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��׷�  �ؽ���  ������  ���κ�  ������  ����־ 《大地测量与地球动力学》2014,34(6):81-85

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山体效应对北半球林线分布的影响(英文)     

赵芳  张百平  庞宇  姚永慧 《地理学报(英文版)》2014,(2)

Alpine timberline, as the "ecological transition zone," has long attracted the attention of scientists in many fields, especially in recent years. Many unitary and dibasic fitting models have been developed to explore the relationship between timberline elevation and latitude or temperature. However, these models are usually on regional scale and could not be applied to other regions; on the other hand, hemispherical-scale and continental-scale models are usually based on about 100 timberline data and are necessarily low in precision. The present article collects 516 data sites of timberline, and takes latitude, continentality and mass elevation effect(MEE) as independent variables and timberline elevation as dependent variable to develop a ternary linear regression model. Continentality is calculated using the meteorological data released by WorldClim and mountain base elevation(as a proxy of mass elevation effect) is extracted on the basis of SRTM 90-meter resolution elevation data. The results show that the coefficient of determination(R2) of the linear model is as high as 0.904, and that the contribution rate of latitude, continentality and MEE to timberline elevation is 45.02%(p=0.000), 6.04%(p=0.000) and 48.94%(p=0.000), respectively. This means that MEE is simply the primary factor contributing to the elevation distribution of timberline on the continental and hemispherical scales. The contribution rate of MEE to timberline altitude differs in different regions, e.g., 50.49%(p=0.000) in North America, 48.73%(p=0.000) in the eastern Eurasia, and 43.6%(p=0.000) in the western Eurasia, but it is usually very high.  相似文献   

大气透射仪与前向散射仪低能见度条件下跑道视程数据对比分析     

范大伟  Cao Dunbo  Zhu Guodong  Xiao Kaiqian 《沙漠与绿洲气象(新疆气象)》2019,13(4):58-63

利用2017年10月26日—2018年3月14日期间,乌鲁木齐机场跑道视程≤600 m时跑道25方向大气透射仪和前向散射仪的跑道视程数据,以及跑道25方向大气透射仪和中间段大气透射仪跑道视程数据进行对比分析,得到以下结论:(1)大气透射仪的跑道视程数据大于等于前向散射仪的跑道视程数据的比例为96%,跑道视程≤400 m时,两种设备相互替代性较好;(2)相比于黑夜,白天情况下前向散射仪的跑道视程数据更接近25方向大气透射仪的跑道视程数据;(3)相比于跑道中间段大气透射仪,跑道25方向前向散射仪跑道视程数据更接近25方向的大气透射仪跑道视程数据。  相似文献   

Constituents of Vertical-component Coda Waves at Long Periods     

Takuto Maeda  Haruo Sato  Masakazu Ohtake 《Pure and Applied Geophysics》2006,163(2-3):549-566

Aki (1969) first modeled coda waves of a local earthquake as a superposition of scattered surface waves. This paper attempts to clarify the constituents of surface-wave coda at long periods at very long lapse times. For a large earthquake of magnitude 7 or larger, vertical component oscillation in periods from 90 to 180 s persists for more than 20 hours from the earthquake origin time. Although the early portion of the coda envelope is successfully modeled by assuming incoherent scattered Rayleigh waves by heterogeneities distributed all over the Earth, the later potion of the observed coda envelope (roughly later than 35,000 s) has systematically larger amplitude than theoretical prediction. To clarify the cause of this discrepancy, we studied the constituents of vertical-component seismograms of three large earthquakes recorded by the F-net in Japan using the f-k power spectral analysis. We found that the direct and scattered fundamental-mode Rayleigh waves of velocity about 3.7 km/s are dominant in the earlier part of each envelope. It justifies the use of a scattering model of the fundamental Rayleigh waves for synthesizing the envelope. At lapse times later than 20,000 s–35,000 s, higher modes with phase velocities around 20 km/s become dominant. The transition time to the dominance of higher modes is found to become earlier for a deeper focus earthquake. The small coda attenuation factor from (1.90±0.23) × 10⁻³ to (2.38±0.32) × 10⁻³ estimated from later coda envelopes recorded at IRIS stations distributed worldwide also agrees with the attenuation factor of spheroidal modes according to PREM. We may interpret that higher mode waves are uniformly distributed at large lapse time due to large velocity dispersion and/or scattering and they dominate over the fundamental mode waves because of smaller attenuation in the lower mantle. The coda attenuation measurement proposed by Aki is found to be useful even for long periods and at very large lapse times.  相似文献   

九华山复式杂岩体的构成及主要特征   总被引：5，自引：1，他引：5  

钟华明  姚仲伯  许卫 《安徽地质》1996,(3)

九华山复式杂岩体由东堡岩体、上菥荻岩体和天台岩体三部分构成。它们之间呈不同形式的侵入接触。各岩体的空间分布、岩浆演化及内部构造等特征均显示它们的独立性。在岩石学、地球化学等方面三者均有明显区别，定位机制也各具特色，东堡岩体以顶蚀作用为主，上菥荻岩体为破火山口沉陷式，天白岩体则为岩墙扩张式定位。  相似文献   

SH波在浅埋多个圆孔处的散射与地震动   总被引：1，自引：0，他引：1  

姜艳  黄荣富  刘殿魁  王国庆 《地震工程与工程振动》2004,24(1):7-14

研究了以任意方向入射的平面SH波在浅埋多个圆孔处的散射与地震动问题。利用SH散射的对称性和多极坐标方法构造了问题的位移解。当入射波的波长与圆孔的半径相比较小时,地震动将受到较大的影响。影响地震动有三个主要参数:(1)SH波的入射角α0;(2)入射波波数η,即圆形孔洞的半径与入射波半波长之比;(3)诸圆孔的埋置情况,诸孔的埋深hi/ai、孔心距Di/ai,即圆形孔洞至表面距离与圆半径之比和圆形孔洞中心的距离与半径之比。当η较大时,地震动幅值变化激烈,位移幅值可出现跳动和放大的现象。当诸圆孔的最小埋深量hi/ai和孔心距Di/ai超过10-12时,位移幅值恢复至半空间单一圆孔散射的情况,表明圆形孔洞的影响可被忽略。  相似文献   

连续傍轴近似公式及其多种离散形式   总被引：5，自引：2，他引：3  

张晓志  谢礼立 《地震工程与工程振动》2004,24(5):1-6

基于单向波动法向透射的一般运动学模型和局部多项式插值函数,推导建立了连续形和2阶离散形法向透射傍轴近似公式。指出连续形傍轴近似公式具有多种离散形式,本文给出的标准形式、已有的多次透射公式和平面波多项式外推公式都是连续形傍轴近似公式的不同离散形式,因此具有基本相当的精度、稳定性和计算效率以及相同的普适性和局限性。  相似文献   

Curvelet 域海底电缆多次波压制方法研究     

郝振江  冯飞  王德利  赵伟 《世界地质》2013,32(1):130-136

将检波点置于海底的海底电缆( OBC) 地震采集技术面临全体自由表面多次波的困扰。通过采用改进后的SRME 方法进行OBC 数据自由表面多次波的衰减,SRME 方法分为预测和相减过程,在相减过程中采用常规减去法、二维Curvelet 阈值相减法以及三维Curvelet 阈值相减进行多次波相减。通过模型试算对3 种方法进行比较,发现在Curvelet 阈值相减法中,对多次波的减去效果更好,尤其是三维Curvelet 变换阈值相减的效果更为突出。  相似文献   

GNSS-R海面目标成像仿真方法研究     

张元迪  焦瑞莉  朱云龙  吴世玉 《测绘通报》2019,(2):86-90,107

结合物理光学法及传统复合电磁散射计算模型中的"四路径"方法，以GNSS信号为信号源，提出了一种基于高频散射理论的GNSS-SAR成像模型，建模过程考虑了多路径散射、遮蔽、漫散射等效应，较好地描述了电磁散射效应对海面场景GNSS-SAR成像的影响。根据电磁散射效应，分析了海面风速对成像效果产生的干扰情况，发现在本文仿真场景下，9 m/s风速海背景下的目标能够被识别出来，17 m/s风速海背景下的目标几乎淹没在海杂波中。  相似文献   

Oblique surface wave propagation over a small undulation on the bottom of an ocean     

S. C. Martha 《地球物理与天体物理流体动力学》2013,107(2):65-80

The problem of oblique water wave diffraction by small undulation of the bottom of a laterally unbounded ocean is considered using linear water wave theory. A perturbation analysis is employed to obtain the velocity potential, the reflection and the transmission coefficients up to the first order in terms of integrals involving the shape functions c(x) representing the bottom undulation. Finite cosine transform is used to find the first order potential, and this potential is utilised in obtaining the first order reflection and transmission coefficients. Some particular forms of the shape function representing an exponentially damped undulation, a single hump and a patch of sinusoidal ripples are considered and the integrals for the reflection and transmission coefficients are evaluated. For the exponentially damped undulation, it is observed that the reflection ceases much before transmission while for the single hump, reflection and transmission go hand in hand up to a certain value of the wavenumber, after which they vanish. For the patch of sinusoidal ripples having the same wavenumber, the reflection coefficient up to the first order is found to be an oscillatory function in the quotient of twice the component of the wavenumber along x-axis and the ripple wavenumber. When this quotient becomes one, the theory predicts a resonant interaction between the bed and free surface, and the reflection coefficient becomes a multiple of the number of ripples. High reflection of the incident wave energy occurs if this number is large. Also, when a patch of ripples having different wavenumbers is considered the same result follows. Known results for the normal incidence are recovered as special cases for the patch of sinusoidal ripples. The theoretical observations are shown computationally.  相似文献