Determining Deflection of the Vertical with GPS

In classic Geodesy, deflection of the vertical is defined by the astro-geodetic technique. Precise astronomical coordinates determination need a well trained surveyor, and in addition, t.hey are expensive. These limitations have to be considered when planning a geodetic project in which deflection of the vertical needs to be determined. In the era of GPS, The deflection can be obtained by calculating the differences between the astronomical and geodetic zenith angle. Instead of dealing with astronomical and geodetic coordinates difference, one may deal with zenith angles difference. Moreover, the method seems to be much more economical than the classic one and is easy to implement. Test experiments have shown that it is possible to obtain accurate results as by the astro-geodetic technique after only a few hours of field operation. The option of accurate, fast and economic determination of the deflection may be used for precise geoid determination. This topic is not included in the paper and should be carefully'investigated.