共查询到20条相似文献，搜索用时 31 毫秒
1.
This paper considers the results of an experiment conducted in May 2002 on the radio path St. Petersburg-Spitsbergen with
a length of D = 2150 km and equipped with instrumentation for oblique ionospheric sounding (OIS). The features of OIS ionograms at various
degrees of magnetic activity are revealed, and a comparison of these ionograms with the vertical sounding (VS) data at the
Sodankyla observatory (Finland) is performed. This observatory is located near the reflection point of the path in question.
In order to estimate the auroral absorption, riometer data from the Sodankyla observatory were included in the analysis of
the OIS and VS ionograms. The merits of the OIS method as a diagnostic tool of ionospheroic plasma in comparison with VS at
high latitudes are demonstrated. These merits are mainly formulated for magnetically disturbed periods: in the presence of
B events (black-outs), anomalous sporadic Es formations, and a series of other events. 相似文献
2.
The problem of radiosignal reflection from a plane layered isotropic ionosphere has been considered. The vertical sounding ionograms for ionospheric layers with a complicated structure have been modeled. It has been demonstrated that the structure of reflected signals depends on the degree of ionospheric irregularities. Diffuse reflection of radiosignals, caused by the vertical irregularity of the ionosphere, has been detected. 相似文献
3.
Autoscala: an aid for different ionosondes 总被引：1，自引：1，他引：0
Michael Pezzopane Carlo Scotto Łukasz Tomasik Igor Krasheninnikov 《Acta Geophysica》2010,58(3):513-526
Autoscala is a software to automatically scale ionospheric characteristics from an ionogram. Initially it was only applied
to the ionograms recorded by the AIS-INGV ionosondes installed at Rome and Gibilmanna (Italy), and Tucumán (Argentina), that
are not able to record the polarization of the received echo. Recently, Autoscala was also applied to the ionograms recorded
by the AIS-Parus ionosonde installed at Moscow (Russia), that is not able to tag the received echo in terms of polarization,
and by the VISRC2 ionosonde installed at Warsaw (Poland) that is instead able to perform the polarization tagging of the ordinary
and extraordinary echoes. This work shows different examples of processing performed on ionograms recorded by all these three
different types of ionosondes. 相似文献
4.
The series of ionograms of the satellite radio sounding from altitudes below the ionospheric maximum, which were called a delayed lower track, is considered. The method for analyzing ionograms in such a series has been described. The appearance of the delayed lower track on ionograms is explained by the presence of a large ionospheric inhomogeneity which turns radiowaves of many frequencies toward a satellite. It has been assumed that the series of ionograms diagnoses the same inhomogeneity, the structural parameters of which can be determined. The electron density profiles in individual vertical sections of inhomogeneity and the inhomogeneity plasma frequency gradient have been presented, and an attempt to construct the spatial model of inhomogeneity has been made. 相似文献
5.
本文针对单道最小二乘自适应匹配滤波方法在一次波和多次波分量不正交的情况下不能获得正确匹配的问题,提出均衡拟多道最小二乘自适应匹配滤波方法,该方法采取在空间方向上均衡的办法,使得均衡范围内记录中的一次波和多次波分量总是正交的,并结合拟多道最小二乘自适应匹配能更好匹配记录波形的特点,使得该方法取得很好的自适应匹配效果.通过对简单模型、SEG/EAGE SMAART模型和实际资料压制多次波的处理,结果表明该方法效果良好. 相似文献
6.
P. Stauning 《Annales Geophysicae》1995,13(4):450-453
Lacuna on ionograms indicate conditions where the usual ionospheric reflections of vertically propagating radio waves transmitted from and subsequently received by an ionosonde are missing over a range of frequencies. Reflections from the lowermost E-region should still be observable contrary to the more usual cases where absorption processes in the underlying D-region removes the low-frequency part of the ionospheric reflections appearing in ionograms. It is emphasized below that lacuna cases related to E-region processes should be distinguished from lacunae related to processes in the F1 and F2 regions. This distinction appears to have been neglected in a recent paper. 相似文献
7.
电离层垂直探测方法获得的频高图是电离层观测中历史最为悠久的资料,利用现代微电子和计算机技术对大量历史胶片频高图的数字化转换、分析和保存,已成为拯救保护和利用这些珍贵历史资料的十分紧迫和重要的工作.本文采用数字和图像处理等技术对胶片频高图像进行数字化、校正、修复和格式转换,并开发出胶片频高图分析与转换程序,结合常用的SAO Explorer软件对武汉地区的胶片频高图进行了实例的分析.结果表明,该方法具有较好的可靠性和通用性,对大量历史频高图的数字化转换和分析具有实用性. 相似文献
8.
完全匹配层(PML)作为一种稳定高效的吸收边界条件,广泛应用于基于一阶电磁波动方程的探地雷达(GPR)数值模拟中.为解决基于二阶电磁波动方程的GPR数值模拟的吸收边界问题,本文借鉴二阶弹性波动方程的PML边界条件构建思想,提出了一种适合二阶电磁波动方程GPR时域有限元模拟的PML边界条件.从二阶电磁波动方程出发,基于复拉伸坐标变换,推导了PML算法的频域表达式;通过合理构造辅助微分方程,得到了PML算法的时域表达式,并以变分形式(弱形式)加载到GPR时域有限元方程中,实现了PML边界条件在二阶电磁波动方程GPR时域有限元模拟中的应用.在此基础上,对比了无边界条件、Sarma边界条件和PML边界条件下均匀模型的波场快照、单道波形、时域反射误差和能量衰减曲线,结果表明:PML边界条件的吸收效果要远优于Sarma边界条件,具有近似零反射系数.一个复杂介质模型的正演模拟验证了PML边界条件在非均匀地电结构中电磁波传播模拟的良好吸收效果. 相似文献
9.
为研究地震子波相位对反射系数序列反演的影响,在自回归滑动平均(ARMA)模型描述子波的基础上,提出采用z域对称映射ARMA模型零极点的方法构造了一系列相同振幅谱、不同相位谱的地震子波,并结合谱除法对人工合成地震记录进行反射系数序列反演.理论分析表明,子波相位估计不准时反射系数序列反演结果中残留一个纯相位滤波器,该纯相位滤波器的相位谱为真实子波和构造子波的相位谱之差.采用丰度和变分作为评价方法,在反演结果中确定出真实的或准确的反射系数序列.仿真实验和实际数据处理结果也验证了子波相位对反射系数序列反演的影响规律和评价方法的有效性,为进一步提高反射系数序列反演结果精度指明了研究方向. 相似文献
10.
《Journal of Atmospheric and Solar》2005,67(12):1063-1073
The performance of a computer program, called Autoscala, for the automatic scaling of foF2 and MUF(3000)F2 from ionograms has been extensively tested. Results of comparisons between automatically and manually scaled data are shown both for Autoscala and for ARTIST (release 4.01). Particular attention has been paid to the cases in which the ionograms have a truncated trace. The problem of the rejection of bad quality ionograms has been also considered. The analysis of data shows that the reliability of values automatically given as output by Autoscala is good. For the data set considered Autoscala seems to operate better than ARTIST. 相似文献
11.
Complex ionograms from the Intercosmos-19 satellite with strongly delayed and sometimes multiple reflections from the Earth are considered. An analysis shows that these reflections are usually associated with sharp horizontal gradients of the ionospheric plasma. Such gradients are formed on the walls of the main ionospheric trough, at peaks of electron density, and on the inner and, especially frequently, on the outer slope of the crest of the equatorial anomaly. In one case, distant reflections from the Earth (DREs) formed near the equator, when the satellite in perigee was lower than the F2-layer maximum height. A quantitative interpretation of the most typical cases of DREs is given based on ray tracing. For this purpose, the model of the ionosphere under the satellite is developed, ray paths are calculated, and model ionograms are formed. The good agreement between experimental and model ionograms allows us to conclude that the task of interpreting complicated ionograms obtained by Intercosmos-19 with DRE has been solved successfully. 相似文献
12.
Indrajit G. Roy 《Geophysical Prospecting》2020,68(3):1041-1056
We propose a strategy in designing an optimal set of filter parameters, such as the order of interpolating polynomial and the filter length for a Savitzky–Golay derivative filter. The proposed strategy is based on the ‘principle of parsimony’ while satisfying the optimality conditions. The optimality conditions are based on the Durbin–Watson lag-1 test statistic and the Derringer–Suich desirability function. While the former checks for an appropriate data fitting, the latter, on the other hand, ensures minimal shape distortion of the reconstructed response. The proposed strategy of designing filter parameters is developed and validated through numerical experiments using Gaussian pulse as a test function which is contaminated with additive white Gaussian noise. In the numerical tests, the polynomial orders used were 3, 5 and 7, but the filter length for each polynomial was varying until the optimality conditions were satisfied. The Savitzky–Golay derivative filtering is used in obtaining the robust reconstruction of noisy geophysical anomaly and the robust estimation of its first- and second-order derivatives. We validated the proposed technique on the published self-potential anomaly data using a data-based interpretation technique where the reconstructed anomaly and its first- and second-order derivatives were used in estimating model parameters. The data-based interpretation using the proposed technique of Savitzky–Golay derivative filtering provides a close agreement with the published results. 相似文献
13.
Study of sporadic-E clouds by backscatter radar 总被引：1，自引：0，他引：1
It is shown that swept-frequency backscatter ionograms covering a range of azimuths can be used to study the dynamics of sporadic-E clouds. A simple technique based on analytic ray tracing can be used to simulate the observed narrow traces associated with Es patches. This enables the location and extent of the sporadic-E clouds to be determined. The motion of clouds can then be determined from a time sequence of records. In order to demonstrate the method, results are presented from an initial study of 5 days of backscatter ionograms from the Jindalee Stage B data base obtained during March-April 1990. Usually 2–3 clouds were observed each day, mainly during the evening and up to midnight. The clouds lasted from 1–4 h and extended between 30°–80° in azimuth and 150–800 km in range. The clouds were mostly stationary or drifted generally westward with velocities of up to 80 ms–1. Only one cloud was observed moving eastward. 相似文献
14.
The purpose of this paper is to study the effect of the main ionospheric trough location on the form of oblique sounding ionograms on the Murmansk-St. Petersburg subauroral radio path. Using a mathematical model of the high-latitude ionosphere, we have calculated four different distributions of electron density along the radio path. One of the distributions has been obtained when the trough is absent, and the remaining three distributions contain troughs of approximately identical depth and width but located at different distances from the ends of the radio path. Using the program of two-dimensional ray tracing, we numerically synthesized oblique-incidence ionograms for each of the four obtained distributions of electron density. The calculations have shown that the location of the main ionospheric trough affects considerably the shape of oblique-incidence ionograms. 相似文献
15.
16.
目的：为提高瞬变电磁探测精度，提出用反射系数作为特征量来对地下电性分界面成像，给出了方法的数学模型和实现步骤，并给出从实测数据中提取反射系数，对电性界面实现成像的思路，资料和方法：由野外实测资料出发，在频率域内用数字滤波技术计算波阻抗，再通过域的变换在时间域内建立含有反射系数的方程组。结果：最终后通过线性规划法求出反射系数，并以此值为参数来绘制成像断面。结论：数值模拟结果和实例的应用结果表明方法正确、有效。方法本身提高了瞬变电磁对电性层的分辨能力。 相似文献
17.
H.
ZDEM&#x;R 《Geophysical Prospecting》1985,33(6):828-860
A seismic trace is modeled as a moving average (MA) process both in signal and noise: a signal wavelet convolved with a reflection coefficient series plus colored random noise. Seismic reflection coefficients can be estimated from seismic traces using suitable estimation algorithms if the input wavelet is known and vice versa. The maximum likelihood (ML) algorithm is used to estimate the system order and the reflection coefficients. The system order is related to the arrival time of the latest signal in a complex seismic reflection event. The least-squares (LS) method does not provide such information. The ML algorithm makes assumptions only about the Gaussian nature of the noise. It is better suited for seismic applications since the LS method inherits the white noise assumption. The Gauss-Newton (G-N) and Newton-Raphson (N-R) optimization algorithms are used to obtain the ML and the LS estimates. Reflection coefficient estimations are affected by the choice of sampling rate of seismic data. Theoretically, the optimum choice in system identification is the Nyquist rate. Experience with synthetic data confirms the theory. In practice, good estimates of reflection coefficients are possible only up to certain pulse separations (or, equivalently, orders). This is mostly due to numerical problems with the optimization algorithms used and partly due to the limited bandwidth of seismic signals. Good estimates from data simulated using three airgun array pulses recorded with 6–128 Hz filter setting are possible up to about 40.0 ms pulse separations. Successful estimations from pinchout and thin layer simulations and well controlled offshore “bright-spots” are given. 相似文献
18.
Calculations using the Sheffield University plasmasphere ionosphere model have shown that under certain conditions an additional layer can form in the low latitude topside ionosphere. This layer (the F3 layer) has subsequently been observed in ionograms recorded at Fortaleza in Brazil. It has not been observed in ionograms recorded at the neighbouring station São Luis. Model calculations have shown that the F3 layer is most likely to form in summer at Fortaleza due to a combination of the neutral wind and theE × B drift acting to raise the plasma. At the location of São Luis, almost on the geomagnetic equator, the neutral wind has a smaller vertical component so the F3 layer does not form. 相似文献
19.
20.
O. A. Laryunin 《Geomagnetism and Aeronomy》2018,58(2):245-251
The characteristic U-shaped traces (cusps) in ionograms are associated with the passage of traveling ionospheric disturbances (TIDs), which lead to horizontal electron density gradients in the ionosphere and, therefore, to off-angle reflections in radio sounding. A new form of representation is considered for daily ionospheric sounding data. A compound parabolic layer model is proposed, which allows analytical calculation of ray paths to speed up the “homing-in” of the rays. Changes in the shape of the trace in the ionogram due to varying the TID characteristics are examined. A discussion is given of the possibilities for estimating TID characteristics from digitized vertical sounding ionograms. 相似文献