17:15 〜 17:30
[G02-6-04] Height datum unification by patching local geoid models
National geoid models are frequently used in engineering applications to transform GNSS derived ellipsoidal heights into orthometric heights. The establishment of a unique International Height Reference System (IHRS) among neighboring countries requires the verification of the consistency between national geoids. The choice of different reference tide gauges, reference frames and ellipsoids causes biases and in general systematic effects making local geoid models inconsistent to each other. These effects can be estimated and removed by exploiting modern satellite-only models.
In the present work, a unification strategy is presented, firstly estimating biases and systematic effects by a least-squares adjustment of the local geoid residuals with respect to a satellite-only model, and then correcting the remaining geoid distortions along the national borders by collocation. The advantage is that the resulting unified geoid includes both the low frequencies of the satellite-only global model and the high frequencies of the local ones. These high frequencies are expected to be more accurate in the definition of the equipotential than those coming from a "terrestrial" global geopotential model combined with the residual terrain effect. Moreover, this procedure allows for a fast update of the unified model when a new geoid is available.
The local models to be used as test data come from the archive of the International Service for the Geoid (ISG) and the result is compared with existing global and continental geoid models. It is expected that, if the used gravity data were not preliminarily reduced by biases, these models are more affected by distortions due to the different national reference systems.
This study is performed in the frame of the Joint Working Group 2.2.1 "Integration and validation of local geoid estimates" of IAG Commission 2 . The output will represent a new product of ISG and aims to be a contribution in the frame of GGOS for the establishment of an IHRS.
In the present work, a unification strategy is presented, firstly estimating biases and systematic effects by a least-squares adjustment of the local geoid residuals with respect to a satellite-only model, and then correcting the remaining geoid distortions along the national borders by collocation. The advantage is that the resulting unified geoid includes both the low frequencies of the satellite-only global model and the high frequencies of the local ones. These high frequencies are expected to be more accurate in the definition of the equipotential than those coming from a "terrestrial" global geopotential model combined with the residual terrain effect. Moreover, this procedure allows for a fast update of the unified model when a new geoid is available.
The local models to be used as test data come from the archive of the International Service for the Geoid (ISG) and the result is compared with existing global and continental geoid models. It is expected that, if the used gravity data were not preliminarily reduced by biases, these models are more affected by distortions due to the different national reference systems.
This study is performed in the frame of the Joint Working Group 2.2.1 "Integration and validation of local geoid estimates" of IAG Commission 2 . The output will represent a new product of ISG and aims to be a contribution in the frame of GGOS for the establishment of an IHRS.