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Stefan Maus Chris M. Green & J. Derek Fairhead 《Geophysical Journal International》1998,134(1):243-253
The ocean geoid can be inferred from the topography of the mean sea surface. Satellite altimeters transmit radar pulses and determine the return traveltime to measure sea-surface height. The ERS-1 altimeter stacks 51 consecutive radar reflections on board the satellite to a single waveform. Tracking the time shift of the waveform gives an estimate of the distance to the sea surface. We retrack the ERS-1 radar traveltimes using a model that is focused on the leading edge of the waveforms. While earlier methods regarded adjacent waveforms as independent statistical events, we invert a whole sequence of waveforms simultaneously for a spline geoid solution. Smoothness is controlled by spectral constraints on the spline coefficients. Our geoid solutions have an average spectral density equal to the expected power spectrum of the true geoid. The coherence of repeat track solutions indicates a spatial resolution of 31 km, as compared to 41 km resolution for the ERS-1 Ocean Product. While the resolution of the latter deteriorates to 47 km for wave heights above 2 m, our geoid solution maintains its resolution of 31 km for rough sea. Retracking altimeter waveform data and constraining the solution by a spectral model leads to a realistic geoid solution with significantly improved along-track resolution. 相似文献
64.
Derek York 《Earth and Planetary Science Letters》1978,39(1):89-93
The following new theorem is proved: the equation E/RTB =ln(1.781 k0τ), where E = activation energy, R = the molar gas constant and TB = blocking temperature, applies equally well to both the isotopic and the magnetic systems in rocks from a cooling orogen. The isotopic model involves first-order loss of daughter, while the magnetic model applies to an assemblage of single-domain grains with constant E. Dodson supplied the original proof that the equation applied to isotopic systems. The well-known superficial similarity between the concepts of isotopic and magnetic blocking is thus given quantitative expression. 相似文献
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Derek R. Diamond 《Geoforum》1979,10(3):275-282
Failure to fully understand or recognise crucial but culturally-determined British dimensions has led to confusion and error even among the British geographers in understanding and contributing to, urban and regional planning. This point assumes more rather than less significance in the context of a discussion between British and Soviet geographers. This paper therefore examines in part one, three fundamental features of the British system of urban and regional planning and then proceeds in part two to focus on the aims and their implementation. It concludes with a reference to the nature of the relationship between planning and geography. 相似文献
66.
Computations of concentrations of minor stratospheric gases using a two-dimensional model of the stratosphere are reported. The model includes Rayleigh scattering. This results in an increase in the photodissociation rate computation time by a factor of 1.5. The effect of ground albedo is assessed by comparing our results with a calculation of photolysis rates for a constant albedo with latitude. Comparison of results with a reference model including only molecular absorption are also made. The largest differences (50%) occur in NO and OH. An approximate expression for including the effects of Rayleigh scattering and surface reflectance in multi-dimensional models is suggested. 相似文献
67.
Henry P Schwarcz Russell S Harmon Peter Thompson Derek C Ford 《Geochimica et cosmochimica acta》1976,40(6):657-665
Fluid inclusions found trapped in speleothems (cave deposited travertine) are interpreted as samples of seepage water from which enclosing calcium carbonate was deposited. The inclusions are assumed to have preserved their D/H ratios since the time of deposition. Initial 18O/16O ratios can be inferred from δD because rain- and snow-derived seepage waters fall on the meteoric water line (δD = 8δ18O + 10). Estimates of temperature of deposition of the carbonate can be calculated from inclusion D/H ratios and δ18O of enclosing calcite in Pleistocene speleothems. For most speleothems investigated (0–200,000 yr old) δ18O of calcite appears to have decreased with increasing temperature of deposition indicating that the dominant cause of climate-dependent change in δ18O of calcite was the change in Kcw, the isotope fractionation equilibrium constant, with temperature; δ18O of meteoric precipitation generally increased with increasing temperature, but not sufficiently to compensate for the decrease in Kcw. 相似文献
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