Calibrating the GOCE accelerations with star sensor data and a global gravity field model   总被引：1，自引：0，他引：1  

Sietse Rispens  Johannes Bouman 《Journal of Geodesy》2009,83(8):737-749

A reliable and accurate gradiometer calibration is essential for the scientific return of the gravity field and steady-state ocean circulation explorer (GOCE) mission. This paper describes a new method for external calibration of the GOCE gradiometer accelerations. A global gravity field model in combination with star sensor quaternions is used to compute reference differential accelerations, which may be used to estimate various combinations of gradiometer scale factors, internal gradiometer misalignments and misalignments between star sensor and gradiometer. In many aspects, the new method is complementary to the GOCE in-flight calibration. In contrast to the in-flight calibration, which requires a satellite-shaking phase, the new method uses data from the nominal measurement phases. The results of a simulation study show that gradiometer scale factors can be estimated on a weekly basis with accuracies better than 2 × 10⁻³ for the ultrasensitive and 10⁻² for the less sensitive axes, which is compatible with the requirements of the gravity gradient error. Based on a 58-day data set, scale factors are found that can reduce the errors of the in-flight-calibrated measurements. The elements of the complete inverse calibration matrix, representing both the internal gradiometer misalignments and scale factors, can be estimated with accuracies in general better than 10⁻³.  相似文献   

Time-dependent greenhouse warming computations with a coupled ocean-atmosphere model     

Ulrich Cubasch  Klaus Hasselmann  Heinke Höck  Ernst Maier-Reimer  Uwe Mikolajewicz  Benjamin D Santer  Robert Sausen 《Climate Dynamics》1993,9(3):165-165

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Searching for an intrinsic stellar population in compact high-velocity clouds     

Ulrich Hopp  Regina E. Schulte-Ladbeck  Jürgen Kerp 《Astrophysics and Space Science》2003,284(2):647-650

We are investigating the hypothesis that Compact High-Velocity Clouds (CHVCs) are the left-over building blocks of Local Group galaxies. To this end, we are searching for their embedded stellar populations using FORS at the VLT. The search is done with single-star photometry in V and I bands, which is sensitive to both, young and old, stellar populations. Five CHVCs of our sample have been observed so far down to I=24. We pointed the VLT towards the highest HI column density regions, as determined in Effelsberg radio data. In an alternate approach, we searched 2MASS public data towards those 5 CHVCs down to K=16. While the VLT data probe the central regions out to distance moduli of about 27, the 2MASS data are sensitive to a population of red giant stars to distance moduli of about 20. The 2MASS data, on the other hand, cover a much wider field of view than the VLT data (radius of 1 degree versus FORS field of 6.8 arcmin). We did not find a stellar population intrinsic to the CHVCs in either data. In this paper, we illustrate our search methods. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

A consistent geochemical modelling approach for the leaching and reactive transport of major and trace elements in MSWI bottom ash     

Joris J. Dijkstra  Johannes C.L. Meeussen  Hans A. Van der Sloot  Rob N.J. Comans 《Applied Geochemistry》2008

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Geochemical characterization of the potential trace metal mobility in cohesive sediments     

Michael Kersten  Ulrich Förstner 《Geo-Marine Letters》1991,11(3-4):184-187

The Acid-Producing Potential (APP) and the Acid-Consuming Capacity (ACC) are introduced as basic parameters for long-term pollution assessment of mud disposal. They can be obtained by a four-step sequential leaching technique. The concentration of Ca extracted by the first Na-acetate step permits calculating the ACC. Both the Fe- and S-fractions deliberated by subsequent leaching steps are used to calculate the APP. When the APP of a sample is substacted from its ACC, a negative value indicates a potential increase of the bioavailability of the toxic metal load upon disposal of this mud in oxic environments.  相似文献   

An evaluation of multi-annual management strategies for ICES roundfish stocks     

Kell  L.T.; Pilling  G.M.; Kirkwood  G.P.; Pastoors  M.A.; Mesnil  B.; Korsbrekke  K.; Abaunza  P.; Aps  R.; Biseau  A.; Kunzlik  P.; Needle  C.L.; Roel  B.A.; Ulrich  C. 《ICES Journal of Marine Science》2006,63(1):12-24

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A seismic reconnaissance survey of the northern Congo Fan     

Gabriele Uenzelmann-Neben  Volkhard Spiess  Ulrich Bleil 《Marine Geology》1997,140(3-4):283-306

To study the time-varying influence of the Congo River and the Benguela Current on the deposition at the Angola Continental Margin, a high-resolution reflection seismic survey was carried out on the northern Congo Fan. Four seismostratigraphic units have been defined for the upper 800 m (1000 ms TWT) of the data. The units record different depositional environments, ranging from pre-establishment of the Congo River drainage system to the influence of the Benguela Current. An indication of a general change in the turbidite system is provided by a shift in channel distribution and a relocation of the depocentre of coarse material. The ascent of salt is recorded up to the Pliocene. Gas that has migrated out of Lower Cretaceous shales and that was produced from large quantities of organic matter in the younger sediments can be found on the flanks and on top of the salt domes. In a few places, this gas even ascends to the ocean floor along structural pathways through the topmost unit.  相似文献   

Spatial variability in growth and reproduction of the Pacific oyster Crassostrea gigas (Thunberg, 1793) along the west European coast     

Joana F.M.F. Cardoso  Denis Langlet  Jos F. Loff  Ana R. Martins  Johannes IJ. Witte  Paulo T. Santos  Henk W. van der Veer 《Journal of Sea Research》2007,57(4):303-315

The Pacific oyster Crassostrea gigas was introduced in Europe for commercial purposes in the mid 1960s. It was initially thought that low winter temperatures would restrain this species' reproduction and settlement; however, its present distribution in areas where no introduction has taken place suggests that natural invasion and expansion has occurred. Along the European coast, wild populations of Pacific oysters are already found from northern Germany to southern Portugal. Whether C. gigas will continue to further expand through northern waters will depend on its physiological performance. In this study, the performance of wild oyster populations has been studied in terms of growth and reproduction at three stations: La Rochelle (France; 46°N), Yerseke (Oosterschelde estuary, The Netherlands, 51°N), and Texel (Wadden Sea estuary, The Netherlands, 53°N). The French population had the lowest somatic-shell mass ratio and an increase in maximum shell length, somatic and gonadal mass was observed from France to the Netherlands. In addition, mean oocyte diameter decreased significantly from south to north. The combination of increasing gonadal mass and decreasing oocyte volume suggests an increasing reproductive output in terms of egg numbers from France to The Netherlands. Differences in temperature between locations will at least be partly responsible for the observed patterns; however, other environmental factors (such as food availability, predation pressure, sediment type and/or seston concentration) cannot be excluded. Since smaller eggs (oocytes) are thought to have a longer development time, the environmental conditions along the Dutch coast may result in increased larval dispersal and possibly in further population expansion.  相似文献   

Growth and reproduction of the bivalve Spisula subtruncata (da Costa) in Dutch coastal waters     

Joana F.M.F. Cardoso  Johannes IJ. Witte  Henk W. van der Veer 《Journal of Sea Research》2007,57(4):316-324

The bivalve Spisula subtruncata is usually abundant in shallow coastal waters along the Dutch coast. However, its biomass has been decreasing since 1995. In order to assess whether reproductive failure may be the cause of the observed decline over the last decades, the energy investment in reproduction of a population of S. subtruncata from central Dutch coastal waters was studied. The population studied consisted of individuals of up to four years old. Shell length reached maximum values of around 32 mm and individual total body, somatic and gonadal ash-free dry mass reached maximum values of about 278 mg AFDM, 252 mg AFDM and 76 mg AFDM, respectively. A clear seasonal cycle in somatic and gonadal mass was observed. Somatic and gonadal mass indices increased in early spring and reached maximum values during summer, followed by a decrease to minimum values at the beginning of the following year. Spawning was in June–July and settlement of spat seems to have occurred in July–August. Mean oocyte diameter was 57.43 ± 0.03 μm, corresponding to a volume of 98972 μm³. These results suggested that reproductive failure was not the cause of the current population decline. Most likely, unsuccessful settlement of spat and/or severe predation during the first months of life were responsible for the observed patterns.  相似文献   

The effect of submarine groundwater discharge on nutrient and salinity regimes in a coastal lagoon off Perth, Western Australia     

R. E. Johannes  C. J. Hearn 《Estuarine, Coastal and Shelf Science》1985,21(6):789-800

Submarine groundwater discharge (SGD) into a coastal lagoon off Perth, Western Australia, contains nitrate and silicate in concentrations two orders of magnitude higher than those of the receiving waters. This discharge delivers enough nitrate to replace that dissolved in the lagoon water mass about every eight days and enough silicate to replace the lagoon silicate in about 48 days. The delivery rate of nitrate nitrogen by SGD is equal to about 48% of that required for observed growth rates of lagoon macrophytes. Surface salinity is lower close to the shore as a result of SGD. During calm conditions a salinity front was observed in the lagoon, with a nearshore pool of nutrient-enriched water floating above the more saline ocean water.  相似文献