Multiple longshore sand bars in the upper Chesapeake Bay

In the upper Chesapeake Bay (Maryland, U.S.A.) field surveys were conducted at 18 multiple longshore sand bar sites. The multiple bar systems were found in water depths less than approximately 2 m (mean sea level), and exhibited mild bottom slopes of 0·0052 or less. The number of bars composing each system ranged from four to 17 and the spacing between the crests typically increased in the offshore direction, ranging from 12 to 70 m. Bar height also typically increased with distance offshore and ranged from 0·03 to 0·61 m. A grain size analysis of crest and trough sediment did not reveal any significant differences and the sediment was categorized as ‘fine sand’. A review of the literature data indicated that the Chesapeake Bay multiple bars possessed similar characteristics to those found in Gelding Bay (Baltic Sea); similarities in fetch, wave height and tidal range between the two bays may account for this finding. The surf-scaling parameter indicated that the multiple bar systems were extremely dissipative with regard to wave energy, and wave height appeared to be an important factor in controlling bar spacing and bar height. A multiple wave break point hypothesis was discussed as a possible mechanism for the formation of Chesapeake Bay multiple longshore bars, and limited observational evidence appeared to support such a mechanism.     

A multi‐level parallelized substructuring‐frontal solution for coupled thermo/hydro/mechanical problems in unsaturated soil

This paper proposes a multi‐level parallelized substructuring–frontal combined algorithm for the analysis of the problem of thermo/hydraulic/mechanical behaviour of unsaturated soil. Temperature, displacement, pore water pressure and pore air pressure are treated as the primary variables in a non‐linear analysis. Details are given firstly of the substructuring–frontal combined approach. The incorporation of the algorithm in a multi‐level parallel strategy is then discussed. The parallel processing can thus be carried out at different substructural levels. The method thus developed impacts, in a positive way, on both computer storage requirement and execution time. Copyright © 2003 John Wiley & Sons, Ltd.     

The equatorial photospheric rotation rate

The equatorial photospheric rotation rate has been observed on 14 days in 1978–1980. The resulting rotation rate, = 14.14±0.04°/day, is 2% slower than the rate as observed for long-lived sunspots.Stationed at Kitt Peak National Observatory.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.     

Thermal evolution of an extensional detachment as constrained by organic metamorphic data and thermal modeling: Graz Paleozoic Nappe Complex (Eastern Alps)

Following Early Cretaceous nappe stacking, the Eastern Alps were affected by late-orogenic extension during the Late Cretaceous. In the eastern segment of this range, a Late Cretaceous detachment separates a very low- to low-grade metamorphic cover (Graz Paleozoic Nappe Complex, GPNC) above a low- to high-grade metamorphic basement. Synchronously, the Kainach Gosau Basin (KGB) collapsed and subsided on top of the section.Metamorphism of organic material within this section has been investigated using vitrinite reflectance data and Raman spectra of extracted carbonaceous material. In the southern part of the GPNC, vitrinite reflectance indicates a decrease in organic maturity towards the stratigraphic youngest unit. The remaining part of the GPNC is characterized by an aureole of elevated vitrinite reflectance values and Raman R2 ratios that parallels the margins of the GPNC. Vitrinite reflectance in the KGB shows a steep coalification gradient and increases significantly towards the western basin margin. The observed stratigraphic trend in the southern GPNC is a result of deep Paleozoic to Early Cretaceous burial. This maturity pattern was overprinted along the margins by advective heat and convective fluids during Late Cretaceous to Paleogene exhumation of basement rocks.During shearing, the fault zone was heated up to ca. 500 °C. This overprint is explained by a two-dimensional thermal model with a ramp-flat fault geometry and a slip rate of 1 to 1.5 cm/year during 5 Ma fault movement. The collapse basin above the detachment subsided in a thermal regime which was characterized by relaxing isotherms.     

Sea‐level and ocean‐current control on carbonate‐platform growth,Maldives, Indian Ocean

Multichannel high‐resolution seismic and multibeam data were acquired from the Maldives‐isolated carbonate platform in the Indian Ocean for a detailed characterization of the Neogene bank architecture of this edifice. The goal of the research is to decipher the controlling factors of platform evolution, with a special emphasis on sea‐level changes and changes of the oceanic currents. The stacking pattern of Lower to Middle Miocene depositional sequences, with an evolution of a ramp geometry to a flat‐topped platform, reflects variations of accommodation, which here are proposed to be primarily governed by fluctuations of relative sea level. Easterly currents during this stage of bank growth controlled an asymmetric east‐directed progradation of the bank edge. During the late middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank demise and associated sediment‐drift deposition. This turnover is attributed to the onset and/or intensification of the Indian monsoon and related upwelling and occurrence of currents, locally changing environmental conditions and impinging upon the carbonate system. Mega spill over lobes, shaped by reversing currents, formed as large‐scale prograding complexes, which have previously been interpreted as deposits formed during a forced regression. On a regional scale, a complex carbonate‐platform growth can occur, with a coexistence of bank‐margin progradation and aggradation, as well as partial drowning. It is further shown that a downward shift of clinoforms and offlapping geometries in carbonate platforms are not necessarily indicative for a sea‐level driven forced regression. Findings are expected to be applicable to other examples of Cenozoic platforms in the Indo‐Pacific region.     

Are numerical weather model outputs helpful to reduce tropospheric delay signals in InSAR data?

Interferometric synthetic aperture radar phase data include not only signals due to crustal movements, but also those associated with microwave propagation delay through the atmosphere. In particular, the effect of water vapor can generate apparent signals in the order of a few centimeters or more, and prevent us from detecting such geophysical signals as those due to secular crustal deformation. To examine if and to what extent numerical weather model (NWM) outputs are helpful to reduce the tropospheric delay signals at spatial scales of 5–50 km wavelengths, we compared three approaches of tropospheric signal reduction, using 54 interferograms in central Hokkaido, Japan. The first approach is the conventional topography-correlated delay correction that is based on the regional digital elevation model (DEM). The second approach is based on the Japan Meteorological Agency’s operational meso-scale analysis model (MSM) data, where we compute tropospheric delays and subtract them from the interferogram. However, the MSM data are available at predefined epochs and their spatial resolution is about 10 km; therefore, we need to interpolate both temporally and spatially to match with interferograms. Expecting to obtain a more physically plausible reduction of the tropospheric effects, we ran a 1-km mesh high-resolution numerical weather model WRF (Weather Research and Forecasting model) by ourselves, using the MSM data as the initial and boundary conditions. The third approach is similar to the second approach, except that we make use of the WRF-based tropospheric data. Results show that if the topography-correlated phases are significant, both the conventional DEM-based approach and the MSM-based approach reveal comparable performances. However, when the topography-correlated phases are insignificant, none of the approaches can efficiently reduce the tropospheric phases. Although it could reduce the tropospheric signals in a local area, in none of the case studies did the WRF model produce the “best” performance. Whereas the global atmospheric model outputs are shown to be effective in reducing long-wavelength tropospheric signals, we consider that further improvements are needed for the initial and boundary condition data for high-resolution NWM, so that the NWM-based approach will become more reliable even in the case of a non-stratified troposphere.     

A comparison of three image-object methods for the multiscale analysis of landscape structure

Within the conceptual framework of Complex Systems, we discuss the importance and challenges in extracting and linking multiscale objects from high-resolution remote sensing imagery to improve the monitoring, modeling and management of complex landscapes. In particular, we emphasize that remote sensing data are a particular case of the modifiable areal unit problem (MAUP) and describe how image-objects provide a way to reduce this problem. We then hypothesize that multiscale analysis should be guided by the intrinsic scale of the dominant landscape objects composing a scene and describe three different multiscale image-processing techniques with the potential to achieve this. Each of these techniques, i.e., Fractal Net Evolution Approach (FNEA), Linear Scale-Space and Blob-Feature Detection (SS), and Multiscale Object-Specific Analysis (MOSA), facilitates the multiscale pattern analysis, exploration and hierarchical linking of image-objects based on methods that derive spatially explicit multiscale contextual information from a single resolution of remote sensing imagery. We then outline the weaknesses and strengths of each technique and provide strategies for their improvement.     

0.99999999 confidence ambiguity resolution with GPS and Galileo

In this short contribution it is demonstrated how integer carrier phase cycle ambiguity resolution will perform in near future, when the US GPS gets modernized and the European Galileo becomes operational. The capability of ambiguity resolution is analyzed in the context of precise differential positioning over short, medium and long distances. Starting from dual-frequency operation with GPS at present, particularly augmenting the number of satellites turns out to have beneficial consequences on the capability of correctly resolving the ambiguities. With a 'double' constellation, on short baselines, the confidence of the integer ambiguity solution increases to a level of 0.99999999 or beyond. Electronic Publication