The Problem Of Ocean Tide In High Precision GPS Survey

With the development of the Global Positioning System (GPS) and the data processing methods,GPS has been widely used in various fields. The accuracy can reach to several millimeters in the crustal movement observation and the determination of zenith delay. Ocean tide has an effect on GPS stations and there is a strong correlation between the vertical displacement and the zenith delay at a GPS station,so the effect of ocean tide on the precise determination of GPS stations' coordinates,baseline vectors,and zenith delay should not be neglectable.Using CSR4.0 global ocean tide model and local ocean tide maps in China Seas,this paper calculated the ocean tidal displacement corrections caused by 11 ocean constitutes (Mb,S?,Na,K.2,KI,O|,PI,Q|,MI,Mm. Ssa) for the stations in the Crustal Movement Observation Network of China (CMONOC). This paper processed the GPS data ofCMONOC from 10th to 40th in 2001 with software GAMIT,and analy/ed the effects of ocean tide on baseline vectors and the determination of zenith delay.The result shows that the effects are about several centimeters for GPS stations and several millimeters for baseline vectors and the determination of zenith delay in maximum. In addition,the effects are periodical obviously and the effects on coastal stations are bigger than the effects on inland stations. We found that the averages of all the effects in a month are very little after calculation. This means the effects can be reduced by long-term continuous observation. But for the short-time observation,for example,the determination of zenith delay,the effects can't be reduced obviously,because the interval between the zenith delay parameters is often short.In a word,in the high precision GPS survey,the effect of ocean tide can't be neglectable,and the ocean tide corrections should be added and the local ocean tide maps in China Seas should be considered.