Microwave remote sensing of polar sea ice (SMOS, SMAP and follow-ons) (2010–present)

1. SMOS launched with L-band radiometer

   Nov 2, 2009Labels: SMOS, L-band radiometer, ESA

   ESA launched the Soil Moisture and Ocean Salinity (SMOS) satellite to map soil moisture and ocean salinity using an L-band (1.4 GHz) microwave radiometer. Soon after launch, researchers recognized that the same low-frequency microwave signals could also help estimate thin sea-ice thickness, because L-band can sense deeper into young ice than higher-frequency sensors. This created a new pathway for satellite monitoring of seasonal sea ice growth.

   • ESA Timeline
   • ESA SMOS
   • ESA Sea ice

2. CryoSat-2 launched for sea-ice thickness

   Apr 8, 2010Labels: CryoSat-2, radar altimetry, ESA

   ESA launched CryoSat-2 to measure ice thickness using radar altimetry, a method that estimates thickness from the height of ice above the ocean (freeboard). CryoSat-2 is strongest for thicker ice, while SMOS is more sensitive to thin ice. Together, the missions set up a complementary space-based approach to sea-ice thickness across a wider range of conditions.

   • ESA Sea ice
   • CryoSat 2

3. CS2SMOS merged thickness product begins (Arctic winters)

   Nov 1, 2010Labels: CS2SMOS, Alfred Wegener, merged product

   Teams led by the Alfred Wegener Institute (AWI) and partners began producing a merged CryoSat-2 + SMOS sea-ice thickness product (often called CS2SMOS). The blend uses CryoSat-2 for thicker ice and SMOS for thinner ice, improving coverage and reducing uncertainty for thin-ice conditions. This marked a practical step from “two complementary missions” to a combined monitoring system.

   • TCD CS2SMOS
   • ESA Catalog

4. SMOS-based Arctic thin-ice mapping demonstrated

   Oct 5, 2012Labels: SMOS, Arctic thin, ESA research

   ESA-supported research showed SMOS could estimate sea-ice thickness for thin, newly formed ice (roughly up to about 0.5 m). This mattered because thin ice can grow or melt quickly and strongly affects heat exchange between the ocean and atmosphere. The work helped turn SMOS from a “bonus capability” for ice into a usable research tool for seasonal sea-ice monitoring.

   • ESA Sea ice

5. SMAP launched with L-band radar and radiometer

   Jan 31, 2015Labels: SMAP, L-band radiometer, NASA

   NASA launched the Soil Moisture Active Passive (SMAP) satellite with an L-band radiometer and an L-band radar. Although designed for land and hydrology, its L-band measurements also offered opportunities for cryosphere work, including sea-ice and freeze/thaw studies. SMAP added a major new L-band data stream that could be compared with and used alongside SMOS.

   • SMAP News
   • SMAP

6. SMAP radar failure shifts focus to radiometer

   Jul 7, 2015Labels: SMAP, radiometer only, instrument anomaly

   SMAP’s radar stopped transmitting due to an anomaly, ending planned “active-passive” combined measurements from the mission. The radiometer continued operating, preserving the passive L-band record that is also relevant for polar applications. The failure increased the importance of robust passive-microwave approaches and multi-mission strategies rather than relying on one instrument type.

   • SMAP News
   • NASA APPEL

7. CS2SMOS product evaluated against field campaigns

   May 3, 2019Labels: CS2SMOS, field campaigns, validation study

   A detailed assessment compared several satellite sea-ice thickness products with independent measurements such as upward-looking sonar and Operation IceBridge. The study found CryoSat-2-only products were generally reliable for mid-range thickness, while a blended CryoSat-2 + SMOS product performed especially well for thin ice. These evaluations helped users understand which products fit which scientific and operational needs.

   • TCD Study

8. Copernicus Marine adds near-real-time merged thickness

   Mar 31, 2020Labels: Copernicus Marine, near-real-time product, merged thickness

   The Copernicus Marine Service released an improved near-real-time sea-ice thickness product that benefits from SMOS data and merges information from different satellites (including CryoSat-2 and SMOS). This mattered for operational users because near-real-time products support timely decision-making for Arctic shipping, safety, and environmental monitoring. It also signaled that L-band sea-ice methods had matured into routine services.

   • Copernicus
   • TCD CS2SMOS

9. ESA signs CIMR development contract (Copernicus Expansion)

   Nov 19, 2020Labels: CIMR, ESA, Copernicus Expansion

   ESA signed the development contract for the Copernicus Imaging Microwave Radiometer (CIMR), designed to improve routine microwave measurements over oceans and sea ice. CIMR is planned to deliver frequent revisits over polar regions with high-resolution sea-ice observations using a conically scanning, multi-frequency microwave radiometer. This step connected lessons from SMOS/SMAP-era L-band work to a next-generation operational mission concept.

   • ESA Contracts
   • ESA CIMR

10. CIMR launch dates published for first two satellites

    Oct 3, 2023Labels: CIMR-A, CIMR-B, ESA mission

    ESA mission information for CIMR outlined planned launch dates for two satellites (CIMR-A and CIMR-B), reflecting a move toward sustained, repeat coverage rather than single-satellite dependence. The plan emphasizes rapid revisits in the Arctic and broad daily global coverage, supporting more stable time series for sea ice and ocean variables. This helped define the likely “follow-on” path after SMOS/SMAP-era breakthroughs.

    • ESA CIMR
    • ESA Image

11. Microwave sea-ice monitoring framed as continuous system

    Jun 1, 2024Labels: Copernicus, CIMR, operational monitoring

    Copernicus communications highlighted CIMR’s role in improving spatial and temporal coverage for Arctic sea ice and related ocean variables. This framing reflects a shift from “research demonstrations” (like early SMOS sea-ice thickness retrievals) toward long-term operational readiness and user-driven requirements. It also reinforces the idea that polar sea-ice monitoring relies on multi-sensor continuity and planned replacements.

    • Copernicus
    • ESA CIMR

12. Planned CIMR-A launch as next major follow-on

    Jan 1, 2029Labels: CIMR-A, follow-on mission, planned launch

    CIMR-A is planned to launch as the first CIMR satellite, aiming to provide frequent, high-coverage microwave observations over polar oceans. If delivered as planned, CIMR would extend and strengthen the passive-microwave record that SMOS and SMAP helped prove valuable for sea ice. This marks the expected next transition point from the 2010s “SMOS/SMAP era” to a new generation of operational polar microwave radiometry.

    • ESA CIMR