Evaluation of orbit candidates
Different diagnoses were performed over the three surfaces:
- Ice charting sampling & weekly products capability for sea-ice (performed by Lancaster University)
- Monthly & quarterly products capabilities for ice sheets (performed by Finnish Meteorological Institute)
- Decorrelation of mesoscale signals in space/time & polar ocean analysis for ocean. Polar ocean analysis originating from G.Dibarboure (Centre Nationale d’Etudes Spatiales – CNES)
- A global sub-cycle analysis (performed by CLS)
The complementarity with Sentinel-3 was also analysed. The results were presented to the MAG members. The table below provides a summary of the results. The orbit candidates were ranked in the table as optimal (dark green), sub-optimal (light green) ; average (yellow) and not adapted (red).
Orbit evaluation summary table: optimal (dark green), sub-optimal (light green) ; average (yellow) and not adapted (red).
When Sentinel-3 is added in the orbit analyses, all orbit candidates are optimal for ice sheet & sea ice surfaces, and thus fulfil the user requirements.
- For sea-ice, best candidates are Case-1 ; Case-5 ; CLS1 & CLS3, thanks to the 7 days sub-cycle
- For ice-sheets, best candidates are:
- ICESat-2 if total coverage over an annual cycle is deemed to be not important
- Case-5, CLS1, CLS2, CLS3 if annual coverage is important. Case-5 providing the best performances for monthly sampling. CLS1, CLS2, CLS3 very close with a better quarterly sampling
- For ocean, best candidates are Case G2 ; CLS1 & CLS2 as they provide the most efficient sampling of oceanic mesoscale signals, and are adapted for a polar mesoscale multi-mission strategy. Case-5 is the worst.
Overall, the CLS1 orbit seems to be the best among all the orbit candidates when requirements for oceanography (polar mesoscale and global mesoscale) are taken into account.
The studied orbits, or at least a subset of the 8 orbits, would undergo a technical feasibility analysis (station visibility, altitude conflicts etc.) as well as ESA orbit experts. Since all orbits generally fulfil the performance and application needs (except Case-5 orbit), the orbit candidate with the best suitability to these user requirements as well as the technical constraints should be selected and presented to the MAG.