The multipath effect on carrier-phase observations is related to the observational environment of the station, and cannot be eliminated or attenuated by the differential method. In the actual dam environment of deformation monitoring, multipath is very complicated. It is the main error source of BDS-2 for high precision data processing. In this paper, a new method called the multi-point hemispherical grid model (MHGM) is studied and evaluated. This method uses the hemispheric grid model to attenuate the influence of multipath errors. The effectiveness and improvement of the new method with respect to the popular sidereal filter (SF) method were assessed and verified by the actual dam monitoring data with only the BDS-2. The MHGM and SF approach calculates the multipath corrections from multi-days historical data, and then corrects the multipath error from the observations on the day of interest. Compared with the SF method, the MHGM can also effectively provide a graphical display of multipath error interference around the stations, which matches the surrounding observation environment. The results show that the double-differenced (DD) residuals of the MHGM for GEO/IGSO and MEO satellites are slightly better than those of SF, but the RMS of MHGM for GEO/IGSO+MEO DD residuals is improved by about 17.0%. The performance of the MHGM method for different satellite constellations is consistent and not affected by the different orbital repeat times, which could solve the "zero mean" assumption problem of the SF method. Meanwhile, the RMS of static with a 2 hours interval and kinematic positioning errors of the MHGM method in the horizontal and vertical direction can be up to 1.7, 3.6 and 2.4, 8.1 mm, respectively. The MHGM model could avoid the multipath reference problem caused by different orbital repetition periods, making it more suitable for the combined multipath modeling of BDS-2 and BDS-3.

中文翻译：

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缓解BDS-2大坝变形监测多径误差的新方法

对载波相位观测的多径效应与台站的观测环境有关，不能通过差分方法消除或衰减。在实际的大坝变形监测环境中，多径非常复杂。它是用于高精度数据处理的BDS-2的主要错误源。本文研究并评估了一种称为多点半球网格模型（MHGM）的新方法。该方法使用半球网格模型来衰减多径误差的影响。通过仅使用BDS-2的实际大坝监测数据，可以评估和验证新方法相对于流行的恒星过滤器（SF）方法的有效性和改进。MHGM和SF方法可根据多天的历史数据计算出多径校正，然后在感兴趣的当天根据观测值校正多径误差。与SF方法相比，MHGM还可以有效地提供站周围多径误差干扰的图形显示，该图形显示与周围的观察环境相匹配。结果表明，GEO / IGSO和MEO卫星的MHGM的双差（DD）残差比SF稍好，但GEO / IGSO + MEO DD残差的MHGM的均方根值提高了约17.0％。MHGM方法在不同卫星星座上的性能是一致的，不受不同的轨道重复时间的影响，这可以解决SF方法的“零均值”假设问题。同时，间隔2小时的静态RMS值和MHGM方法在水平和垂直方向上的运动定位误差分别可以达到1.7、3.6和2.4、8.1 mm。MHGM模型可以避免由不同的轨道重复周期引起的多径参考问题，使其更适合BDS-2和BDS-3的组合多径建模。