The Mexican gravimetric geoid: GGM06

GGM06 is a gravimetric geoid model for Mexico calculated from a smaller but more reliable database of terrestrial gravimetry than the one used for its predecessor GGM05. The changes in geoidal height are mainly visible for the north-central territory of Mexico. The reference ellipsoid is GRS80, datum ITRF92 (epoch 1988.0). The input terrestrial gravity data consisted of nearly 30,000 points inside Mexico obtained from INEGI and US-DMA. Marine gravity was derived from Topex/Poseidon altimetry. The used digital terrain models were CEM1 and SRTM. A reference satellite geoid model was also used up to degree and order 40 from the GRACE geopotential model GGM02. The computation methodology was based on the Stokes-Helmert technique with the software provided by the University of New Brunswick (UNB), similar to the previous computation GGM05, but with an improved methodology for gravity data cleaning. The resulting GGM06 model is referred to the GRS80 reference ellipsoid in the ITRF92 frame (epoch 1988.0). The error RMS of geoidal heights is 35 cm, estimated from 1384 GPS/leveling data points. 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.

GGM06是一款面向墨西哥的重力大地水准面模型（gravimetric geoid model），相较于其前代模型GGM05，其解算所依托的地面重力测量数据库规模更小但可靠性更高。大地水准面高的变化特征主要在墨西哥中北部区域显现。该模型采用GRS80参考椭球，基准为ITRF92（历元1988.0）。输入的地面重力数据涵盖取自INEGI与US-DMA的墨西哥境内近3万个测点。海洋重力数据由Topex/Poseidon测高数据反演获取。所用数字地形模型为CEM1与SRTM。此外还采用了基于GRACE地球重力场模型GGM02解算的、阶次至40的参考卫星大地水准面模型。本次解算基于斯托克斯-赫姆特（Stokes-Helmert）技术，采用新不伦瑞克大学（University of New Brunswick, UNB）提供的软件，解算流程与前代模型GGM05类似，但针对重力数据清洗环节优化了解算方法。最终得到的GGM06模型基于ITRF92坐标系下的GRS80参考椭球（历元1988.0）。通过1384组GPS/水准测点估算，该模型的大地水准面高误差均方根（Root Mean Square, RMS）为35厘米。该大地水准面模型以ISG格式2.0（ISG格式规范）提供，其原始数据格式文件可在该模型的ISG官方网页获取。