The KTH geoid based on Least Squares modification of Stokes integral with additive corrections for the Colorado Experiment: ColLSMSA-KTH2019

The ColLSMSA-KTH2019 gravimetric geoid model has been computed by the University of Gävle, the Lantmäteriet and the Royal Institute of Technology (KTH) in Sweden. The model has been worked out in the frame of the International Association of Geodesy Joint Working Group 2.2.2 "The 1 cm geoid experiment" and the so called "Colorado experiment". The area covered by the model is 251°E ≤ longitude ≤ 257°E, 36°N ≤ latitude ≤ 39°N with a grid spacing of 1' in both latitude and in longitude. The quasi-geoid is computed using a two-step procedure. First, the terrestrial and de-biased airborne gravity anomalies are gridded using a Remove-Compute-Restore technique and three-dimensional Least Squares Collocation (LSC) with spherical Tscherning and Rapp (1974) type of covariance functions. This step achieves downward continuation of the airborne gravity data and combination with the terrestrial observations. In the second step, the resulting surface gravity anomaly grid is used to compute height anomalies by using Least Squares Modification of Stokes’ formula with Additive corrections (LSMSA or KTH method). The GEOID17RefB global gravity model up to degree 2190 is used in the first gridding step, while the satellite-only GOCO05S model up to degree 240 is used in the second step. Finally, the classical formula by Heiskanen and Moritz (1967) is used for quasi-geoid to geoid conversion. The accuracy of the geoid model, when compared against GSVS17 GPS/leveling, is equal to 2.7 cm. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

ColLSMSA-KTH2019重力大地水准面模型（gravimetric geoid model）由瑞典耶夫勒大学、瑞典土地测绘局（Lantmäteriet）以及瑞典皇家理工学院（Royal Institute of Technology，KTH）联合研制。该模型的研制依托国际大地测量协会联合工作组2.2.2"1厘米大地水准面实验"以及所谓的"科罗拉多实验"框架开展。
该模型覆盖区域为东经251°≤经度≤257°、北纬36°≤纬度≤39°，经纬向网格间距均为1角分。
似大地水准面（quasi-geoid）的解算采用两步法流程：第一步，利用移除-计算-恢复（Remove-Compute-Restore）技术，以及采用球谐型Tscherning-Rapp（1974）协方差函数的三维最小二乘配置（Least Squares Collocation，简称LSC），对地面观测数据与经偏差校正的航空重力异常进行网格化处理。该步骤可实现航空重力数据的向下延拓，并与地面观测数据完成融合。
第二步，利用生成的地面重力异常网格，结合带附加改正的斯托克斯公式最小二乘修正法（Least Squares Modification of Stokes’ formula with Additive corrections，简称LSMSA，亦称KTH方法）解算高程异常。第一步网格化处理中，采用了截断阶数达2190的全球重力模型GEOID17RefB；第二步则采用了仅基于卫星数据、截断阶数为240的GOCO05S模型。
最后，借助Heiskanen与Moritz于1967年提出的经典公式完成似大地水准面至大地水准面的转换。与GSVS17 GPS/水准比对数据相较，该大地水准面模型的精度可达2.7厘米。
该大地水准面模型以ISG格式2.0版本（ISG Format Specifications）提供，其原始数据格式文件可于对应ISG模型网页获取。