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151.
152.
The round-trip travel time measurements made by spacecraft laser altimeters are primarily used to construct topographic maps
of the target body. The accuracy of the calculated bounce point locations of the laser pulses depends on the quality of the
spacecraft trajectory reconstruction. The trajectory constraints from Doppler and range radio tracking data can be supplemented
by altimetric “crossovers”, to greatly improve the reconstruction of the spacecraft trajectory. Crossovers have been used
successfully in the past (e.g., Mars Orbiter Laser Altimeter on Mars Global Surveyor), but only with single-beam altimeters.
The same algorithms can be used with a multi-beam laser altimeter, but we present a method using the unique cross-track topographic
information present in the multi-beam data. Those crossovers are especially adapted to shallow (small angle) intersections,
as the overlapping area is large, reducing the inherent ambiguities of single-beam data in that situation. We call those “swath
crossovers”. They prove particularly useful in the case of polar-orbiting spacecraft over slowly rotating bodies, because
all the non-polar crossovers have small intersection angles. To demonstrate this method, we perform a simplified simulation
based on the Lunar Reconnaissance Orbiter (LRO) and its five-beam Lunar Orbiter Laser Altimeter. We show that swath crossovers
over one lunar month can independently, from geometry alone, recover the imposed orbital perturbations with great accuracy
(5 m horizontal, < 1 m vertical, about one order of magnitude smaller than the imposed perturbations). We also present new
types of constraints that can be derived from the swath crossovers, and designed to be used in a precision orbit determination
setup. In future work, we will use such multi-beam altimetric constraints with data from LRO. 相似文献
153.
Digiacomo Flavia Tobler Dominique J. Held Thomas Neumann Thomas 《Geochemical transactions》2020,21(1):1-22
The study presented in this work emerged as a result of a multiyear regional geochemical survey based on low-density topsoil sampling and the ensuing geochemical atlas of Croatia. This study focuses on the Dinaric part of Croatia to expound the underlying mechanisms controlling the mobilities and variations in distribution of potentially harmful elements as observed from different environmental angles. Although serious environmental degradation of the vulnerable karst soil landscapes was expected to occur chiefly through the accumulation of various heavy metals, the most acute threat materialized through the soil acidification (Al-toxicity) affecting the entire Dinaric karst area. This picture surfaced from the analysis of all three investigated discriminant function models employing the abovementioned environmental criteria selected autonomously with respect to the evaluated soil geochemistry, namely, geologic setting, regional placement and land use. These models are presented by not only the characteristic discriminant-function diagrams but also a set of appropriate mathematically derived geochemical maps disclosing the allocations of potential threats to the karst soil landscapes posed by soil acidity. 相似文献
154.
This report describes extensive investigations of the near bottom layer of the Western Baltic (Mecklenburg Bight, Darss Sill and Arkona Basin) which were conducted over a 5 year period to determine the typical structure, vertical thickness, vertical turbulence structure, and spatial and temporal variability of this water mass with regard to the area's particular hydrographic conditions. Series of vertical profiles were obtained using the microstructure profiler MSS86, which is capable of measuring high resolution profiles of temperature, conductivity, current shear, light attenuation and pressure down to the seafloor. The near bottom current structure was simultaneously measured with conventional current metres at fixed depths. A typical vertical density structure of the near bottom layer was found. At all investigation sites the Bottom Boundary Layer was separated from the overlying water mass by a well pronounced thermohaline pycnocline. A homogeneous water layer was situated above the bottom with a mean thickness of 2.2 m and typical variation between 0.5 and 3.5 m. The thickness of both the homogeneous layer and of the near bottom layer vary considerably. It is suggested that horizontal advection is responsible for these fluctuations in thickness. The variation in thickness of the Homogeneous Layer is independent of the local mean current velocity, wind speed and energy dissipation rate. Over periods of about 2 days the thickness of the Homogeneous Layer is determined by the average wind speed. The Bottom Boundary Layer shows its own characteristic dynamic, which is largely decoupled from that of the remaining water body. A logarithmic layer was generally not resolved by the current measurements. From dissipation rate measurements, the wall layer was determined to be 0.9 m thick. There was no significant correlation between the dissipation rate and the local wind speed, or between the dissipation rate and local mean current u100. This means that any simple parameterisation relating u100 or friction velocity to the locally produced turbulence and consequently to the resuspension of sediment is probably not applicable to shallow sea areas with properties like the Western Baltic. The investigation of sediment concentration in the BBL illustrates the importance of local effects combined with advection. The sediment stratified layer covers only the bottom most 50 cm. 相似文献
155.
N. L. Neumann P. N. Southgate G. M. Gibson A. MCintyre 《Australian Journal of Earth Sciences》2013,60(6):1023-1039
The integration of detrital and magmatic U – Pb zircon SHIRMP geochronology with facies analysis has allowed the development of a chronostratigraphic framework for the Leichhardt and Calvert Superbasins of the Western Fold Belt, Mt Isa Inlier. This new event chart recognises three supersequences in the Leichhardt Superbasin: the Guide, Myally and Quilalar Supersequences. The Guide Supersequence spans the interval ca 1800 – 1785 Ma and includes the Bottletree Formation and the Mt Guide Quartzite. Sequence relationships suggest that this sedimentary package represents an asymmetric second-order cycle, recording a thickened transgressive suite of deposits and a comparatively thin second-order highstand. The overlying Myally Supersequence spans the interval ca 1780 – 1765 Ma and includes the Eastern Creek Volcanics and syndepositional Lena Quartzite, and the Myally Subgroup. This package represents a second-order supersequence cycle in which mafic volcanism was initiated during a phase of east – west extension. Following the cessation of volcanism, transgression led to the deposition of the Alsace Quartzite and deeper water Bortala Formation. An increase in the rate of sediment supply over accommodation resulted in progradation and deposition of the Whitworth Quartzite and redbed playa facies of the Lochness Formation as accommodation closed. The Quilalar Supersequence spans the interval ca 1755 – 1740 Ma. Sequence analysis in the eastern part of the Leichhardt River Fault Trough identifies a transgressive suite of facies at the base of this supersequence. Black shales from the upper part of the transgressive deposits characterise the condensed section for this supersequence. Facies analysis indicates that deposition took place in a series of storm-, tide- and wave-dominated shelfal marine depositional systems. Although there are no new depositional age constraints for the younger Bigie Formation, field relationships suggest that it is coeval with, or immediately preceded, the ca 1710 Ma Fiery magmatic event. Therefore, a separate supersequence is defined for the Bigie Formation, the Big Supersequence, even though it may be more genetically related to the Fiery magmatic event. The Big Supersequence, together with the ca 1690 Ma Prize Supersequence, comprise the Calvert Superbasin. The evolution of the Leichhardt and Calvert Superbasins are temporally and spatially related to magmatism. In particular, the new maximum depositional ages for the Guide and Myally Supersequences refine the age of the Eastern Creek Volcanics to ca 1780 – 1775 Ma. The new age for the Weberra Granite is within error of the age for the Fiery Creek Volcanics, indicating that they are both part of the ca 1710 Ma Fiery event. New ages for the Sybella Granite confirm that magmatism associated with this magmatic event is refined to 1680 – 1670 Ma, and is followed by deposition of the Gun Supersequence. Combining the new geochronological constraints with previous work now provides a detailed stratigraphic event framework between 1800 and 1575 Ma for the Western Fold Belt of the Mt Isa Inlier, and allows detailed comparisons and correlations with the Eastern Fold Belt and other Proterozoic terranes. 相似文献
156.
Based on the correlation between discharge and carbonate content of the suspended load of the River Rhine, Germany, a systematic geochemical, mineralogical and granulometric study was carried out to verify whether this geochemical signal is transferred to floodplain deposits and in what way these sediments and their chemostratigraphic characterization can be used as a tool for the reconstruction of the river flood history. The analysis of the time resolved changes in the composition of particulate matter during a flood event revealed that the increase of carbonate content (represented by CaO, Sr) with discharge was coupled to a simultaneous decrease in the relative amount of siliciclastics (K2O, Rb). The association of these two groups of diametrical parameters with specific grain size fractions (carbonates with 40–200 μm; siliciclastics with >200 μm) were found to be slightly shifted relative to each other and showed different gradients during the surging and fading flood wave. This, together with the covariance of elements pertaining to minerals with different density (e.g., carbonate and heavy minerals) suggests a chemical response to the changes in discharge, which is controlled primarily by hydraulic equivalence rather than grain size. There is also a time lag between the amount of suspended load and discharge, with a maximum in suspended load shortly after the peak discharge, when the flood has already started to abate. The flood plain sediments have similar composition to the suspended load, suggesting the direct transfer of the geochemical flood signal to the floodplain sediments. 相似文献
157.
This letter analyzes different approaches for polarimetric optimization of multibaseline (MB) interferometric coherences. Two general methods are developed to simultaneously optimize coherences for more than two data sets. The first method provides every data set with a distinct dominant scattering mechanism (SM). The second optimization method is constrained to use equal SMs at all data sets. As the experimental results indicate, MB coherence optimization does improve the accuracy in the estimation of dominant SMs and the associated interferometric phases. Both methods are evaluated on real data acquired by the German Aerospace Agency (DLR)'s enhanced synthetic aperture radar sensor (ESAR) at L-band. 相似文献
158.
This research investigates the potential impacts of climate change on stormwater quantity and quality generated by urban residential areas on an event basis in the rainy season. An urban residential stormwater drainage area in southeast Calgary, Alberta, Canada is the focus of future climate projections from general circulation models (GCMs). A regression‐based statistical downscaling tool was employed to conduct spatial downscaling of daily precipitation and daily mean temperature using projection outputs from the coupled GCM. Projected changes in precipitation and temperature were applied to current climate scenarios to generate future climate scenarios. Artificial neural networks (ANNs) developed for modelling stormwater runoff quantity and quality used projected climate scenarios as network inputs. The hydrological response to climate change was investigated through stormwater runoff volume and peak flow, while the water quality responses were investigated through the event mean value (EMV) of five parameters: turbidity, conductivity, water temperature, dissolved oxygen (DO) and pH. First flush (FF) effects were also noted. Under future climate scenarios, the EMVs of turbidity increased in all storms except for three events of short duration. The EMVs of conductivity were found to decline in small and frequent storms (return period < 5 years); but conductivity EMVs were observed to increase in intensive events (return period ≥ 5 years). In general, an increasing EMV was observed for water temperature, whereas a decreasing trend was found for DO EMV. No clear trend was found in the EMV of pH. In addition, projected future climate scenarios do not produce a stronger FF effect on dissolved solids and suspended solids compared to that produced by the current climate scenario. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
159.
Pascal Schouwink Ronald Miletich Angela Ullrich Ulrich A. Glasmacher Christina Trautmann Reinhard Neumann Barry P. Kohn 《Physics and Chemistry of Minerals》2010,37(6):371-387
Static elasticity measurements at high pressures were carried out on oriented fluorapatite single crystals, some of which
contained oriented amorphous ion tracks (ITs) implanted with relativistic Au ions (2.2 GeV) from the UNILAC linear accelerator
at GSI, Darmstadt. High-pressure experiments on irradiated and non-irradiated crystal sections were carried out in diamond-anvil
high-pressure cells under hydrostatic conditions. In situ single-crystal diffraction was performed to determine the high-precision
lattice parameters, simultaneously monitoring the widths of X-ray diffraction Bragg peaks. High-pressure Raman spectra were
analyzed with respect to the frequency shift and widths of bands, which correspond to the Raman-active vibrational modes of
the phosphate tetrahedra. Swift heavy ion irradiation was found to induce anisotropic lattice expansion and tensile strain
within the host lattice dependent on the ion-track orientation. The relatively low Grüneisen parameter for the ν
1b(A
g) mode, which has been assigned to originate from the volume fraction of the amorphous tracks, and the γ(ν
1a)/γ(ν
1b) ratio reveals compressive strain on the amorphous ITs. The comparative compressibilities for the host lattice reveal approximately
equivalent bulk moduli, but significantly different pressure derivatives (K
T = 88.4 ± 0.7 GPa, ∂K/∂P = 6.3 ± 0.3 for non-irradiated, K
T = 90.0 ± 1.7 GPa, ∂K/∂P = 3.8 ± 0.5 for irradiated samples). The axial compressibility moduli β
−1 reveal significant differences, which correlate with the ion-track orientation [ba - 1 \beta_{a}^{ - 1} = 240 ± 5 GPa, bc - 1 \beta_{c}^{ - 1} = 361 ± 14 GPa, ∂( ba - 1 ) \left( {\beta_{a}^{ - 1} } \right) /∂P = 11.3 ± 1.2, ∂( bc - 1 ) \left( {\beta_{c}^{ - 1} } \right) /∂P = 11.6 ± 3.4 for irradiation ⊥(100); 246 ± 9 GPa, 364 ± 57 GPa, 9.5 ± 2.9, 14.7 ± 14.1 for irradiation ⊥(001), 230.7 ± 3.6 GPa,
373.5 ± 5.1 GPa, 19.2 ± 1.4, 20.1 ± 1.8 for no irradiation]. Line widths of XRD Bragg peaks in irradiated apatites confirm
the strain of the host lattice, which appears to decrease with increasing pressure. By contrast, the bandwidths of Raman modes
increase with pressure, and this is attributed to increasing strain gradients on the length scale of the short-range order.
The investigations reveal considerable deviatoric stress on the [100]-oriented tracks due to the anisotropic elasticity, while
the compression is uniform for the directions perpendicular to the tracks, which are aligned parallel to the c-axis. This difference might be considered to control the diffusion properties related to the annealing kinetics and its observed
anisotropy, and hence to cause potential pressure effects on track-fading rates. 相似文献
160.
The upper mantle under La Palma,Canary Islands: formation of Si−K−Na-rich melt and its importance as a metasomatic agent 总被引:3,自引:1,他引:3
E. Wulff-Pedersen Else-Ragnhild Neumann B. B. Jensen 《Contributions to Mineralogy and Petrology》1996,125(2-3):113-139
Mantle xenoliths hosted by the Historic Volcan de San Antonio, La Palma, Canary Islands, fall into two main group. Group I consists of spinel harzburgites, rare spinel lherzolites and spinel dunites, whereas group II comprises spinel wehrlites, amphibole wehrlites, and amphibole clinopyroxenites. We here present data on group I xenoliths,
including veined harzburgites and dunites which provide an excellent basis for detailed studies of metasomatic processes.
The spinel harzburgite and lherzolite xenoliths have modal ol−opx−cpx ratios and mineral and whole rock major element chemistry
similar to those found in Lanzarote and Hierro, and are interpreted as highly refractory, old oceanic lithospheric mantle.
Spinel dunites are interpreted as old oceanic peridotite which has been relatively enriched in olivine and clinopyroxene (and
highly incompatible elements) through reactions with basaltic Canarian magmas, with relatively high melt/peridotite ratio.
Group I xenoliths from La Palma differ from the Hierro and Lanzarote ones by a frequent presence of minor amounts of phlogopite (and
amphibole). Metasomatic processes are also reflected in a marked enrichment of strongly incompatible relative to moderately
incompatible trace elements, and in a tendency for Fe−Ti enrichment along grain boundaries in some samples. The veins in the
veined xenoliths show a gradual change in phase assemblage and composition of each phase, from Fe−Ti-rich amphibole+augite+Fe−Ti-oxides+apatite+basaltic
glass, to Ti-poor phlogopite+Cr-diopside±chromite+ Si−Na−K-rich glass+fluid. Complex reaction zones between veins and peridotite
include formation of clinopyroxene±olivine+glass at the expense of orthopyroxene in harzburgite, and clinopyroxene+spinel±amphibole±glass
at the expense of olivine in dunite. The dramatic change in glass composition from the broadest to the narrowest veins includes
increasing SiO2 from 44 to 67 wt%, decreasing TiO2/Al2O3 ratio from >0.24 to about 0.02, and increasing K2O and Na2O from 1.8 to >7.0 wt% and 3.8 to 6.7 wt%, respectively. The petrographic observations supported by petrographic mixing calculations
indicate that the most silicic melts in the veined xenoliths formed as the result of reaction between infiltrating basaltic
melt and peridotite wall-rock. The highly silicic, alkaline melt may represent an important metasomatic agent. Pervasive metasomatism
by highly silicic melts (and possibly fluids unmixed from these) may account for the enriched trace element patterns and frequent
presence of phlogopite in the upper mantle under La Palma.
Received: 15 January 1996 / Accepted 30 May 1996 相似文献