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Sea level and GPS projects in Hong Kong and East China Sea

Sea level and GPS projects in Hong Kong and East China Sea. H. Bâki Iz and C.K. Shum The Hong Kong Polytechnic University and The Ohio State University. Motivation. Assessing the quality of the existing tide gauge data

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Sea level and GPS projects in Hong Kong and East China Sea

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  1. Sea level and GPS projects in Hong Kong and East China Sea H. Bâki Iz and C.K. Shum The Hong Kong Polytechnic UniversityandThe Ohio State University

  2. Motivation • Assessing the quality of the existing tide gauge data • Error analysis for the estimation of the MSL change using long term tide gauge data • Assessing the site stability and its impact to the solution

  3. Tide Gauge Stations in Hong Kong

  4. Comparison of 15-year monthly MSL(North Point, Tai Po Kau, Chin Ma Wan tide gauge stations)

  5. Periodic MSL variations as revealed by tide gauge observations and satellite altimetry data

  6. Tide Gauge setup at Quarry Bay (formerly located at the North Point location)

  7. Variation of hourly tide gauge data at North Point Station at sampled days

  8. Variate differencing for estimating the random errors in the tide gauge data If we have series that can be represented locally by a series of polynomials (systematic variations) with superimposed random elements, the polynomial part can be eliminated by a series of successive differencing of the series.

  9. Daily random errors estimated byvariate differencing1978 values from the North Point station 1997 values are from the Quarry bay stationThe same tide gauge was used in both stations

  10. There are surprises! • Tide gauge station at the North Point station and subsequently at the Quarry Bay were located in the reclamation areas! • Episodic leveling results show settlement of the RMs

  11. Settlement of the RM at the North Point station

  12. Math model for the RM stability at North Point Station

  13. Stat model for the RM stability (North Point)

  14. Model for estimating the change in the MSL as function of time from the tide gauge data

  15. The uncertainty of the estimated MSL yearly variations from RM settlement corrected tide gauge data

  16. Total uncertainty of the to be estimated MSL rate of change as a function of number of years of observation

  17. What can we detect?

  18. More surprises • At Quarry Bay station, BM that was used to check the stability of the RM also exhibit settlement in time. • Episodic leveling results show also settlement of the RM.

  19. Bench mark stability at Quarry Bay station

  20. Settlement of the RM at the Quarry Bay Station

  21. Conclusion • Limiting factors: not the stability of the RM and BM but how accurately we can detect them. • The use of GPS should be carefully examined (potential problem areas: long term systematic variations due to the ionospheric effects, orbit drift, and reference frames) • Need for accurate modeling of periodic variations for calibrating altimeter borne data.

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