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31.
Calibrating the GOCE accelerations with star sensor data and a global gravity field model 总被引:1,自引:0,他引:1
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
32.
Johannes Bouman Sietse Rispens Thomas Gruber Radboud Koop Ernst Schrama Pieter Visser Carl Christian Tscherning Martin Veicherts 《Journal of Geodesy》2009,83(7):659-678
One of the products derived from the gravity field and steady-state ocean circulation explorer (GOCE) observations are the
gravity gradients. These gravity gradients are provided in the gradiometer reference frame (GRF) and are calibrated in-flight
using satellite shaking and star sensor data. To use these gravity gradients for application in Earth scienes and gravity
field analysis, additional preprocessing needs to be done, including corrections for temporal gravity field signals to isolate
the static gravity field part, screening for outliers, calibration by comparison with existing external gravity field information
and error assessment. The temporal gravity gradient corrections consist of tidal and nontidal corrections. These are all generally
below the gravity gradient error level, which is predicted to show a 1/f behaviour for low frequencies. In the outlier detection, the 1/f error is compensated for by subtracting a local median from the data, while the data error is assessed using the median absolute
deviation. The local median acts as a high-pass filter and it is robust as is the median absolute deviation. Three different
methods have been implemented for the calibration of the gravity gradients. All three methods use a high-pass filter to compensate
for the 1/f gravity gradient error. The baseline method uses state-of-the-art global gravity field models and the most accurate results
are obtained if star sensor misalignments are estimated along with the calibration parameters. A second calibration method
uses GOCE GPS data to estimate a low-degree gravity field model as well as gravity gradient scale factors. Both methods allow
to estimate gravity gradient scale factors down to the 10−3 level. The third calibration method uses high accurate terrestrial gravity data in selected regions to validate the gravity
gradient scale factors, focussing on the measurement band. Gravity gradient scale factors may be estimated down to the 10−2 level with this method. 相似文献
33.
Richard A. Staff Takeshi Nakagawa Gordon Schlolaut Michael H. Marshall Achim Brauer Henry F. Lamb Christopher Bronk Ramsey Charlotte L. Bryant Fiona Brock Hiroyuki Kitagawa Johannes van der Plicht Rebecca L. Payne Victoria C. Smith Darren F. Mark Alison Macleod Simon P. E. Blockley Jean‐Luc Schwenninger Pavel E. Tarasov Tsuyoshi Haraguchi Katsuya Gotanda Hitoshi Yonenobu Yusuke Yokoyama Suigetsu Project Members 《Boreas: An International Journal of Quaternary Research》2013,42(2):259-266
The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high‐resolution, multi‐proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well‐constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree‐ring) time scale, as derived using radiocarbon data from the uppermost (non‐varved) portion of the core. This tie‐point, defined as a distinct (flood) marker horizon in SG06 (event layer B‐07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range). 相似文献
34.
Dendrochronological analysis was applied to subfossil remains of Scots pine (Pinus sylvestris L.) buried in a South Swedish peat deposit. In combination with peat stratigraphy, this approach was explored for its potential to provide information on the local hydrological and depositional history at the site, forming the basis for a regional palaeohydrological analysis. A 726‐year ring‐width chronology was developed and assigned an absolute age of 7233–6508 cal a BP (5284–4559 BC) through cross‐dating with German bog‐pine chronologies, whereas two short additional records of older ages were radiocarbon dated. Registration of growth positions of individual trees allowed assessment of the spatial dynamics of the pine population in response to hydrological changes and peatland ontogeny. Annually resolved growth variability patterns in the pine population reveal several establishment and degeneration phases, probably reflecting fluctuations in bog‐surface wetness. A major establishment phase at 7200–6900 cal a BP reflects the onset of a period of lowered groundwater level, also indicated by increased peat humification, and a development consistent with regional temperature and lake level reconstructions revealed from other proxies. This study demonstrates that subfossil bog‐pine populations may provide annually to decadally resolved reconstructions of local groundwater variability, which are highly relevant in a long‐term palaeoclimatic context. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
35.
A projection of future sea level 总被引:1,自引:0,他引:1
Johannes Oerlemans 《Climatic change》1989,15(1-2):151-174
Evidence is reviewed that suggests faster sea-level rise when climate gets warmer. Four processes appear as dominating on a time scale of decades to centuries: melting of mountain glaciers and small ice caps, changes in the mass balance of the large polar ice sheets (Greenland, Antarctica), possible ice-flow instabilities (in particular on the West Antarctic Ice Sheet), and thermal expansion of ocean water.For a given temperature scenario, an attempt is made to estimate the different contributions. The calculation yields a figure of 9.5 cm of sea-level rise since 1850 AD, which is within the uncertainty range of estimates of the observed rise.A further 33 cm rise is found as most likely for the year 2050, but the uncertainty is very large ( = 32 cm). The contribution from melting of land ice is of the same order of magnitude as thermal expansion. The mass-balance effects of the major ice sheets tend to cancel to some extent (increasing accumulation on Antarctica, increasing ablation on Greenland). For the year 2100 a value of 66 cm above the present-day stand is found ( = 57 cm). The estimates of the standard deviation include uncertainty in the temperature scenario, as presented elsewhere in this volume. 相似文献
36.
Statistical distribution models of multi-site binding equilibria have potential applicability in the study of acid-base and metal complexation chemistry of humic substances in soils, sediments, and natural waters. A mathematical derivation is presented for the general continuous model for the case of proton binding; computational methods are described for fitting numerically the parameters in such models. Among models considered are those based on nontruncated, truncated, and bimodal (mixed) distributions. Specific emphasis is placed on Gaussian distribution models. 相似文献
37.
38.
Johannes Schweitzer 《Geophysical Journal International》1995,123(1):260-276
During the Group of Scientific Experts Technical Test (GSETT, second experiment, 22 April-2 June 1991), several hundred seismic events were located in Europe. Associating these events with the detecting stations-altogether 28 European stations including seven arrays participated in the GSETT-2 experiment-clearly shows that the Teisseyre-Tornquist Zone (TTZ) influences the propagation of regional seismic phases. Large explosions in the Bay of Gdańsk, for example, were observed by the well-established Scandinavian arrays'NORSAR (Δ 830km) and ARCESS (Δ 1650km), but not by the Polish station KSP (Δ 470km) nor by the new highly sensitive GERESS array (Δ 750km), both situated south-west of the TTZ. For events in central Europe with comparable magnitudes, we observe a similar increase of the detection threshold at stations located north-east of the TTZ in Scandinavia. to explain these observations, the wave propagation of Pn and Pg perpendicular to the TTZ was modelled for a profile from the Estonian/Russian border region to GERESS with Gaussian-beam seismograms. Published crustal and uppermost mantle models for Poland and for Europe were used as a starting point for developing a model of the TTZ. the observations cannot be explained only by a graben-like crustal structure with a jump in Moho depth from 30km to 50km. to defocus the seismic energy, the TTZ as a structural anomaly between eastern and western Europe must reach down into the upper mantle to a depth of at least about 200 km. the proposed model has such a deep-reaching root of the TTZ. 相似文献
39.
Hydrophobic and electrostatic parameters in bacterial adhesion 总被引:5,自引:0,他引:5
Mark C. M. van Loosdrecht Willem Norde Johannes Lyklema Alexander J. B. Zehnder 《Aquatic Sciences - Research Across Boundaries》1990,52(1):103-114
Recently it has been shown that the initial stages of bacterial adhesion to a model-surface of sulphated polystyrene can best be described using hydrophobic and electrostatic parameters. In the present study it is tested whether these parameters can generally be applied to predict bacterial adhesion by using (i) glass, as a model for hydrophilic and natural surfaces of silicates and oxides, (ii) polystyrene coated with proteins, as a model for a surface coated with an organic layer, and (iii) river Rhine sediment, as an example of a natural surface. Adhesion to glass was dominated by electrostatic interaction, whereas adhesion to polystyrene coated with various types of proteins depended on the surface characteristics of the bacteria and the type of protein. By relating Van der Waals interactions to hydrophobicity of the interacting species, the adhesion of bacteria to the various surfaces including the river Rhine sediments could be interpreted in terms of the DLVO-theory. It is therefore concluded that the conceptual principles of the DLVO-theory (interplay of Van der Waals and electrostatic interactions) are suitable to describe, at least qualitatively, the initial processes of bacterial adhesion to a wide range of surfaces. 相似文献
40.