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.