Monitoring sea level using GPS : the difference between the Mediterranean and the Red Sea levels as a test case
Ben-Michael, Chai & Gilad Even-Tzur
The maritime distance between Tel-Aviv and Eilat is thousands of kilometers, while the ground distance is about 400km. In such a case, the height difference between the two seas can be obtained from tide gauges situated along the shores and precise leveling between the tide gauge benchmarks. This approach besides being very expensive and notoriously time consuming is also expected to deliver height difference accuracy level of decimeter level for such a distance. GPS is a tool that can easily and quickly solves vectors longer then 400km with centimeter level of accuracy and can measure point height changes relative to the reference ellipsoid WGS84. Although in the past two decades GPS penetrated massively almost every field of geodetic measurements, it is still almost not in use in the field of sea level assessment. Attempts of using GPS equipped buoys for the determination of precise sea level (at centimeter level) were successful and suggest that if carefully used, GPS is capable of replacing the conventional tide gauges. The paper describes the development of a GPS based tide gauge (GPTG) prototype and its successful operation. Two field tests were carried out, the first one was a proof of concept, and demonstrated measurement ability with the accuracy of close to 1cm. The second test was carried out with a goal for determination the capacity of the GPTG to connect two distinct tide gauges, and its ability to measure accurately the level difference between the two distinct bodies of water - the Red Sea and the Mediterranean Sea. Examining the results of the prototype test and the second test resulted in a conclusion that the use of a GPS based Tide Gauge system for the determination of sea level changes is possible, and that its accuracy level (averaged) is equal to a float based tide gauge. More than that, an absolute change of sea level should be easier to be determined by the GPTG.
Event: XXIII International FIG Congress : Shaping the change
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