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A new technique to determine geoid and orthometric heights from satellite positioning and geopotential numbers 总被引:1,自引:0,他引:1
L. E. Sjöberg 《Journal of Geodesy》2006,80(6):304-312
This paper takes advantage of space-technique-derived positions on the Earth’s surface and the known normal gravity field to determine the height anomaly from geopotential numbers. A new method is also presented to downward-continue the height anomaly to the geoid height. The orthometric height is determined as the difference between the geodetic (ellipsoidal) height derived by space-geodetic techniques and the geoid height. It is shown that, due to the very high correlation between the geodetic height and the computed geoid height, the error of the orthometric height determined by this method is usually much smaller than that provided by standard GPS/levelling. Also included is a practical formula to correct the Helmert orthometric height by adding two correction terms: a topographic roughness term and a correction term for lateral topographic mass–density variations. 相似文献
144.
M. C. Santos P. Vaníček W. E. Featherstone R. Kingdon A. Ellmann B. -A. Martin M. Kuhn R. Tenzer 《Journal of Geodesy》2006,80(12):691-704
Following our earlier definition of the rigorous orthometric height [J Geod 79(1-3):82–92 (2005)] we present the derivation and calculation of the differences between this and the Helmert orthometric height, which is embedded in the vertical datums used in numerous countries. By way of comparison, we also consider Mader and Niethammer’s refinements to the Helmert orthometric height. For a profile across the Canadian Rocky Mountains (maximum height of ~2,800 m), the rigorous correction to Helmert’s height reaches ~13 cm, whereas the Mader and Niethammer corrections only reach ~3 cm. The discrepancy is due mostly to the rigorous correction’s consideration of the geoid-generated gravity disturbance. We also point out that several of the terms derived here are the same as those used in regional gravimetric geoid models, thus simplifying their implementation. This will enable those who currently use Helmert orthometric heights to upgrade them to a more rigorous height system based on the Earth’s gravity field and one that is more compatible with a regional geoid model. 相似文献
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Explicit formula for the geoid-quasigeoid separation 总被引:1,自引:0,他引:1
The explicit formula for the geoid-to-quasigeoid correction is derived in this paper. On comparing the geoidal height and
height anomaly, this correction is found to be a function of the mean value of gravity disturbance along the plumbline within
the topography. To evaluate the mean gravity disturbance, the gravity field of the Earth is decomposed into components generated
by masses within the geoid, topography and atmosphere. Newton’s integration is then used for the computation of topography-and
atmosphere-generated components of the mean gravity, while the combined solution for the downward continuation of gravity
anomalies and Stokes’ boundary-value problem is utilized in computing the component of mean gravity disturbance generated
by mass irregularities within the geoid. On application of this explicit formulism a theoretical accuracy of a few millimetres
can be achieved in evaluation of the geoid-to-quasigeoid correction. However, the real accuracy could be lower due to deficiencies
within the numerical methods and to errors within the input data (digital terrain and density models and gravity observations). 相似文献
147.
Juan Carlos Bergmann 《Boundary-Layer Meteorology》2006,119(1):171-179
Precision measurements indicate that the stability capping of the neutral planetary boundary layer (PBL) that leads to a reduced
PBL height is caused by the very stable upper part of the PBL, rather than by an overlying inversion. Radiative processes
related to liquid water in boundary-layer clouds seem to play the key role for the formation of the stable upper PBL. The
famous Leipzig Profile – generally considered as an example of a neutral PBL – has been included in Hess’s analysis because
its PBL height is considerably lower than the ca. 3000 m to be expected by numerical models in truly neutral conditions. An
analysis of the original observations reveals that the Leipzig PBL was stable and that it can be consistently treated as a
‘normal’ stable PBL with a height of ca. 700 m. A further finding is that the super-geostrophic PBL wind speed maxima predicted
by almost all models are not observed in near-steady-state conditions. For the ‘ranking’ of analytical models versus numerical
models, the comparisons with measurements show that the analytical models perform comparably well and even partially better
than the numerical models. 相似文献
148.
A. A. M. Holtslag G. J. Steeneveld B. J. H. van de Wiel 《Boundary-Layer Meteorology》2007,125(2):361-376
At present a variety of boundary-layer schemes is in use in numerical models and often a large variation of model results
is found. This is clear from model intercomparisons, such as organized within the GEWEX Atmospheric Boundary Layer Study (GABLS).
In this paper we analyze how the specification of the land-surface temperature affects the results of a boundary-layer scheme,
in particular for stable conditions. As such we use a well established column model of the boundary layer and we vary relevant
parameters in the turbulence scheme for stable conditions. By doing so, we can reproduce the outcome for a variety of boundary-layer
models. This is illustrated with the original set-up of the second GABLS intercomparison study using prescribed geostrophic
winds and land-surface temperatures as inspired by (but not identical to) observations of CASES-99 for a period of more than
two diurnal cycles. The model runs are repeated using a surface temperature that is calculated with a simple land-surface
scheme. In the latter case, it is found that the range of model results in stable conditions is reduced for the sensible heat
fluxes, and the profiles of potential temperature and wind speed. However, in the latter case the modelled surface temperatures
are rather different than with the original set-up, which also impacts on near-surface air temperature and wind speed. As
such it appears that the model results in stable conditions are strongly influenced by non-linear feedbacks in which the magnitude
of the geostrophic wind speed and the related land-surface temperature play an important role. 相似文献
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