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The Offset of the South Korean Vertical Datum from a Global Geoid
Christopher Jekeli,양효진,권재현 대한토목학회 2012 KSCE JOURNAL OF CIVIL ENGINEERING Vol.16 No.5
Accurate orthometric heights in a national vertical datum can be determined economically using GPS heights and gravimetrically computed geoid undulations. If this national vertical datum should be tied to a global geoid, then both the datum offset as well as the difference between the GPS ellipsoid and the globally best-fitting ellipsoid should be known. This paper elaborates on the theory and procedures to obtain the datum offset for South Korea’s national vertical datum on the basis of the global model, EGM08. Among several GPS/leveling data sets slightly different estimates are obtained, with the estimate, 26.5 +/- 1.3 cm (above the global zero-tide geoid) obtained using over 800 data points distributed in South Korea. The uncertainty is a level of precision, not absolute accuracy,and the discrepancies between estimates using different subsets of the data indicate the presence of small unsolvable biases among them. An alternative procedure to determine orthometric heights using the modern principles is also proposed that makes the vertical datum completely independent of the global geoid in the traditional way and obviates the estimation of these offsets.
Jekeli, Christopher,양효진,권재현 한국측량학회 2013 한국측량학회지 Vol.31 No.6
The determination of the geoid in South Korea is a national imperative for the modernization of height datums,specifically the orthometric height and the dynamic height, that are used to monitor hydrological systems andenvironments with accuracy and easy revision, if necessary. The geometric heights above a reference ellipsoid,routinely obtained by GPS, lead immediately to vertical control with respect to the geoid for hydrologicalpurposes if the geoid height above the ellipsoid is known accurately. The geoid height is determined fromgravimetric data, traditionally ground data, but in recent times also from airborne data. This paper illustratesthe basic concepts for combining these two types of data and gives a preliminary performance assessment ofeither set or their combination for the determination of the geoid in South Korea. It is shown that the mostcritical aspect of the combination is the gravitational effect of the topographic masses above the geoid, which,if not properly taken into account, introduces a significant bias of about 8 mgal in the gravity anomalies, andwhich can lead to geoid height bias errors of up to 10 cm. It is further confirmed and concluded that achievingbetter than 5 cm precision in geoid heights from gravimetry remains a challenge that can be surmounted onlywith the proper combination of terrestrial and airborne data, thus realizing higher data resolution over most ofSouth Korea than currently available solely from the airborne data.