Establishment of the gravity level reference station

In the developed countries, such as the United States, Germany and Japanese etc., they all have established national gravity control system in the 19th, and 20th centuries and work toward to improvement. In order to establish international class national gravity control system, the ministry of Interior completed the Taiwan area absolute gravity points (Hsin Chu, Da Shi, Taichung, Gang San, Hwa Lien and Lu Shui) testing and class 1 gravity points construction work in 1999. Starting 2003, there is the five-year ¡§National Basic Measurement Development Program¡¨. Among them, in 2003, the plan is to purchase high precision gravity instruments as basis for the national gravity control system. It also seeks to include our national gravity level reference station into the international absolute gravity level reference net. (As shown in Diagram IAGBN, 2003).

Absolute gravity benchmark network

        The set up of national gravity base station shall be established on a gravity base that is stable and may be used for a long period of time. It is used as basis for the nation to proceed with gravity measurement. This gravity base is composed of gravity base net formed by many gravity points (include gravity base station). Among them, the gravity base station is the stable base station with high precision fixed type absolute gravity instrument for long term continuously 24 hour per day monitoring.

        In addition, to acquire high precision average seawater surface level, the key problem faced is the ever changing in tide that leads to the deformation of earth crust structure. Therefore, we must design a set of complete methods to remove these noises. Many researches point out that the measurement of absolute gravity is an effective tool to monitor the change in tide base level. The use of mGal class precision gravity instrument to measure gravity force, together with the correction of the free space gradient, we may obtain vertical precision of 1 cm. The use of mGal class precision absolute gravity instrument (such as FG5 type instrument shown in the drawing), it will provide even more reliable average seawater surface height as the base for national high precision height control system.


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