太赫兹频段金属和介质粗糙目标的散射特性是研究太赫兹雷达目标特性的重要基础。当目标表面的主曲率半径远远大于入射波长,且粗糙表面高度起伏与斜率起伏远小于入射波长时,根据稳定相位法和标量近似法,可获得粗糙金属和介质目标的相干...太赫兹频段金属和介质粗糙目标的散射特性是研究太赫兹雷达目标特性的重要基础。当目标表面的主曲率半径远远大于入射波长,且粗糙表面高度起伏与斜率起伏远小于入射波长时,根据稳定相位法和标量近似法,可获得粗糙金属和介质目标的相干散射截面和非相干散射截面。基于稳定相位法,任意目标的相干散射截面可退化为粗糙导体、光滑介质和粗糙介质目标的相干散射。该文分析了电大尺寸光滑金属铝和介质白漆球的散射截面,与Mie理论计算的介质球的散射特性吻合,散射截面误差小于0.1 d Bm^2。采用朗伯定理,验证了粗糙介质球的太赫兹非相干散射精确解,当目标表面剖分精度越高,非相干散射的计算精度越高。该文数值计算了粗糙介质球的太赫兹相干和非相干散射特性,分析了表面粗糙度和表面材料对散射特性的影响,为电大尺寸空间目标太赫兹散射特性分析提供了理论基础。展开更多
In this paper,the surfaces are modeled by multiscaled band-limited continuous fractal function and fractional Brownian motion function.The relationship between the scattering behavior and geometrical characteristics o...In this paper,the surfaces are modeled by multiscaled band-limited continuous fractal function and fractional Brownian motion function.The relationship between the scattering behavior and geometrical characteristics of the fractal surface is analysed in detail based on the perturbation solution and Kirchhoff approximation.Finally,some discussions are given about scattering from fractal surface.展开更多
Using high temporal resolution optical data obtained from three-wavelength all-sky imagers at Chinese Yellow River Station in the Arctic, together with the EISCAT Svalbard radar （ESR） and SuperDARN radars, we invest...Using high temporal resolution optical data obtained from three-wavelength all-sky imagers at Chinese Yellow River Station in the Arctic, together with the EISCAT Svalbard radar （ESR） and SuperDARN radars, we investigated the dayside pole- ward moving auroral forms （PMAFs） and the associated plasma features in the polar ionosphere under difibrent interplanetary magnetic field （1MF） conditions, between 0900 and 1010 UT on 22 December 2003. Simultaneous optical and ESR observations revealed that all PMAFs were clearly associated with pulsed particle precipitations. During northward IMF, particles can precipi- tate into lower altitudes and reach the ionospheric E-region, and there is a reverse convection cell associated with these PMAFs. This cell is one of the typical signatures of the dayside high-latitude （lobe） reconnection in the polar ionosphere. These results indicate that the PMAFs were associated with the high-latitude reconnection. During southward IMF, the PMAFs show larger lati- tudinal motion, indicating a longer mean lifetime, and the associated ionospheric features indicate that the PMAFs were generated by the dayside low-latitude reconnection.展开更多
Historic block records the historic development and changes of a city,contains rich cultural resources,and is an important product in the process of urban development.Historic block of Zhongshan Road has a long histor...Historic block records the historic development and changes of a city,contains rich cultural resources,and is an important product in the process of urban development.Historic block of Zhongshan Road has a long history,so there are many historical buildings with local characteristics and traditional style of commercial market,and it is an important window of refl ecting characteristics and regional culture of Quanzhou ancient city.However in long-period development process,historic buildings and blocks in the block along Zhongshan Road of Quanzhou City were destroyed.We initially study how to rationally develop and protect these precious historic and cultural relics,and the methods,principles and countermeasures of protection are put forward.展开更多
The function and physical mechanism of heat flow and the viscous stress in the velocity distribution function expanded by Maxwellian distribution are presented. With the introduction of effective temperature Tf, incoh...The function and physical mechanism of heat flow and the viscous stress in the velocity distribution function expanded by Maxwellian distribution are presented. With the introduction of effective temperature Tf, incoherent scatter spectra from plasma for electromagnetic wave in arbitrary line of sight are given. The effect of asymmetry and anisotropy provided by heat flow and the viscous stress on power spectra is discussed. Radar spectra are calculated for different cases of electric field, direction, collision frequency and temperature. The effect of heat flow and the viscous stress on inversion results is analyzed. With a large electric field, the character of non-Maxwellian must be considered.展开更多
On 12 May 2008 at 14:28 BJT, a great earthquake (M=8.0) occurred in Wenchuan (31.00°N, 103.40°E), China. The hourly foF2 from 5 to 12 May have been analyzed over four ionospheric observatories: Kunming (25.0...On 12 May 2008 at 14:28 BJT, a great earthquake (M=8.0) occurred in Wenchuan (31.00°N, 103.40°E), China. The hourly foF2 from 5 to 12 May have been analyzed over four ionospheric observatories: Kunming (25.00°N, 102.70°E), Chongqing (29.50°N, 106.40°E), Lhasa (29.63°N, 91.17°E), and Lanzhou (36.07°N, 103.87°E). The results show that foF2 were notably abnormal from upper bound (the maximum abnormality up to 65% at 17:00 BJT) and lasted about 3 h on 9 May over Chongqing station. Moreover, there were obvious perturbations of foF2 on the same day over other stations except Lhasa. Taking into account that the solar activity and geomagnetic activity were very quiet during this period, we can conclude that the observed positive ionospheric perturbations were likely associated with the imminent earthquake.展开更多
The electron velocity distribution function and the incoherent scatter spectra during ionospheric heating in low ionosphere region are presented with consideration of the elastic collision between electrons and neural...The electron velocity distribution function and the incoherent scatter spectra during ionospheric heating in low ionosphere region are presented with consideration of the elastic collision between electrons and neural particles and the excitation of rotation energy level. The effects of pump frequency and electric fields on the spectra are discussed. With the increase of electric field, the non-Maxwellian feature is enhanced, and with the increase of heating frequency, the non-Maxwellian feature is weak- ened. The non-Maxwellian factor will bring a large error in ionosphere parameters, which must be con- sidered in the inversion.展开更多
Using high temporal resolution optical data obtained from three-wavelength all-sky imagers over six winters continuously at Yellow River Station （78.92°N,11.93°E） in Arctic,we statistically investigated th...Using high temporal resolution optical data obtained from three-wavelength all-sky imagers over six winters continuously at Yellow River Station （78.92°N,11.93°E） in Arctic,we statistically investigated the dependence of location of poleward moving auroral forms （PMAFs） on the interplanetary magnetic field （IMF） B z and B y components as a function of MLT and MLAT under stable IMF conditions.It is found that more PMAFs occurred in lower latitude for Bz＆lt;0 and there was less evident IMF B y-related prenoon-postnoon asymmetry for Bz＆lt;0 than for Bz＆gt;0.We found that the PMAFs were distributed over a wide range of MLT when Bz＆lt;0,which indicates that the reconnection X-line might spread like an ’S’ shape.However,during northward IMF,PMAFs were observed predominantly prenoon for IMF By＆gt;0 and postnoon for IMF By＆lt;0 associating with the effect of the high-latitude reconnection,which is largely consistent with the theoretical model of the convection flow.展开更多
The surface electric current of the sea surface and the first-order scattering field from the spherical target were obtained by employing Physical Optics method and Mie theory,respectively. The backscattering field of...The surface electric current of the sea surface and the first-order scattering field from the spherical target were obtained by employing Physical Optics method and Mie theory,respectively. The backscattering field of the time-evolving sea surface was calculated by using Kirchhoff Approximation. Meanwhile,by taking the ad-vantage of a newly developed technique that utilizes the reciprocity theorem,the difficulty in formulating the secondary coupling scattering fields from the spherical target above the sea surface was reduced. The dependence of the secondary cou-pling backscattering field on the size and the position of the spherical target was discussed,and the characteristic of the Doppler spectrum of the composite back-scattering field with different incident angles was analyzed in detail.展开更多
In the precise point positioning(PPP),some impossible accurately simulated systematic errors still remained in the GPS observations and will inevitably degrade the precision of zenith tropospheric delay(ZTD) estimatio...In the precise point positioning(PPP),some impossible accurately simulated systematic errors still remained in the GPS observations and will inevitably degrade the precision of zenith tropospheric delay(ZTD) estimation.The stochastic models used in the GPS PPP mode are compared.In this paper,the research results show that the precision of PPP-derived ZTD can be obviously improved through selecting a suitable stochastic model for GPS measurements.Low-elevation observations can cover more troposphere information that can improve the estimation of ZTD.A new stochastic model based on satellite low elevation cosine square is presented.The results show that the stochastic model using satellite elevation-based cosine square function is better than previous stochastic models.展开更多
The extended Huygens-Fresnel principle and Goodman model was utilized for target surface to derive the mutual coherence function(MCF) of a Gaussian beam reflected from an arbitrary rough target in atmospheric turbulen...The extended Huygens-Fresnel principle and Goodman model was utilized for target surface to derive the mutual coherence function(MCF) of a Gaussian beam reflected from an arbitrary rough target in atmospheric turbulence. According to the MCF, expressions of the mean irradiance and average speckle size at the receiver were obtained. The analysis indicated that the mean intensity is closely related to the ratio of root mean square(rms) height to the lateral correlation length. In addition, the speckle size at the receiver is associated with turbulence strength, propagation distance and roughness of the target. The results can be reduced to the result of a Gaussian beam illuminating rough target and scattering from a target in free space.展开更多
Particles swarm optimization（PSO） and differential evolution（DE） algorithms based on optimization are employed to estimate low atmospheric refractivity profiles from radar sea clutter.Low atmospheric refractivity ...Particles swarm optimization（PSO） and differential evolution（DE） algorithms based on optimization are employed to estimate low atmospheric refractivity profiles from radar sea clutter.Low atmospheric refractivity profiles are modeled as evaporation ducts.The objective functions,which are used to evaluate the fit of simulated and measured power in estimation procedures,are also investigated at different frequencies such as L-,S-,C-and X-frequency at 10 m/s wind speeds.The results show that all the objective functions are multi-peak functions.The Adjusted Barton Model of radar cross section（RCS） is adopted.PSO and DE algorithms are compared with genetic algorithm（GA） by 200 Monte Carlo simulation estimations.Simulation results indicate that DE has the best global search ability,and PSO has the highest success probability.According to the statistical results,PSO algorithm with the population size 30 is the appropriate way for evaporation duct estimation.展开更多
Based on the dipole source method, all components of the Green＇s functions in spectral domain are restructured concisely by four basis functions, and in terms of the two-level discrete complex image method （DCIM） w...Based on the dipole source method, all components of the Green＇s functions in spectral domain are restructured concisely by four basis functions, and in terms of the two-level discrete complex image method （DCIM） with the high order Sommerfeld identities, an efficient algorithm for closed-form Green＇s functions in spatial domain in multilayered media is presented. This new work enjoys the advantages of the surface wave pole extraction directly carried out by the generalized integral path without troubles of that all components of Green＇s function in spectral domain should be reformed respectively in transmission line network analogy, and then the Green＇s functions for mixed-potential integral equation （MPIE） analysis in both near-field and far-field in multilayered media are obtained. In addition, the curl operator for coupled field in MPIE is avoided conveniently. It is especially applicable and useful to characterize the electromagnetic scattering by, and radiation in the presence of, the electrically large 3-D objects in multilayered media. The numerical results of the S-parameters of a microstrip periodic bandgap （PBG） filter, the radar cross section （RCS） of a large microstrip antenna array, the characteristics of scattering, and radiation from the three-dimensional （3-D） targets in multilayered media are obtained, to demonstrate better effectiveness and accuracy of this technique.展开更多
文摘太赫兹频段金属和介质粗糙目标的散射特性是研究太赫兹雷达目标特性的重要基础。当目标表面的主曲率半径远远大于入射波长,且粗糙表面高度起伏与斜率起伏远小于入射波长时,根据稳定相位法和标量近似法,可获得粗糙金属和介质目标的相干散射截面和非相干散射截面。基于稳定相位法,任意目标的相干散射截面可退化为粗糙导体、光滑介质和粗糙介质目标的相干散射。该文分析了电大尺寸光滑金属铝和介质白漆球的散射截面,与Mie理论计算的介质球的散射特性吻合,散射截面误差小于0.1 d Bm^2。采用朗伯定理,验证了粗糙介质球的太赫兹非相干散射精确解,当目标表面剖分精度越高,非相干散射的计算精度越高。该文数值计算了粗糙介质球的太赫兹相干和非相干散射特性,分析了表面粗糙度和表面材料对散射特性的影响,为电大尺寸空间目标太赫兹散射特性分析提供了理论基础。
文摘In this paper,the surfaces are modeled by multiscaled band-limited continuous fractal function and fractional Brownian motion function.The relationship between the scattering behavior and geometrical characteristics of the fractal surface is analysed in detail based on the perturbation solution and Kirchhoff approximation.Finally,some discussions are given about scattering from fractal surface.
基金supported by the National Natural Science Foundation of China (Grant nos. 40974083, 41031064, 41104091,41104090, 41274149 and 41274164)the Ocean Public Welfare Scientific Research Project of China (Grant no. 201005017)+1 种基金the Polar Strategic Research Foundation of China (Grant nos. 20100202, 20100203 and 20120304)the Polar Environment Comprehensive Investigation & Assessment Programs(Grant no. CHINARE 2012-02-03)
文摘Using high temporal resolution optical data obtained from three-wavelength all-sky imagers at Chinese Yellow River Station in the Arctic, together with the EISCAT Svalbard radar （ESR） and SuperDARN radars, we investigated the dayside pole- ward moving auroral forms （PMAFs） and the associated plasma features in the polar ionosphere under difibrent interplanetary magnetic field （1MF） conditions, between 0900 and 1010 UT on 22 December 2003. Simultaneous optical and ESR observations revealed that all PMAFs were clearly associated with pulsed particle precipitations. During northward IMF, particles can precipi- tate into lower altitudes and reach the ionospheric E-region, and there is a reverse convection cell associated with these PMAFs. This cell is one of the typical signatures of the dayside high-latitude （lobe） reconnection in the polar ionosphere. These results indicate that the PMAFs were associated with the high-latitude reconnection. During southward IMF, the PMAFs show larger lati- tudinal motion, indicating a longer mean lifetime, and the associated ionospheric features indicate that the PMAFs were generated by the dayside low-latitude reconnection.
文摘Historic block records the historic development and changes of a city,contains rich cultural resources,and is an important product in the process of urban development.Historic block of Zhongshan Road has a long history,so there are many historical buildings with local characteristics and traditional style of commercial market,and it is an important window of refl ecting characteristics and regional culture of Quanzhou ancient city.However in long-period development process,historic buildings and blocks in the block along Zhongshan Road of Quanzhou City were destroyed.We initially study how to rationally develop and protect these precious historic and cultural relics,and the methods,principles and countermeasures of protection are put forward.
基金the National Natural Science Foundation of China (Grant No. 40310223)
文摘The function and physical mechanism of heat flow and the viscous stress in the velocity distribution function expanded by Maxwellian distribution are presented. With the introduction of effective temperature Tf, incoherent scatter spectra from plasma for electromagnetic wave in arbitrary line of sight are given. The effect of asymmetry and anisotropy provided by heat flow and the viscous stress on power spectra is discussed. Radar spectra are calculated for different cases of electric field, direction, collision frequency and temperature. The effect of heat flow and the viscous stress on inversion results is analyzed. With a large electric field, the character of non-Maxwellian must be considered.
基金supported by the Seismic Public Welfare Scientific Research Special Appropriation Project of China (Grant No.201008007)National Key Technology R & D Program (Grant No.2006BAB18B06)National Defense Foundation of China (Grant No.H312009C001)
文摘On 12 May 2008 at 14:28 BJT, a great earthquake (M=8.0) occurred in Wenchuan (31.00°N, 103.40°E), China. The hourly foF2 from 5 to 12 May have been analyzed over four ionospheric observatories: Kunming (25.00°N, 102.70°E), Chongqing (29.50°N, 106.40°E), Lhasa (29.63°N, 91.17°E), and Lanzhou (36.07°N, 103.87°E). The results show that foF2 were notably abnormal from upper bound (the maximum abnormality up to 65% at 17:00 BJT) and lasted about 3 h on 9 May over Chongqing station. Moreover, there were obvious perturbations of foF2 on the same day over other stations except Lhasa. Taking into account that the solar activity and geomagnetic activity were very quiet during this period, we can conclude that the observed positive ionospheric perturbations were likely associated with the imminent earthquake.
基金Supported by the National Natural Science Foundation of China (Grant No. 40310223)the National Key Laboratory of Electromagnetic Environment (LEME)National Key Technologies R&D Program of China (Grant No. 2006BAB18B06)
文摘The electron velocity distribution function and the incoherent scatter spectra during ionospheric heating in low ionosphere region are presented with consideration of the elastic collision between electrons and neural particles and the excitation of rotation energy level. The effects of pump frequency and electric fields on the spectra are discussed. With the increase of electric field, the non-Maxwellian feature is enhanced, and with the increase of heating frequency, the non-Maxwellian feature is weak- ened. The non-Maxwellian factor will bring a large error in ionosphere parameters, which must be con- sidered in the inversion.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41031064,40974103,40974083,40904041,40890164,41104091,and 41104090)the Polar Strategic Research Foundation of China (Grant No. 20120304)the Ocean Public Welfare Scientific Research Project,State Oceanic Administration of the People's Republic of China (Grant No. 201005017)
文摘Using high temporal resolution optical data obtained from three-wavelength all-sky imagers over six winters continuously at Yellow River Station （78.92°N,11.93°E） in Arctic,we statistically investigated the dependence of location of poleward moving auroral forms （PMAFs） on the interplanetary magnetic field （IMF） B z and B y components as a function of MLT and MLAT under stable IMF conditions.It is found that more PMAFs occurred in lower latitude for Bz＆lt;0 and there was less evident IMF B y-related prenoon-postnoon asymmetry for Bz＆lt;0 than for Bz＆gt;0.We found that the PMAFs were distributed over a wide range of MLT when Bz＆lt;0,which indicates that the reconnection X-line might spread like an ’S’ shape.However,during northward IMF,PMAFs were observed predominantly prenoon for IMF By＆gt;0 and postnoon for IMF By＆lt;0 associating with the effect of the high-latitude reconnection,which is largely consistent with the theoretical model of the convection flow.
基金the National Natural Science Foundation of China (Grant No. 60571058)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20070701010)
文摘The surface electric current of the sea surface and the first-order scattering field from the spherical target were obtained by employing Physical Optics method and Mie theory,respectively. The backscattering field of the time-evolving sea surface was calculated by using Kirchhoff Approximation. Meanwhile,by taking the ad-vantage of a newly developed technique that utilizes the reciprocity theorem,the difficulty in formulating the secondary coupling scattering fields from the spherical target above the sea surface was reduced. The dependence of the secondary cou-pling backscattering field on the size and the position of the spherical target was discussed,and the characteristic of the Doppler spectrum of the composite back-scattering field with different incident angles was analyzed in detail.
文摘In the precise point positioning(PPP),some impossible accurately simulated systematic errors still remained in the GPS observations and will inevitably degrade the precision of zenith tropospheric delay(ZTD) estimation.The stochastic models used in the GPS PPP mode are compared.In this paper,the research results show that the precision of PPP-derived ZTD can be obviously improved through selecting a suitable stochastic model for GPS measurements.Low-elevation observations can cover more troposphere information that can improve the estimation of ZTD.A new stochastic model based on satellite low elevation cosine square is presented.The results show that the stochastic model using satellite elevation-based cosine square function is better than previous stochastic models.
基金supported by the National Natural Science Foundation of China(Grant Nos.61172031,61271110 and 61102018)the New Scientific and Technological Star of Shaanxi Province Funded Project(Grant No.2011KJXX39)the Natural Science Foundation of Shaanxi Province education office,China(Grant No.12Jk0955)
文摘The extended Huygens-Fresnel principle and Goodman model was utilized for target surface to derive the mutual coherence function(MCF) of a Gaussian beam reflected from an arbitrary rough target in atmospheric turbulence. According to the MCF, expressions of the mean irradiance and average speckle size at the receiver were obtained. The analysis indicated that the mean intensity is closely related to the ratio of root mean square(rms) height to the lateral correlation length. In addition, the speckle size at the receiver is associated with turbulence strength, propagation distance and roughness of the target. The results can be reduced to the result of a Gaussian beam illuminating rough target and scattering from a target in free space.
基金Supported by the National Natural Science Foundation of China (60771038)the National Key Laboratory of Electromagnetic Environment Foundation of China (9140C0802050703)
文摘Particles swarm optimization（PSO） and differential evolution（DE） algorithms based on optimization are employed to estimate low atmospheric refractivity profiles from radar sea clutter.Low atmospheric refractivity profiles are modeled as evaporation ducts.The objective functions,which are used to evaluate the fit of simulated and measured power in estimation procedures,are also investigated at different frequencies such as L-,S-,C-and X-frequency at 10 m/s wind speeds.The results show that all the objective functions are multi-peak functions.The Adjusted Barton Model of radar cross section（RCS） is adopted.PSO and DE algorithms are compared with genetic algorithm（GA） by 200 Monte Carlo simulation estimations.Simulation results indicate that DE has the best global search ability,and PSO has the highest success probability.According to the statistical results,PSO algorithm with the population size 30 is the appropriate way for evaporation duct estimation.
基金the National Natural Science Foundation of China (Grant No. 60371020)National Defense Pre-research Foundation of China (Grant No. 9140a03020206dz0112)
文摘Based on the dipole source method, all components of the Green＇s functions in spectral domain are restructured concisely by four basis functions, and in terms of the two-level discrete complex image method （DCIM） with the high order Sommerfeld identities, an efficient algorithm for closed-form Green＇s functions in spatial domain in multilayered media is presented. This new work enjoys the advantages of the surface wave pole extraction directly carried out by the generalized integral path without troubles of that all components of Green＇s function in spectral domain should be reformed respectively in transmission line network analogy, and then the Green＇s functions for mixed-potential integral equation （MPIE） analysis in both near-field and far-field in multilayered media are obtained. In addition, the curl operator for coupled field in MPIE is avoided conveniently. It is especially applicable and useful to characterize the electromagnetic scattering by, and radiation in the presence of, the electrically large 3-D objects in multilayered media. The numerical results of the S-parameters of a microstrip periodic bandgap （PBG） filter, the radar cross section （RCS） of a large microstrip antenna array, the characteristics of scattering, and radiation from the three-dimensional （3-D） targets in multilayered media are obtained, to demonstrate better effectiveness and accuracy of this technique.
