Performance comparison of semicodeless GPS receivers for LEO satellites   总被引：1，自引：0，他引：1  

Oliver Montenbruck  Miquel Garcia-Fernandez  Jacob Williams 《GPS Solutions》2006,10(4):249-261

This report provides a detailed performance analysis of three semicodeless dual-frequency GPS receivers for use in low Earth orbit (LEO). The test set comprises the IGOR receiver, which represents a follow-on of the flight-proven BlackJack receiver, as well as two geodetic receivers (NovAtel OEM4-G2 and Septentrio PolaRx2), which are entirely based on commercial-off-the-shelf technology (COTS). All three receivers are considered for upcoming flight projects or experiments and have undergone at least a preliminary environmental qualification program. Using extensive signal simulator tests, the cold start signal acquisition, tracking sensitivity, differential code biases, raw measurement accuracy, and navigation accuracy of each receiver have been assessed. All tests are based on a common scenario that is representative of an actual space mission and provides a realistic simulation of the signal dynamics and quality on a scientific LEO satellite. Compared to the other receivers, the IGOR instrument exhibits a superior tracking sensitivity and is thus best suited for occultation measurements with low tangent point altitudes. The OEM4-G2 and PolaRx2 receivers are likewise shown to properly track dual-frequency GPS signals and normal signal levels and to provide accurate code and carrier phase measurements. Given their limited resource requirements, these receivers appear well suited for precise orbit determination applications and ionospheric sounding onboard of microsatellites with tight mission budgets.  相似文献   

A wide-angle seismic traverse through the Variscan of southwest Ireland     

F. Masson  A. W. B. Jacob  C. Prodehl  P. W. Readman  P. M. Shannon  A. Schulze  & U. Enderle 《Geophysical Journal International》1998,134(3):689-705

A wide-angle seismic profile across the western peninsulas of SW Ireland was performed. This region corresponds to the northernmost Variscan thrust and fold deformation. The dense set of 13 shots and 109 stations along the 120  km long profile provides a detailed velocity model of the crust.
  The seismic velocity model, obtained by forward and inverse modelling, defines a five-layer crust. A sedimentary layer, 5–8  km thick, is underlain by an upper-crustal layer of variable thickness, with a base generally at a depth of 10–12  km. Two mid-crustal layers are defined, and a lower-crustal layer below 22  km. The Moho lies at a depth of 30–32  km. A low-velocity zone, which coincides with a well-defined gravity low, is observed in the central part of the region and is modelled as a Caledonian granite which intruded upper-crustal basement. The granite may have acted as a buffer to northward-directed Variscan thrusting. The Dingle–Dungarvan Line (DDL) marks a major change in sedimentary and crustal velocity and structure. It lies immediately to the north of the velocity and gravity low, and shows thickness and velocity differences in many of the underlying crustal layers and even in the Moho. This suggests a deep, pre-Variscan control of the structural development of this area. The model is compatible with thin-skinned tectonics, which terminated at the DDL and which incorporated thrusts involving the sedimentary and upper-crustal layers.  相似文献   

Self-organization of recent rhythmic iron-manganese precipitations in underground mines in the Harz mountains     

S. Dietrich  K. -H. Jacob 《International Journal of Earth Sciences》1996,85(1):29-37

A recent early diagenetic banded iron-manganese mud has been forming underground in a closed lead-zinc mine for approximately 40 years. The processes leading to the banded structure of the precipitate were studied during a period of 2 years. Therefore, 19 physical and chemical parameters were measured regularly in short intervals. The resulting time series were analysed with respect to the data sets of the monthly chemical analyses of the descendent mine water, the daily rainfall and the mineral content. The results reveal that the precipitated material undergoes internal self-organization due to interaction of redox, colloid-chemical, microbial, electrical and ripening processes, and not exclusively produced by seasonal fluctuations of material input. Thus, the primary banding of the material, caused by externally forced fluctuations of the redox conditions within the mine water, is reorganized after a short time. The finally observed bands are controlled by non-linear coupling of reaction and transport processes within the mud. A genetic model for the banded mineralization was developed and verified by numerical simulation.  相似文献   

Sensitivity studies with the regional climate model REMO   总被引：14，自引：0，他引：14  

Dr. D. Jacob  R. Podzun 《Meteorology and Atmospheric Physics》1997,63(1-2):119-129

Summary A new regional atmospheric model was set up in a joint effort by DKRZ (Deutsches Klimarechenzentrum), DWD (Deutscher Wetterdienst), GKSS (Forschungszentrum Geesthacht) at the MPI (Max-Planck-Institut fuer Meteorologie). This model, called REMO (REgional MOdel) can be used in the weather forecast mode as well as in the climate mode. It is based on the Europa-Model (EM), the main weather forecast model of the new numerical weather prediction system of the Deutscher Wetterdienst. In addition to the physical parameterizations implemented in the EM, REMO has the possibility of using the same physics as the global climate model (MPI) into which it is nested to assess the scale dependence of physical parameterizations within the same dynamical framework.This paper gives an overview over different case studies investigating the dependence of model results on simulation domain size, horizontal resolution, initial conditions and lateral boundaries especially for long term calculations. A sample of one month long integrations for an arbitrary July month, a four year long run for the Baltic Sea and its drainage basin and two summer seasons of the Indian Monsoon will be used to demonstrate the sensitivity of regional climate model results to different environments.The sensitivity studies show that it is very important to use realistic large scale driving fields at the lateral boundaries. The regional model results are strongly influenced by the driving fields. The domain size and the simulation length are also influencing the results.With 12 Figures  相似文献   

Continental crust under the southern Porcupine Seabight west of Ireland     

J. Makris  R. Egloff  A.W.B. Jacob  P. Mohr  T. Murphy  P. Ryan 《Earth and Planetary Science Letters》1988,89(3-4)

Two new seismic refraction/wide-angle reflection profiles demonstrate that the crust beneath the southern Porcupine Seabight, out to water depths in excess of 4000 m, is of continental type. They also reveal the rifted margin of the Porcupine basin on its eastern side. Crustal thickness under the Seabight, inclusive of sediments which are up to 6 km thick, decreases from 23 km in the east to about 10 km at a sharp continent-ocean transition in the west.  相似文献   

Boundary-layer pollutant concentrations over complex terrain     

Jacob Padro 《Boundary-Layer Meteorology》1987,38(1-2):17-28

Given the incident profiles of wind velocity and pollutant concentration, we seek to determine the 3-dimensional concentration field of a pollutant upon a region with complex terrain. The analytic solution of the wind velocity in a 3-dimensional boundary-layer model by Walmsley et al. (1980) is utilized as a forcing function in the simplified concentration perturbation equation for a pollutant. The resulting solution applies to an isolated cosine-squared hill in a neutrally stratified boundary-layer flow with a surface type which absorbs the pollutant totally. The solution shows that the concentration perturbation field is organized in accordance with the wind field. In particular, the east-west cross-section is 180° out of phase with the velocity perturbation field. The vertical profiles of the concentration perturbations for selected grid points approach the value of the upper boundary condition very rapidly.  相似文献   

Modeling of centrifugal filtration in unsaturated deformable porous media     

Jacob Bear 《Advances in water resources》1984,7(4):150-167

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The occurrence and distribution of Mo and molybdenite in unaltered peralkaline rhyolites from Pantelleria,Italy   总被引：4，自引：0，他引：4  

Jacob B. Lowenstern  Gail A. Mahood  Richard L. Hervig  Joel Sparks 《Contributions to Mineralogy and Petrology》1993,114(1):119-129

Small hexagonal and triangular platelets of molybdenite (MoS₂), 5 to 25 m in diameter, were identified in phenocrysts and matrix glass of unaltered felsic volcanic rocks from Pantelleria, Italy. The MoS₂ occurs commonly in pantellerites (peralkaline rhyolites), rarely in pantelleritic trachytes, and never in trachytes. The occurrence of euhedral MoS₂ platelets in all phenocryst phases, in matrix glass, and even in some melt inclusions indicates that MoS₂ precipitated directly from the peralkaline melt. Despite MoS₂ saturation, the melt (glass) contains greater than 95% of the Mo in Pantellerian rocks: X-ray fluorescence analyses of 20 whole rocks and separated glasses show that whole rocks consistently contain less Mo than corresponding matrix glasses, the differences being in proportion to phenocryst abundances. The Mo contents increase with differentiation from trachytes (2–12 ppm) to pantellerites (15–25 ppm) and correlate positively with incompatible elements such as Th, Y, and Nb. The Mo concentrations, as determined by secondary ion mass spectrometry, are essentially the same in matrix glasses and melt inclusions, showing that Mo did not partition strongly into a volatile fluid phase during outgassing. The high Mo contents of the pantellerites (relative to metaluminous magmas with 1–5 ppm) may be due to several factors: (1) the enhanced stability of highly charged cations (such as Mo⁶⁺, U⁴⁺, and Zr⁴⁺) in peralkaline melts; (2) the rarity of Fe-Ti oxides and litanite into which Mo might normally partition; (3) reduced volatility of Mo in low fO₂, H₂O-poor (1–2 wt%) peralkaline magmas. Geochemical modeling indicates that the precipitation of MoS₂ can be explained simply by the drop in temperature during magmatic differentiation. The occurrence of MoS₂ in pantellerites may result from their high Mo concentrations and low redox state (Ni/NiO=-2.5) relative to metaluminous magmas, causing them to reach MoS₂ saturation at magmatic temperatures. The apparent absence of MoS₂ microphenocrysts in more oxidized, metaluminous rhyolites may indicate that Mo is dissolved primarily as a hexavalent ion in those magmas.  相似文献   

Model employers and model cities?: Bangalore’s public sector and the rise of the neoliberal city     

H. Jacob Carlson 《Urban geography》2018,39(5):726-745

Bangalore is held up as a model for how cities, particularly in the global south, should develop in the globalized information age, in which entrepreneurs with new access to international capital fuel service-sector-driven development. Expanding market forces cultivate cities of skilled middle-class workers whose increased consumption generates broad developmental benefits. Now known as the “Silicon Valley of India,” Bangalore was previously the capital of India’s public sector enterprises (PSEs), which laid important groundwork for the city of today, including the IT sector. I show how, by providing access to homeownership along with high wages and benefits tied to secure employment, Bangalore’s PSEs created the foundation for the city today and its middle-class character. The skilled workforce that PSEs created helped the IT sector emerge in the city. By examining this erased history, we see the role of the state in development projects, and consider alternative models for urban change.  相似文献   

ENVIRONMENTAL DEGRADATION IN BRAZILIAN AMAZONIA: PERSPECTIVES IN US NEWS MEDIA*     

Jacob Bendix  Carol M. Liebler 《The Professional geographer》1991,43(4):474-485

While news media play a major role in shaping public opinion and government policy, existing literature suggests that coverage of both the third world and environmental issues is superficial and crisis-oriented. This study uses the example of Amazonian deforestation to explore the quantity and content of coverage in influential American newspapers. We found that coverage included a wide range of (sometimes) contradictory theories regarding the causes of deforestation, and that the amount, but not the nature, of the coverage changed in response to a “crisis.”  相似文献