Lecturer of Engineering Geodesy at Universitas Diponegoro, L.M. Sabri, has earned a doctoral degree in Geomatics Engineering from UGM on Friday (7/27).
Sabri received the degree after defending his dissertation titled Vertical Reference System in Areas of Land Subsidence (A Case Study: Semarang) during a doctoral public examination at Faculty of Engineering UGM.
On that occasion, he stated land subsidence that occurred in Indonesia, including Semarang, caused infrastructure damage. In fact, it also caused changes in levelling-based vertical datum as altitude measurement reference for infrastructure planning, development, and maintenance.
“Elevation changes of levelling-based vertical datum result in degradation of accuracy as well as measurement efficiency,” he said.
Sabri mentioned the accuracy and efficiency of elevation measurement in areas of land subsidence can be improved by combining GNSS measurement with geoid-based vertical datum. Low precision and distribution of gravity data, geodetic coordinates, and physical altitude hold the precision of gravimetric geoid in Indonesia within decimeter level.
Another issue is the accuracy of physical elevation measurements with orthometric height system in Indonesia that is not supported by accurate rock density data. Meanwhile, in European countries, accurate physical height is obtained by applying the normal height system that is not yet popular in Indonesia.
This encouraged Sabri to conduct research to obtain a precise gravimetric geoid model, height system, and gravimetric geoid-based vertical datum for land subsidence areas.
Result of the research showed that gravimetric geoid models that coincided with the National Vertical Control Network could be used to convert altitude from GNSS measurement to normal height quickly and accurately.