CryoSat-2/Sentinel-3/SMOS Merged Sea Ice Thickness

Documentation

Product description document

Read-me-first technical note

Version Log

v300 - 15.10.2025 (Major System and Algorithm Update)

• New production system: The algorithm as well as the input and output data handling are now fully implemented in a new python-based software.
• New input data: Sea ice thickness derived from Sentinel-3A (since October 2016) and Sentinel-3B (since October 2018) has been incorporated into the optimal interpolation process. The sea ice thickness measurements generated by Sentinel-3A/B utilize the AWI v2.6 sea ice freeboard and thickness retrieval algorithm and are fully consistent with CryoSat-2 data.
• Regional Extension: CS3SMOS is now also generated for the southern hemisphere during the austral winter (April 15 – Oct 15).
• Enhanced Spatial Resolution: The CS3SMOS data for both the northern and southern hemispheres is produced with a spatial resolution of 12.5 km, whereas the CS2SMOS data was generated with a spatial resolution of 25 km.
• Updated SMOS input data: The SMOS sea ice thickness data input version has been upgraded from version 3.3 to 3.6.
• Radar Altimeter Data Gridding: The aggregation of radar altimeter data (CryoSat-2 & Sentinel-3A/B) is now longer implemented in the CS3SMOS data merging. Instead, the aggregation to daily grids is handles within the AWI v2.6 sea ice production system.
• Updated Uncertainties: The optimal interpolation is now based on updated uncertainties in the radar altimeter (CryoSat-2 & Sentinel-3A/B) and L-Band passive microwave (SMOS) sea ice thickness datasets.
  • Radar Altimetry: The CryoSat-2 and Sentinel-3A/B uncertainty computation generated by the AWI v2.6 retrieval algorithm includes the different effect of systematic and random uncertainty components. The resulting grid uncertainty is substantially higher compared to the uncertainty from gridding l2p CryoSat-2 data in the CS2SMOS v2.6 algorithm.
  • L-Band Radiometry: The uncertainty in SMOS for optimal interpolation differs from the sea ice thickness uncertainties provided in the SMOS v3.6 L3C datasets. Instead, the uncertainty contribution from deviations in 100% sea ice concentration is incorporated into the SMOS sea ice thickness uncertainty, which is also capped at a minimum value of 20 cm. This approach ensures a similar magnitude of uncertainty relative to radar altimeter data. Without this adjustment, SMOS sea ice thickness would be overly weighted in the optimal interpolation process.
• New land/ocean mask: The land/ocean mask has been changed to match the one used in ESA CCI sea ice products. It also includes
• New File Structure: The output file structure has been simplified to include only the most relevant geophysical parameters required for computation of sea ice volume. Newly added variables include the fraction land/ocean mask as well as status and quality flags.

v206 - 15.10.2023 (System Update)

We updated the CS2SMOS processing to the latest input versions of the source data (SMOS L3C sea ice thickness v3.3 & CryoSat-2 L2P sea ice thickness v2.6)

CryoSat-2 version 2.6 update

• Reprocessing with CryoSat-2 ICE Level-1b algorithm baseline-E (in v2.5, baseline-E data was only used since Oct 2020).
• Use the OSI-SAF / C3S sea ice type (interim) climate data record. Notable changes in sea ice type information in the first half of October. 
• Resolved issues´:
  • There have been cases of incomplete CryoSat-2 near real-time L1B data on the production system in v2.5. The latency of near real-time production has been increased from 36h to 48h

(full change log)

CS2SMOS algorithm changes

• None

v205 - 15.10.2022 (System Update)

We updated the CS2SMOS processing to the latest input versions of the source data (SMOS L3C sea ice thickness v3.3 & CryoSat-2 L2P sea ice thickness v2.5)

CryoSat-2 version 2.5 update

• New surface type classification (sea ice / lead / open ocean discrimination)
• New flag indicating surface wave / swell influence in the marginal ice zone
  
• Resolved issues:
  • Waveform shape parameter computation used for surface type (lead, sea ice) discrimination incorrect for noisy waveforms
  • Not all orbit segments from different files were connected correctly

(full change log)

CS2SMOS algorithm changes

• Apply CryoSat-2 marginal ice zone filter flag in CS2SMOS data merging

v204 - 15.10.2021 (System Update)

We updated the CS2SMOS processing to the latest input versions of the source data (SMOS L3C sea ice thickness v3.3 & CryoSat-2 L2P sea ice thickness v2.4)

CryoSat-2 version 2.4 update

• Latest CryoSat-2 L1B data version (ICE baseline-E from Oct. 2021 and later, ICE baseline-D until April 2021)
• latest version of OSI-SAF sea ice concentration and sea ice type auxiliary data,
• change of sea ice concentration mask from 70% to 15%)

(full change log)

SMOS version 3.3 update

• Latest SMOS L1C data version (v724)
• Grid: NSIDC Sea Ice Polar Stereographic North (EPSG:3411) has been replaced by WGS 84 / NSIDC Sea Ice Polar Stereographic North (EPSG:3413)

(full change log)

CS2SMOS file format changes

• Minor update of global attributes

v203 - 15.10.2020 (System update)

• We adapted the CS2SMOS processing to changes due to the update to CryoSat-2 sea ice thickness product version v2.3. 

v202 - 15.10.2019 (System and algorithm update)

• The time coverage resolution has been changed from 7 days to 1 day, meaning that the weekly averaged product is updated every day from now on.
• We adapted the CS2SMOS processing to changes due to the update to CryoSat-2 sea ice thickness product version v2.2. 
• We adapted the CS2SMOS processing to changes due to the update to SMOS sea ice thickness product version v3.2, which is now processed and provided by AWI.
• An ocean mask is applied to allow for a consistent land/ocean mask throughout the entire data record in order to overcome inconsistencies due to switches of the land masks in the OSI SAF ice concentration products.
• We now use different sea ice concentration products for the operational mode and for the reprocessing mode. In the operational mode, we use the operational OSI-401 ice concentration product, while in the reprocessing mode, the reprocessed OSI -430-b ice concentration product is used. Both are provided by OSI SAF.
• Changes in the NetCDF variable names, fulfilling CF 1.6 conventions.

v201 - 10.01.2019 (Official ESA release)

Initial release