these R&D outcomes and transpose them into an operational framework by generating new thematic products.

Beside “Core” Level-1 and Level-2 data evolution, the product portfolio has been recently enhanced, with the development of the Cryo-TEMPO (CryoSat’s ThEMatic PrOducts) concept which is now becoming a new standard for altimetry missions. These user-friendly and rapidly evolving products build on outcomes from the science literature and R&D projects mainly funded by the ESA Science for Society programme. The first pillar of Cryo-TEMPO was the development of the CryoSat EOLIS processor, from which swath thematic data are now produced operationally, both along track and gridded, for Antarctica and Greenland in addition to selected glaciers and ice caps. The second pillar consists of generating Sea Ice, Polar Sea, Land Ice, Hydrology and Coastal thematic data products, based on state-of-the-art processing methods, including CEOS-compliant uncertainty parameters which are necessary to assimilate data into forecasting systems and constrain reanalysis of climate models. More surprisingly, magnetic data measured by the three “platform magnetometers” on-board the CryoSat satellite have also become a systematic product (Cryo-MAGNET) which are now widely used by the Swarm science community for studying multi-scale variations of the Earth’s core magnetic field.

The purpose of this paper is to provide a general overview of the Cryo-TEMPO portfolio and related R&D projects which will aim at addressing new operational and science challenges for CryoSat while paving the way for the development of the CRISTAL Sentinel Expansion mission.

After more than 11 years of operational activity of the CryoSat satellite, the performance of the SIRAL instrument is in line or better than expected. The internal calibration measurements, designed to model a wide range of SIRAL’s imperfections, can be analyzed to highlight whether/how the instrument is changing over time and as function of its thermal status. Each variation of the instrument measured by the calibration data is compensated in the Level-1 processing. Inspection of the temporal evolution of the calibration data shows that SIRAL has been stable during its lifetime. The performance of SIRAL will be presented together with the results of the stability analysis on the calibration data, to verify that the instrument fulfills the requirements and that is maintaining the performance over its lifetime. To calibrate the SIRAL interferometer, an end-to-end calibration strategy using the ocean surface as the known external target, is exploited. The interferometer can be used to determine the across-track slope of the overflown surface and the slope of the ocean surface can be considered as known, starting from the geoid. In our analysis, the accuracy and the precision of the CryoSat interferometer will be presented starting from the residual errors on the measured angle of arrival obtained after compensation of the calibration function.

Simultaneous to the calibration activities, and in the framework of its FutureEO Programme the European Space Agency (ESA) regularly carries out ground-based and airborne campaigns to support geophysical algorithm development, calibration/validation, simulation of future spaceborne Earth observation missions, and applications development related to land, oceans and atmosphere. Under such framework, ESA has been conducting airborne and ground measurements campaigns in the polar regions since 2002 supporting all phases of the CryoSat mission. In particular, an overview of the validation campaigns, how these have evolved following the mission lifetime together with the latest results will be presented.

In August 2020 the CryoSat-2 satellite started a new mission chapter, raising its operational altitude by 887 meters. This change, however small compared to the total height (719 km), enabled an orbital resonance with NASA’s ICESat-2 spacecraft. As a consequence of this the instruments of these two satellites undergo recurring coincidences over the areas scientific interest every 1.3 days.

The main instrument of CryoSat 2 is the SAR/Interferometric Radar Altimeter (SIRAL), a single frequency Ku-band radar; whereas ICESat-2 is equipped with the Advanced Topographic Laser Altimeter System (ATLAS), which consists of six laser beams organized in three pairs: central, right, and left, as seen from the flight direction. The combined operation of these two instruments offer numerous opportunities of high scientific importance, especially because of their differences in snow penetration. Combined data of this kind has a scientific value which was already acknowledged in the past by the numerous airborne campaigns of NASA’s IceBridge mission. The current CryoSat - ICEsat configuration allows exploiting the benefits of this, while at the same time paving the way to future dual-frequency missions, such as CRISTAL.

Long coincidences occur every 19 CryoSat-2 orbital revolutions, with ICESat-2 completing 20 revolutions in the same time. But even under conditions of orbital resonance the overlap of both instruments cannot be maintained through a long geographical area. The reason for this is the large difference in orbital altitude, and therefore orbital period, between the two satellites. By tuning the target in orbit position for CryoSat 2, i.e. its orbital phase, the length of the coincidences can be maximized in the areas close to the polar regions. This leads to instrument overlap tracks that, in the best cases, can be of the order of 1000 km in length. Unfortunately, optimizing the conditions for one of the poles comes at the expense of reducing them for the opposite one.

The orbital change achieved in August 2020 was performed by means of a manoeuvre campaign with the following objectives: a) to raise the orbit up to the resonance altitude with ICESat-2; and b) to leave the spacecraft in an orbital phase such that coincidences with the ICESat-2 instrument are maximized in the Arctic. The operational concept, however, was already foreseeing potential re phasing campaigns in the future, which would optimize the conditions for the Antarctic region. The manoeuvre campaign lasted 16 days, in which a total of 14 manoeuvres were executed. This left enough time during the inter-manoeuvre periods to keep the SIRAL instrument in operation. For this purpose a mission planning orbit was created to support the transitory period between the former mission’s nominal orbit and the new one. After the orbital change CryoSat 2 has been operated in its new altitude and position, which yield periodic coincidences with the ICESat-2 instrument in the Northern hemisphere.

The CryoSat-2 mission foresees a major Antarctic campaign in November 2022. This presents an excellent opportunity to change the orbital phase, such that coincidences with the ICESat-2 instrument are switched over to the Southern hemisphere. This poster describes the details of the manoeuvre campaign necessary to achieve this, which is currently scheduled for the second quarter of 2022. The target phase is located approximately 6 degrees ahead of the current orbital position; this is equivalent to a node crossing time 100 seconds earlier than the current one. All other orbital parameters remain the same; in particular, the altitude (orbital period) that enables the resonance with ICESat 2. The orbital change consists, firstly, of a decrease in semi-major axis (altitude), which introduces an along track drift towards orbital positions ahead of the current one. This is then followed by another set of manoeuvres to recover the original altitude, stopping the along track drift, and reaching its final position. The duration of the manoeuvre campaign is a parameter inversely linked to the cost of the orbital change in terms of propellant mass, which implies a trade off between these two variables. Following the same approach as in the latest orbital change, a reference orbit dedicated to mission planning will be generated for the transitory period. This will allow keeping the SIRAL instrument active during most of the manoeuvre campaign.

CryoSat-2 is ESA's first satellite mission dedicated to measuring changes in the cryosphere and its measurements have transformed our capacity to study the polar regions. Thanks to CryoSat-2, we now have an altogether new appreciation of how Earth’s ice sheets, ice shelves, sea ice, glaciers, and polar oceans are evolving. As global temperatures have risen, so too have rates of snowfall, ice melting, and sea level rise, and each of these changes impacts upon the neighbouring land, marine, and atmospheric environments. CryoSat-2 measurements are now central to our awareness and understanding of Arctic and Antarctic environmental change; a case in point is the marine ice sheet instability that is underway in West Antarctica, widely understood to be among the greatest contemporary imbalances in the climate system, whose evolution has been charted in satellite altimeter data since its onset. In this presentation I will introduce the CryoSat-2 mission concept, describe the technical advances that have improved our capability to monitor land ice, sea ice, and the polar oceans, and review a series of flagship studies that have allowed both long-standing and unanticipated scientific problems in cryospheric research to be solved.