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CPOM@EGU26 Blog – Polarimetric Synthetic Aperture Radar Altimeter concept (PoSARA): The Bold Idea That Could Change How We Monitor Sea Ice

The thicknesses of sea ice and the snow that rests upon it are recognised as Essential Climate Variables by the WMO, critical for understanding, monitoring, and predictions of Earth’s climate. However, snow depth on sea ice is difficult to measure by satellite due to how radar penetrates and scatters off the ice, presenting challenges for assessing sea ice thickness.

The challenges surrounding quantifying this variable can have knock on considerations for monitoring ice mass balance, understanding of polar climate feedbacks, the operational safety of shipping routes, and ecosystems. As snow depth on sea ice is dynamic and precipitation and snow pack properties can evolve through seasons as well as varying over longer timescales due to warming, the gap in understanding could become increasingly consequential over time.

A discovery with the KuKa radar was developed into a novel snow depth retrieval approach. KuKa can be operated looking straight down (using Altimeter mode); and looking at an incidence angle (using Scatterometer Mode); both provide can both waveforms and normalised radar cross section values. Scientists have found that polarisation can help to determine snow depth on Arctic and Antarctic sea ice, which would also support estimations of sea ice thickness.

On Friday 8 May, Dr Rosemary (Rosie) Willatt (UCL) will present at EGU26 on the progress of the Polarimetric Synthetic Aperture Radar Altimeter concept (PoSARA) — a novel satellite instrument concept using polarimetric capability to estimate snow depth on sea ice, land ice and land from space. She will share with the audience how well the technique works over Arctic and Antarctic sea ice, lake ice and Arctic tundra, derived from multiple field campaigns.

“Making the unexpected discovery that using polarisation of waveforms provided accurate estimates of snow depth on sea ice in the initial MOSAiC dataset was exciting – nobody had predicted it but it made sense given existing theory on depolarisation in snow and we found one example of another instrument which observed something similar over a glacier. We then found our approach also worked with KuKa data from the Southern Ocean, and over tundra and lake ice in Churchill and Resolute.” – Said Rosie, commenting on the project for CPOM.

The team has developed the concept through to Scientific Readiness Level (SRL) 3 as part of ESA’s NEOMI initiative (New Earth Observation Mission Ideas). NEOMI aims to scientifically advance new Earth Observation mission ideas, empowering emerging scientists as lead investigators for potential future satellite missions and bold new EO research, and to formulate and develop a new scientific idea for an Earth Observation mission up to SRL 3.

Rosie, who is also CPOM’s Principal Investigator (PI) for Sea Ice Earth Observation, was awarded the ESA inaugural Konrad Steffen Award for a presentation on the early stages of this work, and is PI of the project, developing the concept for space application.

The science behind it has been actively tested in the field more recently too. In April 2025, an all-female field team of polar scientists from CPOM and UCL, including Rosemary Willatt, Julienne Stroeve, Carmen Nab and Alicia Fallows, visited Resolute Bay to investigate the use of this frequency radar and different polarisations on ice and snow.

You can watch a video the team made about the fieldwork here: https://cpom.org.uk/testing-kuka-in-the-arctic-new-video/

Satellites observing Earth’s polar regions give scientists the information they need to monitor how ice sheets and sea ice are changing, quantify their contribution to rising seas, and better understanding the complex ways that melting ice reshapes global weather systems.

Read the abstract and find out more about this ‘Highlight’ presentation on the EGU26 website.

Header image credit: Professor Alison Banwell

Feature image credit: Dr Amy Swiggs