排序方式： 共有29条查询结果，搜索用时 15 毫秒
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J. R. Kuhn K. S. Balasubramaniam G. Kopp M. J. Penn A. J. Dombard H. Lin 《Solar physics》1994,153(1-2):143-155
Full Stokes polarimetry is obtained using the National Solar Observatory Vacuum Tower Telescope at Sacramento Peak while observing the magnetically sensitive infrared Fei line at wavelength of 1.56. A technique is described which makes use of the high magnetic resolution in this spectral range to remove instrumental polarization from observed StokesQ, U, andV line profiles.Supported under a USAF/AFOSR research initiative.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. 相似文献
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Thomas R. Metcalf K. D. Leka Graham Barnes Bruce W. Lites Manolis K. Georgoulis A. A. Pevtsov K. S. Balasubramaniam G. Allen Gary Ju Jing Jing Li Y. Liu H. N. Wang Valentyna Abramenko Vasyl Yurchyshyn Y.-J. Moon 《Solar physics》2006,237(2):267-296
We report here on the present state-of-the-art in algorithms used for resolving the 180° ambiguity in solar vector magnetic
field measurements. With present observations and techniques, some assumption must be made about the solar magnetic field
in order to resolve this ambiguity. Our focus is the application of numerous existing algorithms to test data for which the
correct answer is known. In this context, we compare the algorithms quantitatively and seek to understand where each succeeds,
where it fails, and why. We have considered five basic approaches: comparing the observed field to a reference field or direction,
minimizing the vertical gradient of the magnetic pressure, minimizing the vertical current density, minimizing some approximation
to the total current density, and minimizing some approximation to the field's divergence. Of the automated methods requiring
no human intervention, those which minimize the square of the vertical current density in conjunction with an approximation
for the vanishing divergence of the magnetic field show the most promise. 相似文献
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A comparison of vector magnetograms from the marshall space flight center and mees solar observatory
R. S. Ronan F. Q. Orrall D. L. Mickey E. A. West M. J. Hagyard K. S. Balasubramaniam 《Solar physics》1992,138(1):49-68
We compare completely independent vector magnetic field measurements from two very different polarimetric instruments. The Marshall Space Flight Center's imaging vector magnetograph is based on a birefringent filter, routinely measuring all four Stokes parameters integrated over the filter bandpass (1/8 Å) which is tunable across the Fei 5250 line in 10 mÅ steps. The Haleakala Stokes Polarimeter of the Mees Solar Observatory (MSO) is based on a spectrometer, routinely measuring all four Stokes parameters of the Fei 6302.5 line simultaneously and then spatially scanning to build up a vector magnetogram. We obtained active region magnetic field data with both the Marshall Space Flight Center (MSFC) and MSO systems on five days during June 1985. After interpolating the MSFC vector fields onto the more coarse spatial grid of MSO we make a point-by-point comparison of the two vector fields for data obtained on two of these days (June 8 and 9). From this comparison we conclude: (1) the spatially-averaged line-of-sight components agree quite well; (2) although the MSO spatial grid is coarser, the quality of the MSO image is better than that of the MSFC data because of better seeing conditions; (3) the agreement between the transverse magnitudes is affected by the poor image quality of the MSFC data; and (4) if the effects of Faraday rotation caused by including line-center linear polarization in the method of analysis are taken into account, the azimuths show good agreement within the scatter in the data caused by the averaging process.National Research Council Resident Research Associate. 相似文献
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Determination of joint roughness coefficient (JRC) for slope stability analysis: a case study from the Gold Coast area, Australia 总被引：2，自引：1，他引：1
Surface roughness of rock discontinuities is an important factor that determines the strength characteristics of rock mass. Joint roughness coefficient (JRC), which is typically measured by means of Barton’s combs in the field, is widely used to describe the joint roughness. However, this traditional method of measurement can be rather subjective, labor-intensive and time consuming. In contrast, photogrammetry can provide an alternative method to obtain relatively simple and fast measurements of JRC based on high resolution 3D models. However, the reliability of such measurements still remains an issue as the results from photogrammetry can be affected by the quality of images. This study seeks to clarify whether photogrammetry can produce accurate measurements of JRC that can be used to assess the stability of slopes. A rock slope with a recent wedge failure in the Gold Coast area, Australia was selected for this purpose, and three different methods such as manual measurements, photogrammetry, and tilt tests were employed to determine the JRC. The obtained results showed some discrepancy in the values of JRC obtained from these three different measurements. In particular, the JRC obtained using the Barton’s comb had slightly higher values compared to those determined through the photogrammetry method while the tilt test results tended to yield overestimated values of JRC. Computer analysis using Universal Distinct Element Code was also performed to study the effect of JRC variation on the slope stability. It was found that an increase in the JRC led to an increase in the safety factor of the slope. 相似文献
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M. S. Kirk K. S. Balasubramaniam J. Jackiewicz B. J. McNamara R. T. J. McAteer 《Solar physics》2013,283(1):97-111
We present a new automated algorithm to identify, track, and characterize small-scale brightening associated with solar eruptive phenomena observed in Hα. The temporal, spatially localized changes in chromospheric intensities can be separated into two categories: flare ribbons and sequential chromospheric brightenings (SCBs). Within each category of brightening we determine the smallest resolvable locus of pixels, a kernel, and track the temporal evolution of the position and intensity of each kernel. This tracking is accomplished by isolating the eruptive features, identifying kernels, and linking detections between frames into trajectories of kernels. We fully characterize the evolving intensity and morphology of the flare ribbons by observing the tracked flare kernels in aggregate. With the location of SCB and flare kernels identified, they can easily be overlaid on complementary data sets to extract Doppler velocities and magnetic-field intensities underlying the kernels. This algorithm is adaptable to any dataset to identify and track solar features. 相似文献