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Anastassios E. Petropoulos James M. Longuski 《Celestial Mechanics and Dynamical Astronomy》1994,60(4):431-454
An exact analysis of the coverage obtained by spacecraft using cross-track scanning and nadir-centered conical imaging, under imposed viewing obliqueness and resolution requirements, is presented. In addition to exact expressions for the area acquired and the area acquisition rate, envelope theory is introduced to obtain the boundary of the imaged area. These expressions are relatively compact, allowing rapid machine computation. The effects of the sun phase angle, and of imaging system limitations are also examined. The Galileo mission encounter with Callisto is used as a numerical example, from which certain general conclusions are drawn regarding optimal imaging trajectories. 相似文献
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Luigi R. Bedin † Santi Cassisi Fiorella Castelli Giampaolo Piotto Jay Anderson Maurizio Salaris Yazan Momany Adriano Pietrinferni 《Monthly notices of the Royal Astronomical Society》2005,357(3):1038-1048
We propose a zero-point photometric calibration of the data from the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) on board the Hubble Space Telescope , based on a spectrum of Vega and the most up-to-date in-flight transmission curves of the camera. This calibration is accurate at the level of a few hundredths of a magnitude. The main purpose of this effort is to transform the entire set of evolutionary models into a simple observational photometric system for ACS/WFC data, and to make them available to the astronomical community. We provide the zero-points for the most used ACS/WFC bands, and give basic recipes for calibrating both the observed data and the models. We also present the colour–magnitude diagram from ACS data of five Galactic globular clusters, spanning the metallicity range −2.2 <[Fe/H] < −0.04 , and we provide fiducial points representing their sequences from several magnitudes below the turn-off to the red giant branch tip. The observed sequences are compared with the models in the newly defined photometric system. 相似文献
4.
Interpretation of transient electromagnetic soundings over three-dimensional structures for the central-loop configuration 总被引:2,自引:0,他引:2
Gregory A. Newman Walter L. Anderson Gerald W. Hohmann 《Geophysical Journal International》1987,89(3):889-914
Summary. An assessment is made of the bias of fitting constrained layered-earth models to transient electromagnetic data obtained over 3-D structures. In this assessment we use the central-loop configuration and show that accurate estimates of the depth of burial of 3-D structures can be obtained with layered-earth model fitting. However, layered-earth interpretations are not reliable for estimating depth extents and resistivities of 3-D structures. When layered earths are used for interpretation, it is advantageous in some cases to use data based on the magnetic field instead of the voltage. A magnetic-field definition of apparent resistivity, in contrast to a definition based on the voltage, eliminates apparent-resistivity overshoots and undershoots in the data. A resistivity undershoot in the data can produce an extraneous and misleading layer in an interpretation of a 3-D resistive structure. Due to 3-D effects, apparent-resistivity soundings (magnetic field and voltage) may rise so steeply at late times that it may not be possible to fit a sounding to a reasonable layered-earth model. Truncating such a sounding, over a buried conductor, allows for a reasonable layered-earth fit and an accurate estimate of the depth to the conductor. However, the resistivity of the conductor is overestimated.
Measurements of the horizontal field in the central-loop configuration can map 3-D structures, provided the sensor is located accurately at the centre of the transmitting loop. Horizontal-field calculations show that the transients peak on the flanks of a 3-D structure, but are depressed over the structure's centre. Weak transient responses flanked by two large transient responses, which are opposite in sign, locate the structure. The sign reversal is caused by a corresponding reversal in the currents that are channelled through or deflected away from conductive or resistive structures, respectively. 相似文献
Measurements of the horizontal field in the central-loop configuration can map 3-D structures, provided the sensor is located accurately at the centre of the transmitting loop. Horizontal-field calculations show that the transients peak on the flanks of a 3-D structure, but are depressed over the structure's centre. Weak transient responses flanked by two large transient responses, which are opposite in sign, locate the structure. The sign reversal is caused by a corresponding reversal in the currents that are channelled through or deflected away from conductive or resistive structures, respectively. 相似文献
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运用现代构造解析理论和方法,对新疆可可托海—四川简阳人工地震测深剖面与天然地震面波层析成像进行构造解析基础上,综合地质学、深源岩石包体构造岩石学和地球化学以及其他地球物理学标志等多学科综合研究显示,高速块体或幔块构造的几何结构型式是控制该区岩石圈构造格局和岩石圈表层构造变形基本条件之一。本文建立起该地学断面地壳及岩石圈与软流圈速度结构模型和物质组成结构模型,划分出岩石圈3种几何结构模式:克拉通陆根状结构、造山带楔状结构和高原陆根状结构,以及岩石圈二类构造演化类型:克拉通型岩石圈和增厚型岩石圈。在系统论述断面地壳及岩石圈结构构造类型特征基础上,探讨了该断面软流圈结构特征,岩石圈与软流圈相互作用及其地幔动力学模式。 相似文献
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9.
Michael Riedel 《Marine Geophysical Researches》2007,28(4):355-371
Two single-channel seismic (SCS) data sets collected in 2000 and 2005 were used for a four-dimensional (4D) time-lapse analysis
of an active cold vent (Bullseye Vent). The data set acquired in 2000 serves as a reference in the applied processing sequence.
The 4D processing sequence utilizes time- and phase-matching, gain adjustments and shaping filters to transform the 2005 data
set so that it is most comparable to the conditions under which the 2000 data were acquired. The cold vent is characterized
by seismic blanking, which is a result of the presence of gas hydrate in the subsurface either within coarser-grained turbidite
sands or in fractures, as well as free gas trapped in these fracture systems. The area of blanking was defined using the seismic
attributes instantaneous amplitude and similarity. Several areas were identified where blanking was reduced in 2005 relative
to 2000. But most of the centre of Bullseye Vent and the area around it were seen to be characterized by intensified blanking
in 2005. Tracing these areas of intensified blanking through the three-dimensional (3D) seismic volume defined several apparent
new flow pathways that were not seen in the 2000 data, which are interpreted as newly generated fractures/faults for upward
fluid migration. Intensified blanking is interpreted as a result of new formation of gas hydrate in the subsurface along new
fracture pathways. Areas with reduced blanking may be zones where formerly plugged fractures that had trapped some free gas
may have been opened and free gas was liberated. 相似文献
10.