1. Recent Activities of Ocean Surface Topography Virtual Constellation (OST-VC)
Remko Scharroo (EUMETSAT)

2. OST-VC Cal/Val Activities — Background
Three satellite altimeter launches since 2016
Jason-3 (Jan 2016)
Sentinel-3A (Feb 2016)
Sentinel-3B (Apr 2018)
Long-term (25+ years) altimeter record
Cross-calibration
In-situ data
Various initiatives and projects

3. Jason Cal/Val Activities (1)
In-orbit verification, calibration and validation
Conducted largely by Partner Agencies (CNES, NASA, NOAA, EUMETSAT)
Decision making on data release to OSTST and wider community
Ocean Surface Topography Science Team (OSTST)
Wide range of scientists and operational users with interest in Jason missions
Sponsored by all Jason Partner agencies
Is expanding to become a multi-mission international working group on all altimeter missions
Mission-long cal/val activities
Suggestions for evolutions of algorithms and auxiliary data

4. Jason Cal/Val Activities (2)
Jason-2 end-of-life activities
Small group of experts made recommendations to optimise between constellation needs and science output
Decision making by Joint Steering Group (Partner Agencies)

5. Sentinel-3 Activities (1)
In-orbit verification, calibration and validation
Conducted largely by Partner Agencies (ESA, EUMETSAT, CNES)
Decision making on data release to S3VT and wider community
Sentinel-3 Validation Team (S3VT)
Wide range of scientists and operational users with interest in Sentinel-3
Meet approximately yearly to present cal/val activities
Also suggestions for future evolutions of algorithms and auxiliary data

6. Sentinel-3 Activities (2)
Sentinel-3 Quality Working Group (S3QWG)
Select group of key scientists on various aspects of satellite altimetry:
Sea level, sea ice, land ice, winds and waves
Report of quality analysis
Recommend evolutions to Partner Agencies
OSTST
Has over the last years starting to morph into a multi- mission altimeter working group

7. Sentinel-3 Activities (3)
CEOS OST-VC Highlight
At time of Sentinel-3A launch it was planned to launch Sentinel-3B straight into its interleaved orbit
So no tandem mission
ESA and EUMETSAT with the help of OST-VC recommended to management to have a tandem mission first
Common to previous altimeter missions for long-term record
Unique for optical instruments
Already paying off in detecting small inter-satellite (processing) differences

8. FRM4ALT: Fiducial Reference Measurements for Altimetry
International Review Workshop (April 2018)
Critical review of methodology
Cal/Val using ground-based measurements
Define requirements, establish standards
Calibration such that sea level can be monitored under international standards
Roadmap
Establish reference frame
Minimum set of observations
Harmonised approach with continuous capability
Requirements on in-situ equipment
Transponder, tide-gauges, radiometer

9. SAOO Phase 0 study
CNES Phase 0 study for new (swath) altimeter constellation
Based on requirement to resolve 50 km & 5 days resolution
Leads to either D altimeters or 2-3 swath altimeters
Still needs “traditional” 1-D altimeters for reference
Study can be expanded to white paper on future altimeter constellation
Based on up-to-date requirements on
Spatio-temporal coverage
Accuracy
Long-term stability
Intended as OST-VC activity for next 2 years