Optimal speckle reduction in polarimetric SAR imagery

Speckle is a major cause of degradation in synthetic aperture radar (SAR) imagery. With the availability of fully polarimetric SAR data, it is possible to use the three complex elements (HH, HV, VV) of the polarimetric scattering matrix to reduce speckle. The optimal method for combining the elements of the scattering matrix to minimize image speckle is derived, and the solution is shown to be a polarimetric whitening filter (PWF). A simulation of spatially correlated, K-distributed, fully polarimetric clutter is then used to compare the PWF with other, suboptimal speckle-reduction methods. Target detection performance of the PWF, span, and single-channel |HH|² detectors is compared with that of the optimal polarimetric detector (OPD). A novel, constant-false-alarm-rate (CFAR) detector (the adaptive PWF) is as a simple alternative to the OPD for detecting targets in clutter. This algorithm estimates the polarization covariance of the clutter, uses the covariance to construct the minimum-speckle image, and then tests for the presence of a target. An exact theoretical analysis of the adaptive PWF is presented; the algorithm is shown to have detection performance comparable with that of the OPD     

基于双响应波段工作的红外热像仪测温原理与误差分析

为了提高红外热像仪测温的准确性,根据红外辐射理论,从红外热像仪的测温原理出发,分析了基于双响应工作波段的热像仪的测温原理,得出了目标物体的发射率、物体温度计算公式以及相应误差的估算公式,分析了各影响因素对热像仪测量准确度的影响,提供了一种目标物体发射率的测定方法,对利用红外热像仪准确测量内燃机等热能机械表面温度具有重要的意义。     

Two magnetars: SGR 1627–41 and 1E 1547–5408

We describe the results obtained with Target of Opportunity observations of the galactic sources SGR 1627–41 and 1E 1547–5408. These two transients show several similarities supporting the interpretation of Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters as a single class of strongly magnetized neutron stars.     

Coronal radio-sounding detection of a CME during the 1997 Galileo solar conjunction

Frequency fluctuations of the Galileo S-band radio signal were recorded nearly continuously during the spacecraft’s solar conjunction from December 1996 to February 1997. A strong propagating disturbance, most probably associated with a coronal mass ejection (CME), was detected on 7 February when the radio ray path proximate point was on the west solar limb at about 54 solar radii from the Sun. The CME passage through the line of sight is characterized by a significant increase in the fluctuation intensity of the recorded frequency and by an increase in the plasma speed from about 234 km s⁻¹ up to about 755 km s⁻¹. These velocity estimates are obtained from a correlation analysis of frequency fluctuations recorded simultaneously at two widely-separated ground stations. The density turbulence power spectrum is found to steepen behind the CME front. The Galileo radio-sounding data are compared with SOHO/LASCO observations of the CME in the corona and with WIND spacecraft data near the Earth’s orbit.     

改进PASTd算法在大型自适应阵中的应用

矩阵特征分解算法中紧缩近似投影子空间跟踪(PASTd)算法在自适应阵波束形成中得到了广泛应用.在对其仿真中发现仅在信噪比较低时该算法才能得到较好的结果.针对这一缺陷,正交近似投影子空间跟踪(OPAST)算法被引伸到PASTd中.改进算法可在不知道信号维数的情况下估算信号的特征向量与特征值,并保证特征向量的正交性,因此具有更好的收敛性能,而算法复杂度基本不变.改进算法与多重信号分类(MUSIC)算法相结合应用于大型自适应阵,可对主瓣及其附近区域的干扰进行抑制,并大大降低MUSIC算法的计算量,对其干扰零点的形成有很强实用价值.     

应力波天平在国内激波风洞上的应用

介绍了应力波天平的特点、原理,通过应力波天平设计、制作、校准、试验、数据处理等方面在中国空气动力研究与发展中心φ0.6m激波风洞上的应用情况,指出有必要在国内激波风洞上更进一步地开展应力波天平测力技术.     

Optimization of a tool kit for machining by methods of graph theory

Some methods of optimizing a cutting tool kit by the minimum labour content criterion in milling of an article are considered. Their advantages and disadvantages are given.     

Sharp boundaries of solar wind plasma structures and their relationship to solar wind turbulence

Sharp (<10 min) and large (>20%) solar wind ion flux changes are common phenomena in turbulent solar wind plasma. These changes are the boundaries of small- and middle-scale solar wind plasma structures which can have a significant influence on Earth’s magnetosphere. These solar wind ion flux changes are typically accompanied by only a small change in the bulk solar wind velocity, hence, the flux changes are driven mainly by plasma density variations. We show that these events occur more frequently in high-density solar wind. A characteristic of solar wind turbulence, intermittency, is determined for time periods with and without these flux changes. The probability distribution functions (PDF) of solar wind ion flux variations for different time scales are calculated for each of these periods and compared. For large time scales, the PDFs are Gaussian for both data sets. For small time scales, the PDFs from both data set are more flat than Gaussian, but the degree of flatness is much larger for the data near the sharp flux change boundaries.