Evaluation of the Recent GOCE-based Global Geopotential Models in North America

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) dedicated satellite gravity field mission was launched on March 17, 2009. The GOCE came to an end in October 21, 2013. Five generations of global geopotential models (GGMs) have been computed and released based on the data collected by GOCE so far. The models are available via IAG's International Centre for Global Earth Models (ICGEM, http://icgem.gfz-potsdam.de/ICGEM/). The first generation models were computed from the first two months of the data, but the final generation models have been recently computed based on approximately 42 months of GOCE observations. Evaluation of these models in North America is important in view of the availability of high quality geodetic data in Canada and USA and the upcoming redefinition of the North American vertical datum through a continental geoid model based on a GOCE GGM. In this study, the performance of the models, developed by ESA's High-level Processing Facility (HPF), is evaluated by degree variances and also by comparing to the GNSS-levelling geoid undulations as independent control values. The GNSS-leveling stations in Canada, USA, Alaska and Mexico are used in this study. The results provide evidence that the signal of the Earth's gravitational field has been obtained solely from GOCE measurements up to degree and order (DO) 220, which corresponds to the spatial resolution of approximately 91 km. The cumulative global geoid error of TIM5 and DIR5 models up to DO 220 are 3.6 and 1.2 cm, respectively. The evaluation of the models by the North American GNSS-leveling stations in different spectral bands showed that the TIM5 and DIR5 models have slightly better performance than the EGM2008 model in the spectral band between DO 100 and 210 in Canada and the USA. The improvement brought by GOCE to Alaska and Mexico is more significant. In Alaska, the TIM5 and DIR5 models improve the geoid signal in the spectral band between DO 100 and 250. In Mexico, where good terrestrial gravity information is not available, the last generation of GOCE models improves the geoid signal between DO 110 and 280. The DIR models slightly perform better that the TIM models in North America. Standard deviations of the geoid height differences for the DIR5 model up to DO 300 are 25.5, 26.6, 35.7 and 49.0 cm in Canada, USA, Alaska and Mexico, respectively.