A lake height variation measurement method utilizing global navigation satellite system(GNSS) reflected signal carrier phase was given. Carrier phase observation equations were built firstly. Then the single-differences between the carrier phase observation measurements for direct and reflected signal and the double-differences between epochs were calculated. A large amount of errors was eliminated by the differencing process. Also, the geometry path differences of direct and reflected signal were derived. The lake height variation was calculated using observation measurement and elevation information from separate satellite. The weighted average of the lake height variations from various satellites was derived to improve the precision and reliability of the measuring system. Simulation confirms that the precision of millimeter order is achieved with the method under -15�bdB signal to noise ratio(SNR).
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