科创中国

有效掩护区是定量研究对星载SAR干扰效能比较简洁的手段.通过定义对星载SAR压制式干扰的有效掩护距离和有效掩护区,并结合雷达干扰统一方程,研究建立了对星载SAR干扰的仿真模型,并根据不同时期SAR所采取的天线,引入二种三维天线增益模型进行了仿真,可以得到不同输入条件下干扰掩护区,仿真结果验证了模型的合理性,有利于定量分析和评估对星载SAR的干扰效能.

SAR图像的空间域压缩多采用矢量量化的方法进行.通常的块自适应矢量量化性能好但计算量较大,而残差矢量量化计算量小却在性能上有劣势.基于此,提出了一种新的基于块自适应残差矢量量化的SAR图像压缩算法.根据SAR幅值图像具有近似瑞利分布的特点对图像先进行基于瑞利分布的块自适应矢量量化,然后利用残差图像数据具有近似高斯分布的特点进行二次块自适应矢量量化.并且在残差矢量量化中进行了按照均方误差排序选择性压缩的改进,在压缩比不变的前提下有效提高了压缩系统性能.多幅图像的实验结果表明,相对传统的块自适应矢量量化和残差矢量量化,该算法在达到较高压缩性能和较低计算资源占用量以及较少存储空间占用上获得了有效的改进.

大相对孔径变焦系统在像差补偿自由度较少的光学补偿式变焦系统中,通常需采用较多的镜片才能完成像差校正,导致系统体积和质量不甚理想。通过合理分配变焦参数,优化变焦系统结构,并进行非球面与衍射面复合叠加设计,完成了一个仅含8片透镜的光学补偿式变焦系统。相对孔径1∶1.8,采用320像素×240像素制冷焦平面探测器,工作波段3μm~5μm,变倍比为5×,实现了30mm/60mm/90mm/150mm四档变焦,冷光阑效率100%。折叠光路后,体积约为210mm×100mm×85mm,结构紧凑,以较少的镜片数辅以机械结构的光学补偿变焦方式有效减轻了整机质量。

随着舰载超视距武器系统的广泛应用,舰载火控雷达的效能对武器系统的影响越来越明显,大气是影响火控雷达作用距离的最主要原因之一,因此研究大气对舰载火控雷达效能的影响很有必要.该文从电磁衰减出发研究了大气对电磁波能量的影响;从电磁折射入手分析了大气对电磁波传播路径的影响.

Many attentions for structural synthesis are paid to planar linkages and parallel mechanisms, while design novel pyramid deployable truss structure(PDTS) of satellite SAR mainly depends on experience of designer. To design novel configuration of PDTS, a two-step topology structure synthesis and analysis approach is proposed. Firstly, a conceptual configuration of PDTS is synthesized. Weighted graph and weighted adjacency matrix are established to realize topological description for PDTS. Graph properties are then summarized to distinguish differentia between PDTS and other type structures. According to graph properties, a procedure for synthesis conceptual configuration of PDTS is presented. Secondly, join relationship of components in a PDTS is analyzed. Kinematic chain and corresponding incidence/adjacency matrix are employed to analyze join relationship of PDTS. Properties and simplified rules of kinematic chain are extracted to construct kinematic chain. A procedure for construction kinematic chain of PDTS is then established. Finally, with this two-step approach all 11 rectangular pyramid deployable structures whose folded state is planar are discovered and their kinematic chains are constructed. Based on synthesis results, a novel deployable support structure for satellite SAR is designed. The proposed research can be applied to obtain some novel PDTSs, which is of great importance to design some novel deployable support structures for satellite SAR antenna.

C3I系统是实现指挥、控制、通信和情报的军事电子综合信息系统,雷达作为系统中的重要组成部分,对C3I系统作战效能的发挥有重要影响.针对雷达对目标探测生成的目标航迹问题,基于航迹质量随着目标距离增加而减小的假设,依据雷达性能确定航迹质量服从指数分布,首先提出了基于雷达烧穿距离的航迹质量评估模型;其次,根据历史航迹数据,依据马尔可夫线性估计理论枸建误差协方差估升矩阵,建立了航迹质量预测模型;由航迹质量是随着航迹误差减少而提高的原则以分段形式建立航迹误差与航迹质量的映鼽由映射表确定航迹质量值;最后通过Mallab进行仿真,保证了模型的有效性.

为了研究地星上行和星地下行激光链路孔径内接收光强信号的典型特征,基于大气湍流理论和位相屏方法,计算了短波和中波红外激光在特定大气相干长度条件下,孔径内接收激光功率与总功率的比值及起伏情况。根据统计结果讨论了上下行大气通道传播特性的差异,结果表明相同外界条件下,直径50 cm孔径内接收的下行激光信号强度大于上行激光信号强度1个数量级以上,其信号的起伏程度也低于上行激光;中等湍流下,下行激光孔径接收光强的概率分布函数服从对数正态分布,最大概率接收功率比与无湍流条件下的功率比值一致,分别为0.42%(1.315μm )和0.26%(3.8μm )。

由于超分辨率图像的重建是典型的不适定问题,因此常引入正则化约束来稳定求解.在正则化方法的基础上,提出了一种针对SAR图像不同区域自适应处理的正则SAR图像超分辨重建新算法.该算法根据图像的邻域一致性测度构造自适应平滑约束项,并定义自适应的p L范数对此项进行度量.同时,构造基于1L范数的梯度逼近范数项,将其加入正则化的重建过程中,进一步提高SAR图像的重建质量.实验结果表明,该算法不仅具有良好的稳健性,而且在较好地重建SAR图像细节信息的同时,有效地抑制了斑点噪声,明显改善了重建SAR图像的质量.

基于自回归(auto-regressive,AR)模型的参数化虚拟孔径合成算法无法应用于灵活的稀疏阵列构型,在单快拍和低信噪比(signal-to-noise ratio,SNR)时对极点个数和位置估计不准.该文提出了基于迭代自适应(iterative adap-tive approach,IAA)的非参数化虚拟孔径合成方法,该方法无需估计极点信息,通过迭代计算虚拟孔径的空间谱并恢复虚拟阵元数据.分析和仿真结果表明:该方法在单快拍和低信噪比条件下比参数化方法具有更好的分辨性能和稳健性,可用于阵元位置随机空缺的情况.

Migrating landbirds are known to follow coast lines and concentrate on peninsulas prior to crossing water bodies, es- pecially during daylight but also at night, creating enhanced potential collision hazards with man-made objects. Knowing where these avian migration "hot-spots" occur in time and space is vital to improve flight safety and inform the spatial planning process (e.g. environmental assessments for offshore windfarms). We developed a simple spatial model to identify avian migration hot- spots in coastal areas based on prevailing migration orientation and coastline features known, from visual and radar observations, to concentrate migrating landbirds around land masses. Regional scale model validation was achieved by combining nocturnal passerine movement data gathered from two tier radar coverage (long-range dual-polarization Doppler weather radar and short- range marine surveillance radar) and standardised bird ringing. Applied on a national scale, the model correctly identified the ten most important Danish coastal hot-spots for spring migrants and predicted the relative numbers of birds that concentrated at each site. These bird numbers corresponded well with historical observational data. Here, we provide a potential framework for the es- tablishment of the first three-dimensional avian airspace sanctuaries, which could contribute to more effective conservation of long-distance migratory birds [Current Zoology 60 (5): 680-691, 2014].