1. Orbits converging this winter

When the Cryo2ice campaign began, the time difference between CryoSat and ICESat-2 measurements was around three hours, and ever since it has been getting closer and closer.

In the golden age of satellite altimetry, we might well be approaching the golden moment.

In February 2025, the orbits of the two satellites will be almost simultaneous.

Coincident measurements of ice from two satellites are particularly useful for monitoring sea ice. It moves, and conditions change. The closer the measurements are, the more accurate they will be.

No wonder they say CryoSat is the gift that keeps on giving!

2. Antarctic sea ice

In 2022, after two years of coincident orbits over the Arctic, CryoSat’s orbit was tweaked once again so that Cryo2ice would converge instead over Antarctica.

We had a bit of a decision to make this year, another two years on, as the plan had been to switch back to the Arctic.

However, we have decided to keep Cryo2ice aligned over Antarctica for now, and for good reason.

Antarctic sea ice is a particular challenge for cryosphere researchers. That is because the Antarctic and Arctic are very different dynamical systems. The Southern Ocean surrounds an entire continent, whereas Arctic sea ice sits atop an open ocean. That means sea ice behaves differently due to different weather and marine conditions.

Most of the sea ice surrounding Antarctica is also more seasonal, meaning that it melts away almost entirely in the summer in most regions. This ice is typically only one or two metres thick, and is warmer, full of snow, saltier, and moves a lot more than Arctic ice. All of this makes it particularly tricky to measure, and therefore model, from space.

In recent years, we’ve seen the Antarctic region alter much more rapidly than was predicted by climate models. Understanding it in greater detail will aid efforts to better predict the effects of climate change.

3. CRISTAL is coming

Many challenges remain in estimating ice thickness from space. Snow, for example, is a major source of uncertainty.

Why? The precise reasons are still being studied, but it is to do with the structure of the snow itself, and how that affects scattering of CryoSat’s radar signal, as well as differences between what remote sensing systems detect. Some detect the top of snow, others the top of ice, some between the two layers.

The future Copernicus Polar Ice and Snow Topography (CRISTAL) mission is set to tackle that with dual-frequency altimetry. Using radar measurements at two different wavelengths, which measure the top and bottom of the snow layer, it will be able to more accurately measure the depth of snow on ice.

Until then, we have to work with what we have. Luckily, what we have is pretty special, and together, CryoSat and ICESat-2 are already revealing a lot about snow on ice.

In a not-dissimilar way to dual frequency radar, ICESat-2’s laser signal mainly bounces back from the top of snow, while CryoSat’s radar penetrates through the snow to the boundary between snow and ice. In theory, we can better model snow depth by combining their measurements.

The first results from these coincident measurements over the Arctic arrived in Spring 2024, courtesy of Fredensborg Hansen et al. of DTU Space, highlighting the potential and challenges ahead for the CRISTAL mission.

4. Cryo2ice conference 

In September 2024 the Cryo2ice community gathers in Reykjavik to explore the achievements and future challenges of cryosphere research using CryoSat, ICESat-2, or both. The detailed programme has been published, which contains a treasure-trove of research covering mountain glaciers, ice sheets and ice shelves, sea ice, snow, ocean hydrology, and even beyond ice and snow. At the end of the session, we will also hear about the CRISTAL mission that will extend our long term satellite altimetry records of ice well into the 2030s.

5. CS2EO

There has never been more data for cryosphere researchers to get their hands on, but accessing, downloading, sharing and using it isn’t always so simple.

In May 2022, however, ESA, Earthwave and the University of Edinburgh released CS2EO, a “one stop shop for satellite altimetry data”, to improve that.

The platform builds on the Cryo2ice coincident data explorer to provide access to numerous datasets, including joint CryoSat and ICESat-2 data, Cryo-TEMPO and CryoTEMPO-EOLIS, as well as those from airborne campaigns such as Operation ICEBridge and CryoVEx.

Eight new datasets were added in the spring of 2024 to support, enhance, and simplify research, including the CryoSat Ocean Product, and the Cryo-TEMPO Land Ice, Sea Ice, Polar Ocean, Coastal Ocean and Inland Water datasets.

More exciting developments are underway, some of which will be shown at the Cryo2ice conference.