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Global Navigation Satellite System (GNSS) reflectometry is a promising technology used to estimate soil moisture, sea surface height, ice properties, etc. Interference signal technique is an important method to estimate these geophysical parameters. The effect of this method is closely related to the terrain and the receiving antenna placement. This study aims to investigate the effects of terrain and antenna placement on height measurement through simulation and field experiments. In this paper, we first simulated the interference signal in different types of terrain by parabolic equation method and analyzed the influence of terrain on the height measurement. Then we conducted three typical field experiments and processed experimental data. The simulated and experimental results indicate that the interference signal is affected by the terrain and the receiving antenna placement. Height measurement result is correct by both horizontal-looking and zenith-looking antenna when the ground is flat. However when the ground is not flat, the soil block near the receiving antenna leads to estimation errors. A more accurate estimation is obtained by using zenith-looking antenna to suppress the influence from the near terrain than horizontal-looking antenna. When a slope is near the receiving antenna, the signal with a high elevation may achieve an obvious interference effect if high elevation minus slope is equivalent to a low elevation. In this situation, the measurement height is the distance between the antenna and slope surface.

THE INFLUENCE OF THE TERRAIN ON HEIGHT MEASUREMENT USING THE GNSS INTERFERENCE SIGNAL