Geoid Research Articles

Oxygen in Ge crystals grown by the B2O3 encapsulated Czochralski method

Local vibrations of oxygen in Ge crystals grown by the Czochralski method adopting liquid-B2O3 encapsulation and GeO2 powder doping were investigated by Fourier-transform infrared spectroscopy. Strong absorption peaks at 855cm−1, originating in local vibration of interstitially dissolved oxygen Oi as Ge–Oi–Ge quasi-molecules, developed depending on the doped amount of GeO2. Similarly, an absorption peak related to the combined vibration of Ge–Oi–Ge was found at 1264cm−1 and the conversion factor from the peak intensity to the oxygen concentration was evaluated to be 1.15×1019cm−2. By prolonged annealing at 350°C an absorption peak developed at 780cm−1, indicating formation of oxygen-related thermal donors. From the variations of carrier density and oxygen concentration, one donor was found to possess about 15 Oi atoms.

Review and Prospect for the Earth Gravity Field Determination with Gravity Satellites in the Past Five Years

The technical behaviors and preliminary results in the global gravity field determination obtained from the gravity satellites CHAMP,GRACE and GOCE which will be launch in the near future,are reviewed,compared and summarized.The possible development for the construction of static and kinematic global gravity model based on the observation data of these gravity satellites are also given in the paper.A CHAMP only global gravity field model derived from 33 months of mission data is much better than GRIM5-S1,which was derived from the pre-CHAMP multi-satellite data.The resolution for the result derived from GRACE 110days data is better than that derived from CHAMP mission data mentioned above.There is another task for the GRACE mission,i.e.,to determine the real or near real time non tidal variation in the global gravity field.A new combined earth gravity model EIGEN-CG03C,360 order and degree,30' resolution is introduced in the paper.In comparison with the former earth gravity model the accuracy of CG03C is improved by one magnitude in the 400 m wave length,that of geoid is improved by 3 cm,and that of surface gravity anomaly is improved by 0.4 mgal.

Ab initio modeling of interstitial oxygen in crystalline SiGe alloys

We have investigated the structural and vibrational properties of interstitial oxygen in Si1−xGex alloys by using a pseudopotential density-functional code and 128 atom supercells. First, to test the method, well-established data for interstitial oxygen in Si and Ge were reproduced. Secondly, to model the alloys, Si atoms were randomly replaced by Ge atoms in an otherwise perfect 128 Si atom supercell. Atomic and volumetric degrees of freedom were allowed to relax. We found from energetics that interstitial oxygen prefers to bond with silicon atoms for a large range of Ge concentrations (x=25%, 50%, 75%). The defect model accounts well for the observed red-shift of the asymmetric stretch mode band when increasing the Ge concentration. On the other hand, highly energetic Ge–Oi–Si and Ge–Oi–Ge structures produce frequencies not seen experimentally. Therefore we conclude that oxygen only forms Si–Oi–Si units in crystalline SiGe alloys for a large range of Ge compositions.

The Elusive Stationary Geoid

The Elusive Stationary Geoid

To: “Ellipsoid, geoid, gravity, geodesy, and geophysics,” X. Li and H.-J. Götze (Geophysics, 66, 1660–1668).

To: “Ellipsoid, geoid, gravity, geodesy, and geophysics,” X. Li and H.-J. Götze (Geophysics, 66, 1660–1668).

PROGRESS OF DYNAMIC GEODESY IN CHINA

The achievements and international cooperation of studies in five aspects, such as earth tide and non tidal gravity, Earth polar displacement and variation of rotation rate, geoid and sea level change, plate movement and crustal deformation, movement of the matter within the earth's interior, by the theory, method and technique of geodesy, geophysics and astrometry in near four decades, especially the recent decade, is summered in the paper. Despite of late launch of the study on dynamic geodesy in China, the progress is fairly rapid. It plays a certain role in the eco environment and hazard prediction related to the national economy and people's livelihood, as well as takes a proper place in the domestic and international geoscience research. With the launch and implement of several projects, such as the “Plan of Geodynamics in Asian and Pacific Region”, National Climbing Project “Modern Crustal Movement and Geodynamics Research”, National Key Scientific Engineering Project “Observation Network of Crustal Movement in China”, studies on dynamic geodymics must be progressing rapidly.

3D-Convection in the moon and the influence on topography and geoid

3D-Convection in the moon and the influence on topography and geoid

On the combined adjustment of a gravimetrically determined geoid and GPS levelling stations

On the combined adjustment of a gravimetrically determined geoid and GPS levelling stations

Depth to basement and geoid expression of the Kane Fracture Zone: A comparison

Geoid data from Geosat and subsatellite basement depth profiles of the Kane Fracture Zone in the central North Atlantic were used to examine the correlation between the short-wavelength geoid (λ=25–100 km) and the uncompensated basement topography. The processing technique we apply allows the stacking of geoid profiles, although each repeat cycle has an unknown long-wavelength bias. We first formed the derivative of individual profiles, stacked up to 22 repeat cycles, and then integrated the average-slope profile to reconstruct the geoid height. The stacked, filtered geoid profiles have a noise level of about 7 mm in geoid height. The subsatellite basement topography was obtained from a recent compilation of structure contours on basement along the entire length of the Kane Fracture Zone. The ratio of geoid height to topography over the Kane Fracture Zone valley decreases from about 20–25 cm km-1 over young ocean crust to 5–0 cm km-1 over ocean crust older than 140 Ma. Both geoid and basement depth of profiles were projected perpendicular to the Kane Fracture Zone, resampled at equal intervals and then cross correlated. The cross correlation shows that the short-wavelength geoid height is well correlated with the basement topography. For 33 of the 37 examined pro-files, the horizontal mismatches are 10 km or less with an average mismatch of about 5 km. This correlation is quite good considering that the average width of the Kane Fracture Zone valley at median depth is 10–15 km. The remaining four profiles either cross the transverse ridge just east of the active Kane transform zone or overlie old crust of the M-anomaly sequence. The mismatch over the transverse ridge probably is related to a crustal density anomaly. The relatively poor correlation of geoid and basement depth in profiles of ocean crust older than 130–140 Ma reflects poor basement-depth control along subsatellite tracks.

The geoid and geodynamics

The geoid and geodynamics

An investigation of the geoid in Europe

An investigation of the geoid in Europe

On the geoid study of the International Isostatic Institute

On the geoid study of the International Isostatic Institute

Formation of Ellipsoidal Geoid

Formation of Ellipsoidal Geoid

Construction of the Geoid

Construction of the Geoid