The launch date of the Copernicus polar Ice and Snow Topography ALtimeter (CRISTAL) is planned in 2025. To assess the performances of the future constellation, it is of major importance to identify all the altimetry mission components, along with their characteristics. This is mandatory to conceive the most relevant satellite payload and define an adequate orbit to address efficiently the user requirements. The following figure displays a view of the current and future altimetry constellations:

The significant numbers are summarized below regarding the altimetry constellation predicted for 2025:

  • All in all: at least 5 altimeters are expected to be in operation.
  • 3 missions in SAR mode (Sentinel-6A + Sentinel-3C/D); 3 missions in LRM (Sentinel-6A, HY2 C/D). All missions in Ku band.
  • 1 mission on the reference Jason orbit (Sentinel-6A); 2 Sentinel-3 missions on the 35-days orbit cycle of ERS/Envisat/ALtiKa; 2 HY missions on a 14-days orbit cycle.
  • The maximum geographical coverage will be up to +/- 82° only, leaving a big gap of observation up to the pole.

The following figures show the geographical coverages of the current (top) and probable future (2025-2030 period, bottom) missions over polar areas:

Current altimetry constellation

Planned 2025-2030 altimetry constellation

Note: Hatched areas are not covered by any altimetry missions

In summary

The main gaps relative to the 2025 constellation are the following:

Sea-ice surface: 

  • Lack of measurements beyond 81.5°N/S
  • Uncertainty in sea-ice thickness estimates due to uncertainty in snow load and ice type
  • Limitation of sea-ice thickness retrieval to winter months only

Ice sheet surface: 

  • Lack of measurements beyond 81.5°N/S
  • A lack of continuous coverage of ice sheet margins
  • A lack of accuracy in coastal regions with complex topography, due to an absence of interferometric Synthetic Aperture Radar (SAR) altimeter measurements
  • A demand for greater precision in resolving small elevation changes across large inland areas of the ice sheets.

Ocean surface: 

  • lack of coverage of the Arctic Ocean, where lot of uncertainties remain. In particular: the mean sea surface, the mean sea level trend, mesoscale circulation, oceanic tides, wind & wave forecast.