Linear models in vertical ionosperic sounding

Summary The paper deals with selecting optimum models for computing the vertical distribution of the electron concentration of ionospheric plasma. It is demonstrated that, with a view to the proposed average criterion, a model can be found, which utilizes the information contained in observed values to a better advantage than previous models.     

Modeling of vertical sounding ionograms for nonmonotonous ionospheric layers

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.     

Estimation of ionospheric radiowave absorption based on one vertical sounding ionogram

A method for estimating absorption value on the basis on one ionogram of a vertical sounding dynasonde was proposed. The main idea is that averaging the amplitudes of the signals reflected from the ionosphere is replaced over time by frequency averaging of the amplitude factor introduced by the authors. The amplitude factor was determined. The regularities of daily variations in the amplitude factor are discussed.     

电离层斜测数据集

电离层斜测数据集包括F₂层临界频率数据和最大电子密度空间分布图,来源于中国地震电离层监测试验网观测数据。2008年汶川地震后,中国地震局地震预测研究所和中国电子科技集团第22研究所,在国防科技工业电波环境观测站网原有的稀疏发射站网基础上,根据地震重点监测区带分布和区域数据覆盖能力的双重需要,利用电离层对地基发射信号的反射特性,在华北5个电离层垂测发射站的基础上,建立了20个电离层斜测接收站,形成100条发射—接收链路,达到以经济手段取得电离层加密监测的效果。数据由接收台站接收后,汇聚到北京数据中心,并建立Oracle数据库,将数据入库。通过人工判读,生成可应用的电离层斜测观测数据。此数据集通过数据共享网站提供数据共享服务,可为地震系统内部各省地震局和研究所进行地震监测预测研究以及系统外部科研机构和院校电离层观测研究提供基础数据。     

与地震有关的电离层扰动的甚低频/低频无线电探测

近期人们认识到,电离层对地震影响非常敏感,探测与地震有关的电离层扰动看来对地震短临预测是非常有前途的。我们提出可利用甚低频／低频（3～30kHz／30-300kHz）无线电探测进行地震-电离层扰动的探测。1995年神户地震明显发现电离层扰动现象之后,开始了利用低电离层甚低频／低频传播信号进行地震短临预测的简短历史。在说明先前的甚低频／低频结果之后,我们给出了最新的甚低频／低频发现：一个是电离层扰动与地震在统计上相关,第二个是2004年12月苏门答腊地震的实例研究,说明了这次地震电离层扰动的空间尺度和动力学原理。     

A vertical sounding of severe haze process in Guangzhou area

We detected a severe haze process in Guangzhou area with lidar and microwave radiometer, performed an inversion to get boundary layer height by wavelet covariance transform, and analyzed the correlation between meteorological factors of boundary layer and visibility from the perspective of dynamical and thermodynamic structures. Our results indicate that the boundary layer height shows significant daily changes, consistent with ground visibility variation. During the cleaning process, the boundary layer height exceeded 1 km; during severe haze, the height was only 500 m. Temperature gradient of 50–100 m, which was 30 h lag, was remarkably correlated with visibility, with the correlation coefficient of 0.77. High layer visibility(255 m) and low layer stability were significantly anticorrelation, and the maximum anticorrelation coefficient was up to-0.76 in cleaning days and-0.49 in haze days. In the related boundary layer meteorological factors, surface ventilation coefficient was linearly correlated with ground visibility, with the greatest correlation coefficient of 0.88. The correlation coefficients of boundary layer height, ground wind velocity, relative humidity and ground visibility were 0.76, 0.67, and-0.77, respectively. There was a strong correlation between different meteorological factors. The dominant meteorological factor during this haze process was surface ventilation coefficient. In the area without boundary layer height sounding, ground visibility and wind velocity could be used to estimate boundary layer height.     

Studying large-scale traveling ionospheric disturbances according to the data of oblique-incidence sounding

The morphological features of wave-like ionospheric disturbances with periods of 1–2 h and the spatial extent exceeding 1000 km are studied. Oblique-incidence sounding data of the ionosphere, obtained in eastern Siberia during several continuous monthly experiments on three radio paths from 2006 to 2010, have been used. Large-scale traveling ionospheric disturbances generated during magnetic storms and large-scale wave-like ionospheric disturbances registered during geomagnetically quiet periods are considered. Small-scale ionospheric structures were also observed against a background of large-scale traveling iono-spheric disturbances considered in this study.     

Reduction and interpretation of ionospheric sounding ionograms from extremely low satellite orbits

Previously unknown phenomenon was detected during the ionospheric radiosounding on board the MIR space station when the station was below the F region maximum. The work is devoted to describing the most general properties of this phenomenon in terms in concepts prescribed by the URSI Handbook of ionogram Interpretation and Reduction in order to consider and analyze the phenomenon using the known categories and concepts of this handbook.     

Multiple scattering effects under vertical sounding of equatorial ionosphere

This paper presents a theoretical study of the influence of electron density small-scale irregularities on radio propagation under vertical sounding of the equatorial ionosphere. The sounder is assumed to radiate in the plane perpendicular to geomagnetic field lines. An approximate analytical solution of the equation of radiation energy balance in a plane layer of randomly inhomogeneous plasma has been obtained for this case. Analysis of the results shows that multiple scattering leads to attenuation of signal power and change of the signal arrival angles in the sounder vicinity.     

A new campaign for oblique-incidence ionospheric sounding over Europe and its data application

New systematic oblique ionospheric radio sounding measurements over Central Europe, concerning the radio links between Inskip (UK, 53.5°N, 2.5°W) and Rome (Italy, 41.8°N, 12.5°E) and between Inskip and Chania (Greece, 35.7°N, 24.0°E), have been performed since November 2003.Different long-term (i.e. monthly median) ionospheric predictions and nowcasting techniques have been applied and compared with the oblique-incidence radio sounding measurements.The MUF (basic maximum usable frequency) measurements observed during the early part of the experiment have been used to compare the performances of different methods. The preliminary analysis has shown good performances for the long-term prediction models, in particular in winter months for ICEPAC (ionospheric communications enhanced profile analysis and circuit) and in equinox/summer months for ASAPS (advanced stand-alone prediction system) and SIRM&LKW (simplified ionospheric regional model & lockwood). The nowcasting methods SIRMUP&LKW (SIRM updating method & lockwood) and ISWIRM (instantaneous space weighted ionospheric regional model) reveal good results for moderate and disturbed geomagnetic conditions when compared with the long-term prediction methods.     

Usage of regularization techniques for effective electron collision frequency determination from oblique ionospheric sounding

Computer modelling is used to investigate the possibility of determining ionospheric parameters from slightly oblique ionospheric soundings, using absorption data for decametric radio waves of different polarization. It is shown that with mean square measurement errors of 0.5 dB, and using regularization algorithms to solve the inverse problems, electron collision frequency profiles can be obtained for the night F-region with errors of less than 30%. Both temperatures of electrons and neutrals are also determined to within 10%.     

Determination of the vertical electron-density profile in ionospheric tomography: experimental results

The reconstruction of the vertical electron-density profile is a fundamental problem in ionospheric tomography. Lack of near-horizontal ray paths limits the information available on the vertical profile, so that the resultant image of electron density is biased in a horizontal sense. The vertical profile is of great importance as it affects the authenticity of the entire tomographic image. A new method is described whereby the vertical profile is selected using relative total-electron-content measurements. The new reconstruction process has been developed from modelling studies. A range of background ionospheres, representing many possible peak heights, scale heights and electron densities are formed from a Chapman profile on the bottomside with a range of topside profiles. The iterative reconstruction process is performed on all of these background ionospheres and a numerical selection criterion employed to select the final image. The resulting tomographic images show excellent agreement in electron density when compared with independent verification provided by the EISCAT radar.     

Day-by-day modelling of the ionospheric F2-layer for year 2002

The thermosphere–ionosphere–mesosphere-electrodynamics general circulation model (TIME-GCM) has been run for the year 2002. Its version 1.2 features include day-by-day input of solar irradiance, geomagnetic energy input parameterized by the 3-h Kp index, and global lower boundary conditions from the National Centres for Environmental Prediction (NCEP) data. In addition, it includes tidal forcing from the global-scale wave model (GSWM) and parameterized gravity waves from below. The computed day-by-day values of noon peak electron density NmF2 agree well with ionosonde data for five northern sites and two southern mid-latitude sites, and closely follow the day-by-day modelled concentration ratio of atomic oxygen to molecular nitrogen. Seasonal and hemispheric patterns appear in the model with some, though not full, success. The model's day-to-day patterns show an impressive degree of variability, with simulations of total variability both above and below those observed.     

Correlation of vertical electrical sounding and electrical borehole log data for groundwater exploration

We have correlated the longitudinal unit conductance CL obtained from interpreted vertical electrical sounding data with the formation resistivity R_t and the formation resistivity factor F, obtained by carrying out electrical borehole logging. Interpreted geophysical data of eleven soundings and two electrical borehole log records are used for the analysis. The geophysical data used were acquired in a sedimentary basin. The study area is called Lower Maner Basin located in the province of Andhra Pradesh, India. Vertical electrical soundings were carried out using a Schlumberger configuration with half current electrode separation varying from 600–1000 m. For logging the two boreholes, a Widco logger‐model 3200 PLS was used. True formation resistivity R_t was calculated from a resistivity log. Formation resistivity factor F was also calculated at various depths using R_t values. An appreciable inverse relation exists between the correlated parameters. The borehole resistivity R_t and the formation resistivity factor F decrease with the increase in the longitudinal unit conductance CL. We have shown the use of such a relation in computing borehole resistivity R_t and formation resistivity factor F at sites that posses only vertical electrical sounding data, with a fair degree of accuracy. Validation of the correlation is satisfactory. Scope for updating the correlation is discussed. Significance and applications of the relation for exploration of groundwater, namely to update the vertical electrical sounding data interpretation by translating the vertical electrical sounding data into electrical borehole log parameters, to facilitate correlations studies and to estimate the porosity (φ), permeability (K) and water saturation S_w of water bearing zones are discussed.     

Robust inversion of vertical electrical sounding data using a multiple reweighted least-squares method

The root cause of the instability problem of the least-squares (LS) solution of the resistivity inverse problem is the ill-conditioning of the sensitivity matrix. To circumvent this problem a new LS approach has been investigated in this paper. At each iteration, the sensitivity matrix is weighted in multiple ways generating a set of systems of linear equations. By solving each system, several candidate models are obtained. As a consequence, the space of models is explored in a more extensive and effective way resulting in a more robust and stable LS approach to solving the resistivity inverse problem. This new approach is called the multiple reweighted LS method (MRLS). The problems encountered when using the L ₁- or L ₂-norm are discussed and the advantages of working with the MRLS method are highlighted. A five-layer earth model which generates an ill-conditioned matrix due to equivalence is used to generate a synthetic data set for the Schlumberger configuration. The data are randomly corrupted by noise and then inverted by using L ₂, L ₁ and the MRLS algorithm. The stabilized solutions, even though blurred, could only be obtained by using a heavy ridge regression parameter in L ₂- and L ₁-norms. On the other hand, the MRLS solution is stable without regression factors and is superior and clearer. For a better appraisal the same initial model was used in all cases. The MRLS algorithm is also demonstrated for a field data set: a stable solution is obtained.     

弹性介质中垂直地震剖面有限差分正演

垂直地震剖面法可以通过认识反射和透射过程,深入了解地震波传播特性,又可以改善地表地震资料关于构造、地层和岩性的解释.本文是在基于垂直地震剖面的基本原理基础上,采用高阶交错网格有限差分数值求解二维弹性波方程,然后对常见的层状介质和岩溶介质模型分别进行模拟,根据模型合成了相关的垂直地震剖面记录,期间采用的是完全匹配层法吸收...     

Some aspects of modelling the high-latitude ionospheric convection from Cluster/Edi data

Measurements onboard Cluster satellites are briefly described, which form the base for determining the intensity and direction of the electric field in the magnetosphere. The aim of this paper is to describe (1) the methodology of calculating the potential distribution at the ionospheric level and the results of constructing spatiotemporal convection patterns for different orientations of the IMF vector in the GSM YZ plane; (2) derivation of basic convection patterns (BCPs), which allow to deduce the statistical ionospheric convection pattern at high latitudes for any IMF Bz and By values (statistical convection model) using different sets of independent data; (3) the consequences of enlarging the amount of data used for analysis; (4) the results of potential calculations with various orders of the spherical harmonics describing them; (5) determination of the cross-polar cap potential with different IMF sector widths (α from 45° down to 10°); (6) the results of our trials to determine the contribution of the IMF Bx component to the convection pattern.     

Characteristics of the mid-latitude ionosphere suitable for modelling ionospheric filtration of ULF waves

Summary An approximate method of one-dimensional modelling of the plasma of the Earth's ionosphere is demonstrated for purposes of studying the ionospheric filtration of ULF waves (micropulsations). Apart from the basic local parameters, characterizing the plasma, also derived local characteristics have been defined, i.e. the mass of the so-called effective ion and its effective collision frequency . Drawing on existing empirical models of the mid-latitude ionosphere, vertical profiles (50 km h 1000 km) were determined of the characteristics N_e N_i, v_e, and for the daytime and nighttime mid-latitude ionosphere under low and enhanced solar activity, which can be used to study the ionospheric ULF filter.

---

aa nu uum m¶rt; ¶rt;a ¶rt;uau na ¶rt; u ¶rt; nmm uu u umauu (unau). ¶rt; u mu naamau na n¶rt; mu m aamumuu — aa m. a. mu ua, , u mua amma mu, . a mu nuuu ¶rt; ¶rt;um u u n¶rt; mua nuu (50 h 1000 ) aamumu N_e N_i, v_e, u ¶rt; u u ¶rt;u um nu u u amumu. ¶rt;u nam nu uuu u uma.