Netherlands (NLGEO2018)
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Authors: C. Slobbe, et al.
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Created: 2018
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Resp: B.A. Alberts
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Description:
NLGEO2018 is the quasi-geoid model for the Netherlands, including both the Dutch mainland and the Exclusive Economic Zone.
The area covered by the quasi-geoid is 50° < lat < 56°, 2° < lon < 8°, with a grid spacing of 0.0125°
(45") in latitude and 0.02° (72") in longitude. The NLGEO2018 quasi-geoid heights are referred to the ETRS89/GRS80 ellipsoid.
It is computed using radar altimetry data, terrestrial gravity anomalies, airborne gravity disturbances, and shipboard gravity anomalies.
The model is computed using the remove-compute-restore procedure. The long-wavelength signal content in the data is reduced by removing
the contribution of the GOCO05S global gravity field model complete to degree 280. At the very short wavelengths, residual terrain modelling
(RTM) is applied to the shipboard, terrestrial and airborne gravity datasets. The residual disturbing potential is parameterized over the target
area using Spherical Radial Basis Functions (SRBF). The SRBF coefficients and bias parameters for the sets of gravity anomalies and disturbances
are estimated using weighted least-squares with regularization, assuming white noise.
To support the exploitation of the NLGEO2018 gravimetric quasi-geoid for the conversion of GNSS derived heights to the NAP height system, several
post-processing steps were applied. First, as the NAP height system is a mean-tide height system (i.e., mean-tide crust = zero crust over
mean-tide geoid) the quasi-geoid was transformed from the zero-tide to the mean tide system. Thereafter, a corrector surface (also called
'innovation function') has been estimated from the differences between the geometric quasi-geoid at 82 GNSS/leveling points and the gravimetric
quasi-geoid. This surface also accounts for the difference between the fictitious datum point of the gravimetric NLGEO2018 and the datum point
of the NAP. Finally, the transformation from the tide-free permanent tide system adopted in the GNSS community and the mean-tide system
adopted in NAP, has been applied.
References:
C. Slobbe, R. Klees, H.H. Farahani, L. Huisman, B. Alberts, P. Voet, F. De Doncker (2019). The impact of noise in a GRACE/GOCE global
gravity model on a local quasi‐geoid. Journal of Geophysical Research: Solid Earth, 124(3), pp. 3219-3237.
DOI: 10.1029/2018JB016470
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