相对反射深度的秦皇岛海域叶绿素浓度反演

海水中的叶绿素浓度是描述海洋初级生产力、获知浮游植物丰度及变化规律、评估环境质量、预报生态灾害的主要参数.国内外卫星遥感叶绿素产品的通用反演模型是利用不同波段上遥感反射光谱的强度比值来构建的OC x(x=2～6)算法,应用在一类水体中,全球尺度上的平均相对误差在35％ 左右.但对于固有光学特性复杂且具有较大区域差异性的...     

基于压缩感知理论的大规模MIMO系统下行信道估计中的导频优化理论分析与算法设计

针对大规模多输入多输出(multiple input multiple output, MIMO)系统信道估计中的导频设计问题,在压缩感知理论框架下,提出了一种基于信道重构错误率最小化的自适应自相关矩阵缩减参数导频优化算法.首先以信道重构错误率最小化为目标,推导了正交匹配追踪(orthogonal matching pursuit, OMP)算法下信道重构错误率与导频矩阵列相关性之间的关系,并得出优化导频矩阵的两点准则,即导频矩阵列相关性期望和方差最小化;然后研究了优化导频矩阵的方法,并提出相应的自适应自相关矩阵缩减参数导频矩阵优化算法,即在每次迭代过程中,以待优化矩阵平均列相关程度是否减小作为判断条件,调整自相关矩阵缩减参数值,使参数不断趋近于理论最优.仿真结果表明,与采用Gaussian矩阵、Elad方法、低幂平均列相关方法得到的导频矩阵相比,本文所提方法具有更好的列相关性,且具有更低的信道重构错误率.     

Lu_(2)O_(3)∶Er^(3+)/Yb^(3+)荧光材料的上转换发光及其温度传感特性EI北大核心CSCD

采用CO_(2)激光区熔法制备了Lu_(2)O_(3)∶0.5%Er^(3+)/x%Yb^(3+)(x=1,3,5)上转换荧光材料。X射线衍射结果表明,所制备的Lu_(2)O_(3)∶Er^(3+)/Yb^(3+)荧光材料具有纯Lu_(2)O_(3)晶相。在980 nm激光激发下,样品发出明亮的上转换荧光。光谱测试结果表明,样品上转换荧光强度和荧光中绿光与红光比例随Yb^(3+)离子浓度改变,当Er^(3+)和Yb^(3+)离子浓度分别为0.5%和3%时,样品上转换荧光强度最强。通过荧光强度比(FIR)技术研究了样品Lu_(2)O_(3)∶0.5%Er^(3+)/3%Yb^(3+)在298~873 K温度范围内上转换荧光温度传感特性,在532.8 K时最大绝对灵敏度为0.0060 K^(-1),在298 K时最大相对灵敏度为0.0090 K^(-1)。结果表明,Lu_(2)O_(3)∶Er^(3+)/Yb^(3+)荧光材料非常适合用于宽温度范围荧光温度传感。     

Iterative filtered ghost imaging

It is generally believed that, in ghost imaging, there has to be a compromise between resolution and visibility. Here we propose and demonstrate an iterative filtered ghost imaging scheme whereby a super-resolution image of a grayscale object is achieved, while at the same time the signal-to-noise ratio (SNR) and visibility are greatly improved, without adding complexity. The dependence of the SNR, visibility, and resolution on the number of iterations is also investigated and discussed. Moreover, with the use of compressed sensing the sampling number can be reduced to less than 1% of the Nyquist limit, while maintaining image quality with a resolution that can exceed the Rayleigh diffraction bound by more than a factor of 10.     

Learnable three-dimensional Gabor convolutional network with global affinity attention for hyperspectral image classification

Benefiting from the development of hyperspectral imaging technology, hyperspectral image (HSI) classification has become a valuable direction in remote sensing image processing. Recently, researchers have found a connection between convolutional neural networks (CNNs) and Gabor filters. Therefore, some Gabor-based CNN methods have been proposed for HSI classification. However, most Gabor-based CNN methods still manually generate Gabor filters whose parameters are empirically set and remain unchanged during the CNN learning process. Moreover, these methods require patch cubes as network inputs. Such patch cubes may contain interference pixels, which will negatively affect the classification results. To address these problems, in this paper, we propose a learnable three-dimensional (3D) Gabor convolutional network with global affinity attention for HSI classification. More precisely, the learnable 3D Gabor convolution kernel is constructed by the 3D Gabor filter, which can be learned and updated during the training process. Furthermore, spatial and spectral global affinity attention modules are introduced to capture more discriminative features between spatial locations and spectral bands in the patch cube, thus alleviating the interfering pixels problem. Experimental results on three well-known HSI datasets (including two natural crop scenarios and one urban scenario) have demonstrated that the proposed network can achieve powerful classification performance and outperforms widely used machine-learning-based and deep-learning-based methods.     

内陆水体叶绿素a含量定量检测的研究

以武汉东湖为实验基地,通过对其水体的多次检测,获得了从2006年6月到9月4个月的东湖水体透射光谱,并与蒸馏水透射光谱进行比较,对东湖水富营养化程度进行了定性分析.采用一种新的测量方法得到叶绿素a浓度与677 nm和703 nm处相对强度的差值和比值有很好的线性相关性,建立了东湖水体叶绿素a含量的准确定量检测模型,为实现对东湖水实时、快速、准确监测提供了基础,为高精度遥感水质分析提供了参考.     

基于线阵InGaAs光电二极管阵列的光纤光栅传感解调

采用线阵InGaAs光电二极管阵列和体相位光栅并结合空分复用和波分复用技术,对光纤光栅传感进行解调.设计了基于线阵InGaAs光电二极管阵列和体相位光栅的光纤光栅传感解调系统,通过系统测试和性能分析,该解调系统解调带宽42 nm,信噪比30 dB,波长偏移测量精确度±15 pm,功率测量精确度为±0.3 dB.基于线阵InGaAs光电二极管阵列和体相位光栅的光纤光栅解调系统不但尺寸小,功耗低,而且具有较高的解调速度.     

一种线性相位反演波前测量方法的实验研究

 描述了基于线性相位反演算法的波前传感器的基本组成结构。在实验室内搭建了相应的演示验证实验装置,对该种新型波前测量方法的特性进行了实验研究。实验计算结果表明：这种根据入射全孔径远场光斑强度分布直接反演出入射波前相位的线性相位反演新方法原理是可行的。只需实时测量一幅焦平面图像,根据焦平面上光强分布的微小变化量与入射孔径面上的相位分布的微小变化量之间存在的近似线性关系,就可以用模式复原的原理复原出入射波前相位。传感器对于离焦,像散等像差模式都可以进行较为准确的测量,误差率都小于1。对称系统像差中存在少量的非对称像差对复原结果的准确性影响不大。     

光纤光栅传感器的理论、设计及应用的最新进展

从单参数、多参数及分布式传感的角度,分析了各种光纤光栅传感器的理论及技术发展,详细阐述了光纤光栅敏化与封装技术,论述了光纤光栅传感器的设计方法和实现技术,介绍和评述了光纤光栅器及其传感网络系统应用的最新进展。     

Wavelet-based edge correlation incorporated iterative reconstruction for undersampled MRI

Undersampling k-space is an effective way to decrease acquisition time for MRI. However, aliasing artifacts introduced by undersampling may blur the edges of magnetic resonance images, which often contain important information for clinical diagnosis. Moreover, k-space data is often contaminated by the noise signals of unknown intensity. To better preserve the edge features while suppressing the aliasing artifacts and noises, we present a new wavelet-based algorithm for undersampled MRI reconstruction. The algorithm solves the image reconstruction as a standard optimization problem including a ?₂ data fidelity term and ?₁ sparsity regularization term. Rather than manually setting the regularization parameter for the ?₁ term, which is directly related to the threshold, an automatic estimated threshold adaptive to noise intensity is introduced in our proposed algorithm. In addition, a prior matrix based on edge correlation in wavelet domain is incorporated into the regularization term. Compared with nonlinear conjugate gradient descent algorithm, iterative shrinkage/thresholding algorithm, fast iterative soft-thresholding algorithm and the iterative thresholding algorithm using exponentially decreasing threshold, the proposed algorithm yields reconstructions with better edge recovery and noise suppression.