Comparison between Microwave Coherent and Incoherent Scattering Models in Corn Field

[Objective] The aim was to compare and analyze microwave coherent and incoherent scattering models in a corn field. [Method] In the research, based on a coherent scattering model （Stile）, we proposed a coherent scattering model exclusive for corn, in which, physical optics （PO） and infinite-length dielectric cylinder were used to calculate single-scattering matrices of corn leaves and stalks. In addition, coherent components produced from interaction among the scattering mechanisms were also considered and this coherent model was compared with the Michigan Mi- crowave Canopy Scattering （MIMICS） model. The measured data in a corn filed in Gongzhuling in Jilin Province were used as the input parameters of the coherent and incoherent models. We simulated backscattering coefficients of VV and HH po- larization at L and C bands and made a comparison between the simulation results. [Result] The simulation results at L-band were poor, which indicated that we could not find regularity at early growth stage of vegetation. In addition, comparisons be- tween coherent and incoherent scattering models proved that the coherence triggered by the scattering mechanism was small. [Conclusion] In the research, we analyzed differences between coherent and incoherent scattering models with change of incident angle, and further analysis on the differences with change of vegetation and soil needed to be made in future.

Coherent and incoherent internal tides in the southern South China Sea

Coherent and incoherent internal tides(CITs and ICITs) in the southern South China Sea were investigated from two sets of _18-month mooring current records. The CITs were mainly composed of diurnal Q _1, O _1, P _1 and K _1 and semidiurnal M_2. The observed diurnal internal tides(ITs) were more coherent than the semidiurnal constituents. Coherent diurnal variance accounted for approximately 58% of the diurnal motion, whereas semidiurnal tides contained a much smaller fraction(35%) of coherent motion. The ICITs mainly consisted of motion at non-tidal harmonic frequencies around the tidal frequency, and showed clear intermittency. The modal decomposition of CITs and ICITs showed that CITs were dominated by mode-1, whereas mode-1 and higher modes in ICITs signals showed comparable amplitudes. CITs and ICITs accounted for approximately 64% and 36% of the total kinetic energy of internal tides, respectively.

Incoherent control of two classes of finite-level quantum systems

The incoherent control of finite-level quantum systems is investigated. Following a brief introduction to coherent control paradigms in quantum control, a control problem that can not be accomplished using only coherent control is presented. For such a control problem, it is proved that it can be accomplished using incoherent control based on projective measurement and coherent control for two classes of finite-level quantum systems, i.e., eigenstate controllable quantum systems and wavefunction controllable quantum systems.

Dark incoherent spatial solitons in logarithmically saturable nonlinear media

This paper studies numerically the dark incoherent spatial solitons propagating in logarithmically saturable nonlinear media by using a coherent density approach and a split-step Fourier approach for the first time. Under odd and even initial conditions, a soliton triplet and a doublet are obtained respectively for given parameters. Simultaneously, coherence properties associated with the soliton triplet and doublet are discussed. In addition, if the values of the parameters are properly chosen, five and four splittings from the input dark incoherent spatial solitons can also form. Lastly, the grayness of the soliton triplet and that of the doublet are studied, in detail.

Giant Kerr nonlinearity induced by interacting quantum coherences from decays and incoherent pumping

A scheme for generating the giant enhancement of the Kerr nonlinearity in a four-level system with the quantum coherences from the decays and the incoherent pumping is proposed. Compared with that generated in a general four- level system, the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption. By using the numerical results, we show that the remarkable enhancement should be attributed to the interaction of the quantum coherences from the decays and the incoherent pumping.

Incoherent and coherent beam combination for master oscillator/power amplifier system with stimulated Brillouin scattering mirror

In this paper, we studied incoherent and coherent beam combining for the master oscillator/power amplifier （MOPA） system with stimulated Brillouin scattering （SBS） mirror. Optic field intensity distributions in the near and far field are numerically calculated for the two kinds of system. The results show that good beam quality in the far field could be obtained. It provides a theoretical basis for experimental research in the future.

Contribution of Coherent and Incoherent π-Photoproduction Channels to the Spin Asymmetry and the GDH Sum Rule for the Deuteron

An explicit evaluation of the deuteron spin asymmetry and the associated Gerasimov-Drell Hearn （GDH） integral for coherent and incoherent π-photoproduction channels with inclusion of rescattering effects is presented. The helicity-dependent total inclusive photoabsorption cross section on the deuteron and the helicity-dependent semiexclusive channels γd→π± NN and γd→π0X （X = pn or d） are explicitly evaluated up to 1.5 GeV. Our model calculations indicate that convergence of the GDH integral is reached for π-production, while it is not completely reached for π-production. For the sum of 7d → πNN and γd→ π0d contributions to the finite GDH integral by explicit integration up to 1.5 GeV, a value of 249.73μb is obtained. The extracted results are compared with available experimental data from MAMI and ELSA. We find that our predictions fairly well reproduce the data in the μ±NN case, while fail to predict the measured shape of the μ0X channel.

Unsupervised change detection of man-made objects using coherent and incoherent features of multi-temporal SAR images

Constrained by complex imaging mechanism and extraordinary visual appearance,change detection with synthetic aperture radar(SAR)images has been a difficult research topic,especially in urban areas.Although existing studies have extended from bi-temporal data pair to multi-temporal datasets to derive more plentiful information,there are still two problems to be solved in practical applications.First,change indicators constructed from incoherent feature only cannot characterize the change objects accurately.Second,the results of pixel-level methods are usually presented in the form of the noisy binary map,making the spatial change not intuitive and the temporal change of a single pixel meaningless.In this study,we propose an unsupervised man-made objects change detection framework using both coherent and incoherent features derived from multi-temporal SAR images.The coefficients of variation in timeseries incoherent features and the man-made object index(MOI)defined with coherent features are first combined to identify the initial change pixels.Afterwards,an improved spatiotemporal clustering algorithm is developed based on density-based spatial clustering of applications with noise(DBSCAN)and dynamic time warping(DTW),which can transform the initial results into noiseless object-level patches,and take the cluster center as a representative of the man-made object to determine the change pattern of each patch.An experiment with a stack of 10 TerraSAR-X images in Stripmap mode demonstrated that this method is effective in urban scenes and has the potential applicability to wide area change detection.

Dose and dose rate effects on coherent-to-incoherent transition of precipitates upon irradiation

A typical precipitation hardened alloy, Cu-Co dilute alloy was selected to study the precipitation behavior and irradiation effect on precipitates. It is found that the principal effect of ion irradiation on the coherent precipitates is loss of coherency, and TEM cross-section observations show that the fraction of the incoherent precipitates is dependent on dose but not on dose rate during heavy ion irradiation.

Coherent incoherent transition in the spin boson model with a super-ohmic bath

The temperature effect on tunnelling splitting in the spin boson model with a super-ohmic bath is studied by the small polaron theory. The coherent-incoherent transition temperature is calculated and its dependence on dissipation strength and bare tunnelling splitting is analysed. In additional to the traditional transition point described in textbooks, a new kind of transition is found in the low dissipation region, showing different temperature dependence in the transition. The relation to the corresponding transition in the polaron-phonon system is also discussed.

Impact of Interacting Quantum Coherence via Decays and Incoherent Pumping on Transient and Steady-State Behaviors of Absorption

The effects from quantum coherence via decays and incoherent pumping on the lasing without inversion(LWI) are investigated in a four-level system.By analyzing the transient and steady-state behaviors of the absorption,we find that the gain occurs when both spontaneously generated coherence(SGC) and coherence induced by incoherent pumping(IPC) are considered.We attribute the occurrence of the gain to the interaction of quantum coherence via decays and incoherent pumping.

Heat conduction of multilayer nanostructures with consideration of coherent and incoherent phonon transport

We report a theoretical investigation of coherent-to-incoherent heat conduction in multilayer nanostructures.In the coherent regime where the phonon motion is quasi-harmonic,the elastic continuum model gives accurate cross-plane thermal conductivity predictions of upper limits and demonstrates that the coherent transport is the result of the interplay between intrinsic wave effects.As the temperature or system size increases,the phonon dephasing scattering results in the deviation of thermal conductivity from the coherent-limit calculation.By further introducing the incoherence of phonons,we reproduce the classical minimum thermal conductivity,indicating the feasibility of extending the pure wave model into the wave-particle crossing regime.

An improvement of adaptive line enhancer by means of coherent accumulation algorithm

It is well known that the adaptive line enhancer (ALE) is effective detector of CW signal with unknown frequency in the background of white noise. The system processing gain of ALE, when the LMS algorithm is used, however, is not satisfactory because of the presence of iterative noise and weight noise. In this paper, the coherent accumulation algorithm of ALE, called as ALECA, is suggested. It is shown that the adaptive filter employing this new algorithm possesses the ARMA structure. The experimental results also show that the processing gain of ALECA is about 14dB higher than that of conventional ALE.

频率分组编码信号的相参积累算法

针对捷变频信号的相参积累处理进行研究,提出了一种基于频率分组编码信号的相参积累算法。以线性调频(Linear frequency modulation,LFM)信号为基础,构建了频率分组编码信号,使得发射信号的脉冲载频序列具有一定随机性,保证了波形的抗干扰能力。同时针对频率捷变信号相位非相参带来的主瓣展宽和旁瓣抬高问题,设计了对应编码信号的相参处理方法。首先对回波脉压后的信号进行高分辨距离补偿,然后通过速度遍历插值和距离一致性校正实现脉组内相参处理,最后利用编码信号载频序列的优势实现脉组间相参处理。在仿真实验中,对构建的编码信号相较于LFM信号在抗干扰方面的优越性进行了验证,同时验证了所提相参处理方法相较于基于压缩感知的稀疏重构算法的有效性。

一种基于TRT-SKT-HAF的变加速目标快速相参积累算法

在雷达高速机动目标的检测中,目标的运动特性会带来距离走动和多普勒徙动现象,不利于后续进行相参积累。传统算法为解决目标运动造成的影响,需要对目标的运动参数进行搜索,加大了计算量。针对上述问题,文中提出了一种基于慢时间序列反转变换(TRT)-二阶keystone变换(SKT)-高阶模糊函数(HAF)的变加速目标快速相参积累算法。该算法通过TRT和SKT校正距离走动,利用HAF估计目标加速度并构建相位补偿函数以校正多普勒徙动。与广义Radon-Fourier变换相比,所提方法无需进行任何参数搜索,计算复杂度减少了3个数量级。仿真结果表明,所提方法在检测门限上相比于Radon分数阶模糊函数算法降低了5 dB,在低信噪比下有更好的检测性能。

复杂干扰杂波环境下三维目标检测前跟踪算法

针对因随机假目标干扰、强杂波存在的复杂环境中三维目标检测问题,提出一种基于平行线坐标变换的多层次检测前跟踪算法。雷达量测点被先后置于规格化后的径向距离-时间平面、方位角-时间平面和俯仰角-时间平面分层次进行非相参积累和点迹筛选,每次筛选只对上一层的筛选结果进行处理,再根据先验信息进行航迹约束和航迹融合,得到最终检测结果。通过仿真对算法进行性能验证和分析,结果显示,该算法在不同信干杂比、量测误差和杂波密度下均能有效滤除虚假量测点,实现真实航迹的检测。

一种基于相位调制的雷达二次回波抑制方法

二次回波形成的虚假目标影响了雷达对感兴趣目标的探测。采用相位调制的方法首先对雷达发射脉冲信号的相位进行调制,再对回波信号的相位进行校正。由于二次回波调制相位与当前的校正相位存在残差,通过控制该相位残差,使二次回波的能量在多普勒维上均匀分布,从而降低了二次回波被检测概率。该方法同样适用于多次回波,具有一定的工程应用价值。

一种基于波束重置提高测角精度的方法

针对雷达天线转动时波束对回波信号产生调制,导致多脉冲积累雷达比幅测角时测量精度下降的问题,分析了测角精度恶化产生的机理,提出了基于波束重置提高测角精度的方法,并进行了仿真分析和试验验证.仿真和试验结果表明,该方法可行有效;当积累脉冲数较多时,与传统方法相比,本文提出的方法测量精度更高,适用范围更广.

High-Precision DOA Estimation Method Based on Synthetic Aperture Technique

The existing direction-of-arrival(DOA)estimation methods only utilize the current received signals,which are susceptible to noise.In this paper,a method for DOA estimation based on a motion platform is proposed to achieve high-precision DOA estimation by utilizing past and present signals.The concept of synthetic aperture is introduced to construct a linear DOA estima-tion model.A DOA fine-tuning method based on the linear model is proposed to eliminate the lin-ear DOA variation,achieving a non-coherent accumulation of DOA estimations.Moreover,the baseband modulation and the phase modulation caused by the range history are compensated to achieve the coherent accumulation of all the DOA estimations.Simulation results show that the proposed method can significantly improve the DOA estimated accuracy at low signal-to-noise ratios(SNR).

双机频率域交替闪烁的协同相参信号处理方法

多机协同探测从空域方面扩展了雷达辐射波形的复杂度,频率域交替闪烁为空战场强对抗复杂电磁环境下空、时、频域高度隐蔽提供了多维手段。针对双机编队频率域交替闪烁探测模式下距离—多普勒二维相参处理,本文提出了一种交替方向乘子法(ADMM)框架下嵌套多点欠定系统聚焦求解(MFOCUSS)的相位误差估计和二维场景重构方法。仿真结果表明,该方法能够精确估计双机雷达系统频率源引入的固有相位误差,同时对大间隔的双机频率能够进行有效地相参积累和二维场景重构。通过研究,本文设计一种新的双机协同探测工作模式,解决了双机频率域闪烁探测模式下的相位校正和场景重建问题,为复杂电磁环境下协同探测提供了信号处理方法。