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1.
《CT理论与应用研究》1987,(1)
南京工学院CT成象技术的研究是从1982年初开始的。在韦钰教授等中年教师的带领下,开始了CT成象方面的理论和实验研究。1982年申请了中国科学院自然科学基金,非几何光学学成象理论的研究,当年12月,就做出了国内第一张微波CT图象,虽然CT成象的传动装置很原始,但是经过实验人员仔细认真的测试,克服了泄漏场干扰等难点,做出一张清晰的鸭 相似文献
2.
本文分两个部分。第一部分从理论上探讨了全息成象应用于探测时的特点,提出了“全息探测成象”的概念。指出对地层介质使用弹性波或电磁波时,关键问题是纵向分辨力低。作者从信息论和天线阵理论的观点探讨了单频全息成象,研究全息成象和相关检测、匹配滤波以及相控阵之间的联系,提出了多频合成全息探测成象作为解决纵向分辨力的一个方法。探讨了它的原理,指出了它和“脉冲全息成象”的关系,导出了纵向分辨力公式,并给出了二维理论模型计算的结果,以说明方法的可行性和应用前景。 第二部分为实验部分,叙述了多频合成微波全息探测成象的试验。采用二维干涉型全息图做了简单模型的水槽试验,由计算机成象的结果证实了多频合成法的高分辨力和良好的成象质量。 相似文献
3.
井间电阻率层析成象的某些进展 总被引：7，自引：2，他引：7
用有限元法作电阻率层析成象的核心问题是Ｊａｃｏｂｉ矩阵的求取和反演成象算法的研究。本文主要论述了这两方面的最新进展，即求取Ｊａｃｏｂｉ矩阵的格林函数法，用于反演成象计算的平滑度约束反演。文中通过理论模型的成象计算，比较了两种反演算法的成象效果。 相似文献
4.
井间电阻率层析成象的几个问题研究 总被引：2，自引：0，他引：2
井间电阻率层析成象是一种较新的高精度电法勘探方法，尚有许多问题需要探讨。本文针对平滑度约束反演算法，研究了平滑因子及迭代次数对成象结果的影响，给出了约束条件的施加方法。 相似文献
5.
对三峡地区的Ｐｇ波非纵观测资料用地震层析成象方法进行了计算处理并对解释结果作了分析。简要阐述了地震析成象处理方法，地震走时数据的采集与分析等。基底面成象图给出了许多有意义的信息；该测区低速区的开矿要起因于岩性的差异及断层破碎带；基底面上存在３个ｖ〉６．４ｋｍ／ｓ的高速度区，面积最大的一个大体呈南北走向，位于黄陵背斜西南侧、向北进入背斜区，另两个分别位于黄陵背斜东则与测区西侧。 相似文献
6.
在简述了全息成象的一般原理, 并讨论了全息成象应用于钻孔电波勘探的物理基础之后, 着重介绍了多重全息图的概念及其合成成象技术.指明了对钻孔电波勘探的多次定点观测曲线和多次同步观测曲线, 可利用多重全息图及合成成象技术进行联合处理, 以提高分辨力和成象质量.并证明这相当于接收天线阵和发射天线阵依次聚焦在每一成象点上的双聚焦扫描成象的过程.文中对双孔透射法和单孔反射法都进行了讨论, 并给出了相应的计算公式;然后讨论了资料处理中的几个问题, 如发射点象的干扰及其消除、透射全息的屏蔽区问题、水平同步成象时的双象问题等, 并同时介绍了用衍射点模型进行计算机模拟的结果。最后给出了对水槽模型试验资料的处理结果和野外资料的试算结果. 相似文献
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在磁共振成象（ＭＲＩ）中,对各种不同情况如何获取高分辨图象是一个比较复杂的技术问题,与很多参数,因素有关,本文给邮了图象分辨率和图象信噪比,机器灵敏度等参数的制约关系,及在理想情况下分辨率和场梯度,采集时间的定量关系,针对旨在观察单细胞的ＮＭＲ显微镜成象,分析了扩散对极限分辨率（μｍ）的限制。针地人体定域高分辨成象介绍了几种避免图象分析叠（ａｌｉａｓｉｎｇ）的方法,阐述了高分辨成象与脉冲序列的关系 相似文献
9.
本文所涉及的“地震层析成象技术”是在广义上理解的,其内容有:一)地震波速度V或速度的微扰动δ_v的空间层析成象,地震波品质因数Q值或Q值的微扰动δ_Q的空间层析成象;二)与地震监测预报有关的地球物理涉及震源状况有关的成象技术; 相似文献
10.
用Pg波走时重建华北地区结晶基底速度及时间项图像 总被引：3，自引：0，他引：3
应用层析成象以投影方法，对华北地区２８条深地震剖剖面地震测深剖面Ｐｇ波走时进行处理，作出该区结晶基底速度及时间项成像。并作了方法的数值模型合成数据的敏感性分析，证明所采用有效性及成象结果的可靠性。计算中应用ＬＳＱＲ算法求解大型稀疏超定方程。并采用只存储矩阵非零元素技术，使存储量减小到原矩阵百分之一，同时零元素不参数加计算，提高了运算速度。华北地区结昌基底速度为５．９－６．３５ｋｍ／ｓ，时间最大为２ 相似文献
11.
Soil moisture is an important component of the water cycle and will be measured for the first time on a global scale by a dedicated passive L-band microwave radiometer that is planned for launch in 2008. Here, the contribution of topography to the error budget is examined for a vegetated scene with uniform microwave emission. Dual-polarization brightness temperature curves were generated over a range of look angles for 1-D scenes with simple geometrical features, and the soil moisture was retrieved assuming a flat surface. The errors were small for the scenarios considered. Theoretical errors were tested for realistic topography with a DEM transect of a mountainous region, and were found to be comparable. Knowledge of the mean slope from high-resolution DEM data can be used to improve the accuracy of the retrieval. 相似文献
12.
Observations of high-resolution data on radio refractivity were obtained by the airborne microwave refractometer over the Indian sub-continent (a tropical country) from 1971 to 1988. Detailed vertical and horizontal distributions of radio refractivity on a near-real-time basis in the atmospheric boundary layer were determined. Radiosonde observations cannot detect the thin refractivity gradients which characterize the propagation environment in this low-altitude region. This knowledge is required to design reliable and efficient communication systems for strategic, tactical and operational needs. However, the results demonstrate the layer structures and the variability of the boundary layer in time and space. The radio refractive effects on electromagnetic propagation and the future direction of radio refractivity fine-structure measurements are discussed. 相似文献
13.
《Physics of the Earth and Planetary Interiors》2005,148(2-4):193-214
Absolute palaeointensity results were obtained from 392 samples (166 of 241 flows) from the upper 779 m of the Scientific Observation Hole 1 (SOH1) basalt core, Kilauea volcano, Hawaii, using the microwave palaeointensity technique. Based on K–Ar dates and a previously published age model, this covers the last 45 ka thus giving a high-resolution record of geomagnetic intensity in Hawaii. Comparisons with other Hawaiian absolute palaeointensity data show similar trend of higher intensity than present day for the last 3 ka and then a general decrease in intensity over the last 45 ka, though this study reports consistently lower palaeointensity values. Direct comparison with previous Thellier data from the SOH1 core shows some discrepancies between the two methods, with the Thellier data yielding generally higher palaeointensity estimates than the microwave data. In view of these discrepancies between the two methods, the introduction of raw palaeointensity data into the public domain is suggested. 相似文献
14.
Issues associated with microwave link rainfall estimation such as the effects of spatial and temporal variation in rain, the nonlinearity of R–k relations, temporal sampling, power resolution, and wet antenna attenuation are investigated using more than 1.5 years of data from a high-resolution X-band weather radar. Microwave link signals are generated for different link frequencies and lengths from these radar data, so that retrieved path-averaged rainfall intensities can be compared to true path-averaged values. Results of these simulations can be linked to the space–time structure of rain. A frequency-dependent relation between the rainfall intensity at an antenna and the attenuation caused by its wetting is derived using microwave link and rain gauge data. It is shown that if the correct temporal sampling strategy is chosen, the effects of the degradation of power resolution and of wet antenna attenuation (if a correction is applied) are minor (i.e., MBE and bias-corrected RMSE are >−20% and <20% of the mean rainfall intensity, respectively) for link frequencies and lengths above ∼20 GHz and ∼2 km, respectively. 相似文献
15.
MARK F. MEIER 《水文科学杂志》2013,58(3):307-330
Abstract Monitoring of snow and ice on the Earth's surface will require increasing use of satellite remote sensing techniques. These techniques are evolving rapidly. Active and passive sensors operating in the visible, near infrared, thermal infrared, and microwave wavelengths are described in regard to general applications and in regard to specific USA or USSR satellites. Meteorological satellites (frequent images of relatively crude resolution) and Earth resources satellites such as Landsat (less frequent images of higher resolution) have been used to monitor the areal extent of seasonal snow, but problems exist with cloud cover or dense forest canopies. Snow mass (water equivalent) can be measured from a low-flying aircraft using natural radioactivity, but cannot yet be measured from satellite altitudes. A combination of active and passive microwave sensors may permit this kind of measurement, but not until more is known about radiation scattering in snow. Satellite observations are very useful in glacier inventories, correcting maps of glacier extent, estimating certain mass balance parameters, and monitoring calving or surging glaciers. Ground ice is virtually impossible to monitor from satellites; ice on rivers and lakes can be monitored only with very high-resolution sensors. Microwave sensors, due to their all-weather capability (the ability to see through clouds) provide exciting data on sea ice distribution. Analysis of digital tapes of satellite data requires the archiving and scanning of huge amounts of data. Simple methods for extracting quantitative data from satellite images are described. 相似文献
16.
ZHANG Zizhan & LU Yang . Institute of Geodesy Geophysics Chinese Academy of Sciences Wuhan China . Graduate School of the Chinese Academy of Sciences Beijing China . Unite Center for Astro-geodymics Research Chinese Academy of Sciences Shanghai China 《中国科学D辑(英文版)》2005,48(11):2040-2048
The mean sea surface height (MSSH) refers to the average of the long-term sea height. The quasi-sea surface topography (QSST) is usually defined as the height difference between the MSSH and the geoid. As to 100 years of time yardstick of geodesy, the time that satellite altimetry data sets spanned is relatively shorter, in this paper, the QSST refers to the residual sea surface height (RSSH) that shows the height dif-ference between MSSH derived from altimetry and the geoid[1]. As w… 相似文献
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复杂多变的陆地表微波比辐射率,造成陆面上星载微波观测反演大气参数较为困难,也使得许多卫星微波资料不易同化应用到数值模式,因此迫切需要提供准确可靠的陆面微波地表比辐射率信息.随着卫星观测技术的迅速发展,利用丰富的星载被动微波观测直接反演陆面微波比辐射率成为一种主要手段.国外针对星载微波成像仪和微波垂直探测器开展较为系统的陆面微波比辐射率研究,建立不同类型的地表比辐射率反演方法,开发地表比辐射率参数化方法并应用于辐射资料同化.对于卫星观测反演陆面微波比辐射率存在的问题,开展了评估分析和方法订正.国内利用卫星观测也开展了一些陆面微波比辐射率研究工作,尚需要系统、综合的提炼.对于地表特征复杂的中国地区,还需要评估认识不同陆面微波比辐射率反演方法在我国适用情况,需要增强陆面微波比辐射率数据质量的认识以及业务应用. 相似文献
19.
LAURENCE C. SMITH 《水文研究》1997,11(10):1427-1439
The growing availability of multi-temporal satellite data has increased opportunities for monitoring large rivers from space. A variety of passive and active sensors operating in the visible and microwave range are currently operating, or planned, which can estimate inundation area and delineate flood boundaries. Radar altimeters show great promise for directly measuring stage variation in large rivers. It also appears to be possible to obtain estimates of river discharge from space, using ground measurements and satellite data to construct empirical curves that relate water surface area to discharge. Extrapolation of these curves to ungauged sites may be possible for the special case of braided rivers. Where clouds, trees and floating vegetation do not obscure the water surface, high-resolution visible/infrared sensors provide good delineation of inundated areas. Synthetic aperture radar (SAR) sensors can penetrate clouds and can also detect standing water through emergent aquatic plants and forest canopies. However, multiple frequencies and polarizations are required for optimal discrimination of various inundated vegetation cover types. Existing single-polarization, fixed-frequency SARs are not sufficient for mapping inundation area in all riverine environments. In the absence of a space-borne multi-parameter SAR, a synergistic approach using single-frequency, fixed-polarization SAR and visible/infrared data will provide the best results over densely vegetated river floodplains. © 1997 John Wiley & Sons, Ltd. 相似文献
20.
Bhaskar J. Choudhury 《Surveys in Geophysics》1991,12(1-3):63-84
Physical principles governing passive microwave remote sensing of hydrological variables are outlined and illustrated by actual observations by ground-based, air-borne and space-borne microwave radiometers operating at different frequencies. Specific hydrological variables addressed in this paper are soil moisture, seasonal inundation of rivers and swamps, vegetation, snow, and rainfall. Passive remote sensing provides measurements of electromagnetic radiation emitted by the land-atmosphere system, which can be related more directly to the radiative characteristics of the system than to physical or physiological characteristics. Estimation of hydrological variables from microwave observations necessarily involves models relating the radiative to the physical characteristics, and in general more than one physical characteristics determine the microwave observations. This non-uniqueness in the relationship between microwave observations to a particular hydrological variable leads to uncertainties in the estimation of the variable. Notwithstanding this limitation, the principles and the examples given in this paper illustrate the value of passive microwave observations to regional and global hydrology at a temporal resolution of days aggregated to a decade. 相似文献