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Geodetic Observations - Recommendations. 1. The International Terrestrial Reference Frame (ITRF) needs to be made more robust and stable over multi-decadal time scales. target accuracy is 0.1 mm/yr in the realization of the center of mass of the entire Earth system (“geocenter stability”),
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Geodetic Observations - Recommendations • 1. The International Terrestrial Reference Frame (ITRF) needs to be made more robust and stable over multi-decadal time scales. • target accuracy is 0.1 mm/yr in the realization of the center of mass of the entire Earth system (“geocenter stability”), • 0.01 ppb in scale stability, 0.6 mm/yr • This requires strong connections between the reference frames of the various geodetic systems
Geodetic Observations - Recommendations • The strong connections between the reference frames of the various geodetic systems require: • a. Implement more sites of every technique with a good (even) global distribution • b. Collocate different techniques • c. Sustain and evolve support for the scientific services (i.e., IERS, IGS, IVS, ILRS, IDS), • d. Place laser retro-reflectors on all future GNSS satellites, • e. Support Global Geodetic Observing System (GGOS) as the new paradigm • f. Conduct research into understanding biases • g. Conduct research towards improving tropospheric delay models.
Geodetic Observations - Recommendations • 3. Ensure long term stability and consistency in the measurements of sea level by altimetry and of mass by GRACE-type missions, • (a) analogues of current altimeter and gravity missions be continued indefinitely with sufficient overlap between missions, and with no gaps between missions; • (b) a world vertical datum be established • 4. Tide gauges be monitored for height variations using continuous GPS systems installed directly at the tide gauge • - additional tide gauges, co-located with GPS, be installed in areas with poor tide gauge coverage. • 5. Research and development of comprehensive Earth models that can assimilate all geodetic data types (including tide gauge data) that are relevant to determining sea level change. • At the next level, the models should be integrated with terrestrial hydrological models, cryospheric models, and ocean/atmospheric circulation models. • 6. In order to achieve the goal of determining sea level changes at the level of 0.1 mm/yr, support for the recommended systems and research activities must be brought up to a level capable of meeting that goal, and the support must at least be sustained for decades.
