The aim of this study is to determine an accurate geoid model for Iran based on the Least Squares Collocation method in the framework of the Remove — Compute — Restore technique. In areas suffering from a lack of homogeneous and accurate gravity anomaly data, as is the case of Iran, the choice of the most compatible global gravity model has a significant impact on the estimated form of the geoid. Different combined and satellite-only global gravity models were therefore analyzed for Iran, and EIGEN6C4 was selected as the best one. The Shuttle Radar Topography Mission height model was used for the residual terrain correction. The covariance modeling, a crucial step in the Least Squares Collocation method, was based on two strategies. In the first, the study area was divided into four sub-areas, and then an individual empirical covariance was computed and a covariance model fitted to each of them. In the second, an empirical covariance was computed using all terrestrial gravity data, and a unique covariance model was fitted to it. Despite some border effects, the former strategy showed slightly better performance according to the resulting statistics, and therefore it was preferred for the estimation of the geoid model called IRG2018. To remove the offset of IRG2018 with respect to GNSS/Leveling-derived geoid heights, two alternative approaches were tested: subtracting a fitting polynomial surface or directly using the GNSS/Leveling data as an input to the IRG2018 computation process. Evaluation of the results, based on an independent control set of approximately half of available GNSS/Leveling points, showed an advantage of the latter approach, with an estimated accuracy of about 20 cm in terms of RMS.

中文翻译：

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IRG2018：使用最小二乘搭配的伊朗区域大地水准面模型

这项研究的目的是在“删除—计算—恢复”技术的框架下，基于最小二乘配置方法，为伊朗确定一个准确的大地水准面模型。在缺乏均匀和准确的重力异常数据的地区，例如伊朗，最兼容的全球重力模型的选择对大地水准面的估计形式有重大影响。因此，针对伊朗分析了不同的组合式和仅卫星式全球重力模型，而EIGEN6C4被选为最佳模型。航天飞机雷达地形任务高度模型用于残余地形校正。协方差建模是最小二乘配置方法中的关键步骤，它基于两种策略。首先，研究区域分为四个子区域，然后计算一个个体经验协方差，并为每个模型拟合一个协方差模型。第二，使用所有地面重力数据计算经验协方差，并为其拟合唯一的协方差模型。尽管有一些边界影响，但根据所得统计数据，前一种策略仍显示出稍好一些的性能，因此对于估算称为IRG2018的大地水准面模型而言，它是首选。为了消除相对于GNSS /水准仪得出的大地水准面高度的IRG2018偏移，测试了两种替代方法：减去拟合的多项式曲面或直接使用GNSS /水准仪数据作为IRG2018计算过程的输入。根据大约GNSS /水准测量点的一半的独立控制集评估结果，