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CryoSat-2 is a European Space Agency (ESA) Earth Explorer Mission that launched on April 8th 2010. CryoSat-2 is dedicated to measuring polar sea ice thickness and monitoring changes in ice sheets. Its primary objective is to measure the thinning of Arctic sea ice, but has applications to other regions and scientific purposes, such as Antarctica and oceanography.

CryoSat-2 was built as a replacement for CryoSat-1, which failed to reach orbit following a launch failure in October 2005. CryoSat-2 was successfully launched five years later in 2010, with upgraded software aiming to measure changes in ice thickness to an accuracy of ~10% of the expected interannual variation. Unlike previous satellite altimetry missions, CryoSat-2 provided unparalleled Arctic coverage, reaching 88˚N (previous missions were limited to 81.5˚N). The primary payload of the mission is a synthetic aperture radar (SAR) Interferometric Radar Altimeter (SIRAL), which measures surface elevation. By subtracting the difference between the surface height of the ocean and the surface height of sea ice, the sea ice freeboard can be calculated, and converted to sea ice thickness.

CryoSat-2 is part of ESA's wider CryoSat mission in the Living Planet Programme.

Original Objectives
The aim of the CryoSat-2 mission is to determine ice thickness variations on Earth's ice sheets and marine ice cover. Its primary objective is to measure Arctic sea ice thickness, testing the hypothesis that Arctic sea ice is thinning due to climate change. Furthermore, the mission aimed to monitor ice thickness changes in Antarctica and Greenland, to determine their contribution to sea level rise. The mission objectives can be summarised as:


 * Determine trends in Arctic sea ice thickness
 * Determine the contribution that Antarctica and Greenland are making to sea level rise
 * Observe variability in Arctic and Antarctic sea ice thickness
 * Observe changes in the thickness of Earth's ice caps and glaciers

Extend Objectives
CryoSat achieved its initial mission objectives following the launch of CryoSat-2, and therefore the mission was extended with new objectives.


 * Assess the spatial and temporal variability of ice sheet margins, glaciers, and ice caps
 * Investigate oceanic variations in the Polar regions
 * Examine product contribution to operational and forecasting services
 * Extend the current data record to ensure mission continuity
 * Assess how snow fall and surface ice melting contribute to cryosphere meteorology
 * Retrieve sea ice thickness measurements in Antarctica oceans
 * Observe inland water variations

SIRAL
The primary payload onboard CryoSat-2 is the SAR Interferometric Radar Altimeter (SIRAL), operating in the Ku-band (13.6 GHz). The instrument combines a pulse-limited radar altimeter and a second antenna with synthetic aperture and interferometric signal processing. SIRAL has a pulse bandwidth of 320 MHz. The instrument operates in three modes depending on the surface type being measured; low resolution mode (LRM), synthetic aperture radar (SAR) mode, and SAR interferometric (SARIn) mode. LRM is used over ice sheet interiors and oceans, SAR is used over sea ice and possible oceanographic areas, and SARIn is used around the ice sheet margins and mountain glaciers.

LRM
LRM operates in a conventional, pulse-limited mode; the area of surface seen by the instrument is limited by the length of the radar pulse transmitted by the altimeter. A single antenna transmits and receives the radar signal. This mode ensures returning echoes are uncorrelated.

The LRM footprint is approximately 1.7 km. The pulse repetition frequency in this mode is 1.97 kHz.

SAR
In SAR mode, SIRAL emits a burst of 64 pulses, separated into narrow along-track beams by exploiting the Doppler Effect. Each strip is ~250 m wide, and the interval between bursts means each ground location is measured multiple times, improving accuracy.

The SAR footprint is approximately 0.31 km along-track and 1.67 km across-track. The pulse repetition frequency in this mode is 18.181 kHz.

SARIn
In SARIn mode, the two antennae are used to account for surface slope. The two antennae, mounted 1 m apart, receive the echo almost simultaneously. If the return signal returns from off-nadir, then it is possible to measure the angle between the baseline and echo direction, therefore estimating surface slope.

DORIS
The Doppler Orbit and Radio Positioning Integration (DORIS) is the second instrument on CryoSat-2, and calculates precisely the space...

Results
CryoSat-2 successfully achieved the CryoSat mission objectives.

Sea ice thickness measurements have been produced by the Centre for Polar Observation and Modelling (CPOM), the Alfred Wegener Institute (AWI), and NASA's Jet Propulsion Laboratory (JPL) and the Goddard Space Flight Center (GSFC). Arctic sea ice thickness data are available to view and download from CPOM.

The Centre for Polar Observation and Modelling (CPOM) is a Natural Environment Research Council (NERC) Centre of Excellence that studies processes in the Earth's polar environments. CPOM conducts research on sea ice, land ice, and ice sheets using satellite observations and numerical models.

CPOM has scientists based at the Universities of Leeds, Bristol, Reading, Lancaster, Swansea, and University College London. CPOM also has partnerships with several other institutions, including the British Antarctic Survey (BAS), the National Oceanography Centre (NOC), the National Centre for Earth Observation (NCEO), the European Space Agency, and the Met Office.

History
The Centre for Polar Observation and Modelling was founded in 2000 by Professor Sir Duncan Wingham.

Directors
Professor Sir Wingham was director of CPOM from 2000 to 2005, and his expertise in Earth's ice sheets led to reports on the widespread mass loss from the west Antarctic Ice Sheet. He was also Project Scientist of the European Space Agency's CryoSat mission. He has since been appointed as NERC Chief Executive. Professor Sir Wingham was awarded a Knighthood in 2019 for services to Climate Science.

Professor Sir Wingham was succeeded as CPOM Director by Professor Seymour Laxon. Professor Laxon was an expert on satellite radar altimetry, and his work pioneered the use of satellite altimetry to measure sea ice thickness and surface circulation in polar oceans. This work would lead to the successful development of the European Space Agency's CryoSat mission. Sadly, Professor Laxon died following an accident in 2013.

The role of CPOM Director was succeeded by Professor Andrew Shepherd. Professor Shepherd is an expert in remote observations of the Cryosphere, and is Principal Scientific Advisor to the European Space Agency's CryoSat mission, and co-leader of the Ice Sheet Mass Balance Inter-comparison Exercise.

Research
Recent notable publications from CPOM scientists that garnered significant media attention include:


 * In 2022, researchers from CPOM and BAS found that mega iceberg A68 had released 152 billion tonnes of freshwater into the ocean around South Georgia.
 * In 2021, CPOM researchers named glaciers in the Getz region of Antarctica after international climate conferences, including Glasgow for COP26.
 * CPOM researchers reported in 2021 that Arctic sea ice is thinning twice as fast as previously thought.
 * In 2021, a review by CPOM researchers into the state of Earth's ice showed that between 1994 and 2017, Earth lost 28 trillion tonnes of ice.
 * Researchers from CPOM in 2020 found that ice sheets in Greenland and Antarctica are melting at a rate which matches the worst-case scenario for sea level rise.
 * In 2020, researchers from CPOM found a six-fold increase in polar ice losses since the 1990s.