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1.
2.
Lars E. Sjöberg 《Journal of Geodesy》2008,82(9):565-567
Through each of two known points on the ellipsoid a geodesic is passing in a known azimuth. We solve the problem of intersection
of the two geodesics. The solution for the latitude is obtained as a closed formula for the sphere plus a small correction,
of the order of the eccentricity of the ellipsoid, which is determined by numerical integration. The solution is iterative.
Once the latitude is obtained, the longitude is determined without iteration. 相似文献
3.
Assuming a radially stratified Newtonian mantle in a steady-state approximation, we demonstrate that the permeability of a viscosity interface at 660-km depth strongly depends on the wavelength of buoyancy forces driving the flow. The flow induced by long-wavelength loads penetrates through the boundary freely even if the viscosity increases by two orders. In contrast, the boundary is practically impermeable for short-wavelength loads located in the upper mantle. Thus, a stepwise increase of viscosity is a significant obstacle for small descending features in the upper mantle, but huge upper mantle downwellings, or upwellings formed in the-lower mantle can overcome it easily. This indicates that certain care is necessary in interpreting the seismic structure of the mantle by means of flow models. The global tomographic image includes only the first few degrees of the harmonic series and, consequently, its interpretation in terms of a present-day flow field results in a predominantly whole-mantle circulation even for extreme viscosity contrasts. 相似文献
4.
5.
Bo A. Sjöberg 《Studia Geophysica et Geodaetica》1994,38(4):359-374
Summary A magnetostratigraphic subdivision of the Danian and Upper Maastrichtian at Limhamn, souternmost Sweden, based upon 63 samples
from drill cores (only up and down is known), is proposed. The boundary between the Maastrichtian and the Danian — situated
in chron 29R — was determined by means of nanofossils. It is marked by a hardground surface indicating a hiatus with an estimated
duration of 100 ka. The presence of chron 28R at the top of the Limhamn rock sequence and chron 30R in the Maastrichtian is
indicated by single samples with reversed polarity. Net sedimentation rates have been calculated on the basis of the proposed
magnetochronozones. the highest net sedimentation rate is found in the Danian part of chron 29R. 相似文献
6.
7.
Temperature dependence of calcite dissolution kinetics between 1 and 62°C at pH 2.7 to 8.4 in aqueous solutions 总被引:1,自引:0,他引:1
The kinetics of calcite dissolution in aqueous KCl-solutions far from equilibrium, between 1 and 62°C in the pH-range 2.7 to 8.4 have been investigated using a rotating disc apparatus. At neutral and alkaline pH in the mixed kinetic regime the empirical apparent activation energy (EAAE) for the surface chemical reaction rate constant is 54 ± 4 kJ mole?1 for Carrara marble and 46 ± 4 kJ mole?1 for Iceland spar. Under similar conditions the EAAE of the transport rate constant increases with decreasing temperature, but has a mean value of 27 ± 2 kJ mole?1. The corresponding diffusion coefficient has a mean EAAE of 37 ± 3 kJ mole?1 and this high EAAE is consistent with transport dependence on product diffusion in this H+-independent regime.In contrast, in acid solutions, where the rate approaches end-member transport control, the EAAE of the diffusion coefficient is 16 kJ mole?1, also decreasing with increasing temperature. This is compatible with H+-diffusion to the surface being rate-controlling.In inhibitor-free natural systems, calcite dissolution kinetics far from equilibrium can be described in terms of three regimes: an H+-dependent regime (pH < 4 at 25°C), a transition regime (4 < pH < 5.5 at 25°C) and an H+-independent regime (pH > 5.5 at 25°C). At lower temperatures these boundaries move to higher pH values. The presence of inhibitors in natural systems may enhance surface controlled kinetics. 相似文献
8.
L. E. Sjöberg 《Journal of Geodesy》2001,75(5-6):283-290
The topographic and atmospheric effects of gravimetric geoid determination by the modified Stokes formula, which combines
terrestrial gravity and a global geopotential model, are presented. Special emphasis is given to the zero- and first-degree
effects. The normal potential is defined in the traditional way, such that the disturbing potential in the exterior of the
masses contains no zero- and first-degree harmonics. In contrast, it is shown that, as a result of the topographic masses,
the gravimetric geoid includes such harmonics of the order of several centimetres. In addition, the atmosphere contributes
with a zero-degree harmonic of magnitude within 1 cm.
Received: 5 November 1999 / Accepted: 22 January 2001 相似文献
9.
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
10.
L. E. Sjöberg 《Journal of Geodesy》2007,81(5):345-350
This study emphasizes that the harmonic downward continuation of an external representation of the Earth’s gravity potential
to sea level through the topographic masses implies a topographic bias. It is shown that the bias is only dependent on the
topographic density along the geocentric radius at the computation point. The bias corresponds to the combined topographic
geoid effect, i.e., the sum of the direct and indirect topographic effects. For a laterally variable topographic density function,
the combined geoid effect is proportional to terms of powers two and three of the topographic height, while all higher order
terms vanish. The result is useful in geoid determination by analytical continuation, e.g., from an Earth gravity model, Stokes’s
formula or a combination thereof. 相似文献