ABSTRACT
With the development of technology, GPS has been widely used in various types of construction engineering measurement. For general short baselines, tropospheric delay is highly correlated and can be eliminated by double-difference (Li and Huang, 2005). However, in hydraulic engineering, elevation difference between the two ends of the baseline is usually large, so is the meteorological differences. This may cause that the tropospheric delay cannot be eliminated effectively by double-difference or cause the failure of integer ambiguty operation even when the baselines are short (Ding, 2009). Researches have shown that when the satellite’s elevation is 20◦, relative tropospheric delay of 1 mm will lead to elevation error of 3 mm (Dai, 2011), which becomes the main constraint of GPS elevation accuracy. This short baseline and large elevation difference situation sometimes may be hard to avoid especially in dams, buildings and bridges, therefore the study of meteorological parameters in tropospheric delay correction is particularly important. In this paper, the effects of elevation difference on GPS monitoring results will be analyzed and some useful conclusions will be given.
