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1.
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
2.
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
3.
Wojciech Stopiński Gienadiy A. Sobolev Aleksandr W. Ponomaryov Vladimir Los 《Pure and Applied Geophysics》1991,136(1):49-58
Making measurements of electric resistivity at 16 s intervals, the authors noticed fast changes of this parameter prior to the occurrence of the main fracture. The changes are superposed on bay pulsations of increasing amplitude and decreasing period. This finding opens prospects for a wider use of an electric resistivity method and proves the high quality of automatic instruments, in particular their high resolution. It also gives evidence for the occurrence of short-period precursors in the fracture zone while the main fracture is being formed. 相似文献
4.
Chen Xuezhong Yin Xiangchu Aki K Ouyang H Jin A. Song Zhiping and Wang YucangCenter tor Analysis Prediction SSB Beijing ChinaSouthern California Eanhquake Center University of Southern California Los Angeles USAInstitute of Geophysics SSB Beijing China 《中国地震研究》1996,(4)
The load/unload response ratio YQ with the geophysical parameter coda Q-1 of the crust as response is denned in this study.The variation in YQ-1 before and after the Northridge earthquake of January 17,1994(California)has been investigated by using the data of coda Q-1 with frequencies of 1.5,3.0,6.0,12.0,and 24.0 Hz in the Southern California from 1987 to 1994.It can be found that YQ-1 for coda waves with all frequencies,the frequency of 12.0 Hz excluded,ascended to a certain extent prior to the occurrence of the rnainshock and returned to normality after the main shock. 相似文献
5.
The results of hardware and methodological developments for recording of electromagnetic emission (EME) generated by rock
samples under loading in laboratory experiments are presented. The results of experiments with the instruments developed are
described. The facilities developed made it possible to measure reliably the electromagnetic emission under conditions of
high background of electromagnetic noise and to reduce the level of reliably recorded signals as compared with previous experiments.
The results of observation of the appearance of electromagnetic emission in the experiments with the rock samples under laboratory
conditions showed a high correlation of the time instants of generation of the electromagnetic emission and the changes of
its parameters with the changes in the reactive resistivity of the rock sample and seismoacoustic emission activity in the
controlled area of the sample. It is revealed that electromagnetic emission occurs and reaches its maximum on the descending
branch of the plot of polarizability during rock destruction. 相似文献
6.
The details of a general multiblock partial least squares(PLS)algorithm based on one originallypresented by Wold et al.have been developed and are completely presented.The algorithm can handlemost types of relationships between the blocks and constitutes a significant advancement in the modelingof complex chemical systems.The algorithm has been programmed in FORTRAN and has been testedon two simulated multiblock problems,a three-block and a five-block problem.The algorithm combinesthe score vectors for all blocks predicting a particular block into a new block.This new block is used topredict the predicted block in a manner analogous to the two-block PLS.In a similar manner if one blockpredicts more than one other block,the score vectors of all predicted blocks are combined to form a newblock,which is then predicted by the predictor block as in the two-block PLS.Blocks that both predictand are predicted are treated in such a way that both of these roles can be taken into account whencalculating interblock relationships.The results of numerical simulations indicate that the computerprogram is operating properly and that the multiblock PLS produces meaningful and consistent results. 相似文献
7.
Direct observations as well as Normalized Difference Vegetation Index (NDVI) data from satellites have shown earlier leaf appearance in the northern hemisphere, which is believed to result from climate warming. The advance of leaf out to earlier times in the year could be limited or even reversed, however, as temperate and boreal trees require a certain amount of chilling in winter for rapid leaf out in spring. If this chilling requirement is not fulfilled, an increasing amount of warming is required. Implications of these chilling requirements at the biome level are not clear. One approach to estimate their importance is to generalize the exponential relationships between chilling and warming established for single species. Previous work using NDVI data suggests that this is indeed feasible but much has been limited to specific biomes or a very few years of data for the modelling. We find chilling requirements for northern temperate and boreal biomes by fitting various phenology models to green-up dates determined from NDVI using various methods and 12 years of data. The models predict that in northern middle and high latitudes the advance of green-up will be limited to a total of 4 to 5 days on average (but up to 15 days regionally) over the time period 2000–2060 as estimated using two contrasting climate simulations. This results from the exponentially increasing warming requirements for leaf out when winter chilling falls below a threshold as shown by a comparison with models that consider only spring warming. The model evaluation suggests an element of regional adaptation of the warming required for leaf out in large biomes. 相似文献
8.
Correction of tree ring stable carbon isotope chronologies for changes in the carbon dioxide content of the atmosphere 总被引：2，自引：0，他引：2
Danny McCarroll Mary H. Gagen Iain Robertson Sietse Los Risto Jalkanen John S. Waterhouse 《Geochimica et cosmochimica acta》2009,73(6):1539-114
Tree-ring stable carbon isotope ratios (δ13C) often display a decline over the industrial period (post-AD1850) that is only partly explained by changes in the isotopic ratio of carbon dioxide (CO2) and may represent a response to increased atmospheric concentrations of CO2 (ca). If this is not addressed, reconstructions using long tree-ring stable isotope chronologies calibrated using the modern period, for which meteorological records are available, may be compromised. We propose a correction procedure that attempts to calculate the δ13C values that would have been obtained under pre-industrial conditions. The correction procedure uses nonlinear (loess) regression but the magnitude of the adjustment made is restricted by two logical constraints based on the physiological response of trees: first, that a unit increase in ca cannot result in more than the same unit increase in the internal concentration of CO2 (ci), and second, that increases in water-use efficiency as a result of an increase in ca are limited to maintaining a constant ci/ca ratio. The first constraint allows retention of a falling trend in δ13C, which exceeds that which could logically be attributed to a passive response to rising ca. The second constraint ensures that any increase in δ13C, reflecting a change in water-use efficiency beyond maintenance of a constant ci/ca, is not removed. The procedure is tested using ‘pseudoproxies’, to demonstrate the effect of the correction on time-series with different shapes, and data from three sites in Finland and Norway. Two of the time-series retain a significant trend after correction, and in all three cases the correction improves the correlation with local meteorological measurements. 相似文献
9.
10.
在民间传说中,“银弹”是杀死狼人和女巫的有效武器。在地震预测中,“银弹”就是“具有诊断价值的前兆”,即地震前观测到的以高概率表明即将来临地震事件的时间、地点和震级的信号。Crampin在其述评中声称,剪切波分裂（SWS）观测提供了一枚“银弹”。由此,他断言地震学能够将地震预测从我们最近在“见解”栏目中指定的低概率环境中解脱出来。 相似文献