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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.
3.
本文给出1993—1994年期间,用云南天文台1米望远镜折轴摄谱仪观测获得类太阳色球活动星。εEri的5个波段高分辨、高信噪比光谱,运用两种不同方法:谱线轮廓塞曼致宽分析和多重线统计分析法成功地测定了εEri的表面磁场强度和磁场的覆盖因子,并对这两种磁场测定方法作了简单的讨论. 相似文献
4.
A model of protostar formation under two current carrying gas filaments collision is presented. The model implies MHD approach involving self-gravity and radiative cooling effects. We suppose that through the current carrying gas filament collision a magnetic field reconnection takes place. Using an appropriate self-consistent presentation for time and special dependences of physical quantities in MHD equations, we derive the full set of equations that describes time evolution of the physical quantities just after an occurrence of magnetic field reconnection. Numerical simulations reveal that the process consists of three main phases of evolution. The first is an appearance of preceding peaks in time profiles of density and temperature following by the next phase of depression of both temperature and density and the final fast condensation phase with either cooling or heating of matter depending on initial parameters of problem. Effects of initial conditions like as magnetic field strength, current strength, initial gravity energy, cooling time and a geometry of collision are investigated. Main conclusion is that protostar formation takes place within the time interval less than one free fall time and it is preceded by the appearance of dense and hot matter with lifetime much less than free fall time. The final temperature of the protostar depends on the physical conditions and mainly on the ratio between free fall time and cooling time in the colliding current carrying gas filaments. 相似文献
5.
林菁 《广东海洋大学学报》1996,(1)
分析了分频和CTC计数采样中误读数的原因和解决方法,并利用微机软件实现非线性校正。此传感器用于位移测量系统中,具有0.01mm的分辨率及优于1%的精度,可在-20~60℃温度范围内工作。 相似文献
6.
G. Palladino A. Basili G. Di Cocco T. Franceschini G. Landini S. Silvestri A. Barbini M. Galimberti L. A. Gizzi 《Experimental Astronomy》2006,21(3):169-187
This paper describes the design of a star sensor based upon a high dynamic range CCD in order to reach an arcsec-level attitude
determination in balloon-borne missions. A custom star identification software was developed and laboratory-tested on a prototype
assembled using commercial components. A set of numerical simulations have been carried out to study the dependence on the
pointing precision of the centroid position accuracy, the number of detected stars and the effect of the image focusing. Moreover,
the role of the electronic noise and the discrete pixel structure on the light signals is identified by the analysis of numerical
simulations. Laboratory tests confirm that the arcsec pointing accuracy with a 1 Hz update rate can be achieved with our combination
of custom-developed software and selected hardware components. 相似文献
7.
介绍了一种新颖的静态传感器网络实现方法,它利用可移动的中继节点来收集静态传感器网络的数据,有效的节约各传感器节点的能源,延长整个传感器网络的有效工作时间。也可以对该方法进行适当的改进,应用到某些实时性要求较高的场合中去。然后介绍了应用该原理实现的一个通讯协议。 相似文献
8.
Eduardo E. Alonso Sarah M. Springman Charles W. W. Ng 《Geotechnical and Geological Engineering》2008,26(6):817-826
Two large-scale “in situ” demonstration experiments and their instrumentation are described. The first test (FEBEX Experiment)
involves the hydration of a compacted bentonite barrier under the combined effect of an inner source of heat and an outer
water flow from the confining saturated granite rock. In the second case, the progressive de-saturation of Opalinus clay induced
by maintained ventilation of an unlined tunnel is analyzed. The paper shows the performance of different sensors (capacitive
cells, psychrometers, TDR’s) and a comparison of fill behaviour with modelling results. The long term performance of some
instruments could also be evaluated specially in the case of FEBEX test. Capacitive sensors provide relative humidity data
during long transient periods characterised by very large variations of suction within the bentonite. 相似文献
9.
Alessandro Tarantino Andrew M. Ridley David G. Toll 《Geotechnical and Geological Engineering》2008,26(6):751-782
This paper presents a review of techniques for field measurement of suction, water content, and water hydraulic conductivity
(permeability). Main problems in the use of field tensiometers are addressed and hints on how to improve tensiometer performance
are given. Advantages and limitations of instruments for indirect measurement of suction including electrical conductivity
sensors, thermal conductivity sensors, dielectric permittivity sensors, filter paper, and psychrometer are discussed. Techniques
for water content measurement based on dielectric methods are then presented. These include time and amplitude domain reflectometry
and capacitance. Finally, a brief overview of methods for measurement of water permeability in the field is presented. 相似文献
10.