地表形变监测的改进相干目标法

如何从雷达干涉时间序列影像中获取更全面的相干目标集合,进行变形时间序列分析是当前研究的难点和热点。本文提出了改进的相干目标法,可获取更为全面且可信度高的相干目标集合,进而提高地表形变监测的时空分辨率和精度。根据雷达影像中同类型地物散射分布相近的特点,采用非参数同分布检验算法提取后向散射特性相近的同质点开展空间非局部滤波,提高干涉图的质量。与此同时,利用多尺度的极大似然条纹频率估计算法分离差分干涉图中的系统性相位,并基于同质点进行自适应相干性估计,获取相干性的平稳估计量,从而获取更多的相干点目标。利用20景TerraSAR-X条带模式时间序列影像,分别利用传统的及改进后的相干目标法对香港填海区域地表形变信息进行时序分析。对试验数据的分析结果表明,本文提出的改进方法在具有稀疏植被的填海区可有效增加相干目标点的提取,得到更为可信的沉降结果。     

利用样本生成方法进行机载多光谱LiDAR数据深度学习分类

机载多光谱LiDAR系统能够快速、准确地获取地物的空间几何和光谱信息,为地物覆盖分类和目标识别提供新的数据源。近年来,基于三维点云的深度学习算法取得了一系列突破性进展,然而直接将不规则的原始点云数据输入深度学习模型进行基于点的分类存在一定的困难。本文提出了一种基于FPS-KNN的样本生成方法,用于基于深度学习的机载多光谱LiDAR数据分类。该方法首先对输入数据进行归一化处理;然后利用最远点采样方法(FPS)和K近邻法(KNN)在输入数据中生成一系列规则大小的训练样本数据集。通过机载多光谱LiDAR数据的试验表明,该方法所生成的样本不仅符合卷积神经网络所要求的输入数据形式,而且能够确保对输入场景的完整覆盖。     

Real-time clock offset prediction with an improved model

The GPS orbit precision of the IGS ultra-rapid predicted (IGU-P) products has been remarkably improved since 2007. However, the satellite clock offsets of the IGU-P products have not shown sufficient high-quality prediction to achieve sub-decimeter precision in real-time precise point positioning (RTPPP), being at the level of 1–3 ns (30–90 cm) RMS in recent years. An improved prediction model for satellite clocks is proposed in order to enhance the precision of predicted clock offsets. First, the proposed prediction model adds a few cyclic terms to absorb the periodic effects, and a time adaptive function is used to adjust the weight of the observation in the prediction model. Second, initial deviations of the predictions are reduced by using a recomputed constant term. The simulation results have shown that the proposed prediction model can give a better performance than the IGU-P clock products and can achieve precision better than 0.55 ns (16.5 cm) in real-time predictions. In addition, the RTPPP method was chosen to test the efficiency of the new model for real-time static and kinematic positioning. The numerical examples using the data set of 140 IGS stations show that the static RTPPP precision based on the proposed clock model has been improved about 22.8 and 41.5 % in the east and height components compared to the IGU-P clock products, while the precisions in the north components are the equal. The kinematic example using three IGS stations shows that the kinematic RTPPP precision based on the proposed clock model has improved about 30, 72 and 44 % in the east, north and height components.     

基于临时相干目标监测非城区地表形变

永久散射体干涉测量技术(PSInSAR)地表形变监测能力受限于稳定散射体的空间分布密度,在PS点稀疏的非城区不再有效。本文基于临时相干目标(temporarily coherent targets,TCT)局部时序高相干性和在非城区广泛分布的特点,提出改进算法以解决该难题。该算法通过顾及季节性周期变化筛选干涉对以保留TCT信息,并利用双阈值联合筛选法提取TCT,采用多次差分挖掘、分离TCT相位,最后反演得到TCT形变速率和高程修正量。利用TCT算法,采用24景Sentinel-1A卫星影像提取了靖边县2014-10-23—2016-05-09期间地表形变信息。通过PSInSAR的对比验证,表明临时相干目标时序分析方法能显著提高非城区监测目标空间分布密度并能有效地监测非城区地表形变。     

基于边缘提取和改进型整体松弛匹配算法的InSAR复图像配准方法

配准精度是InSAR合成孔径雷达干涉成像技术中的重要指标。为获得高精确度的测量结果,提出一种包括概略配准、像素级初配准和亚像素级精配准三个环节的逐级提高精度的InSAR复图像配准方法。利用EnView软件提供的经度和纬度实现概略配准、采用基于多边形结构和边缘提取的像素级初匹配方法大大提高匹配速度。考虑以往的匹配算法都是基于能量图进行并且忽略了整体性,采用基于整体松弛匹配和相位最小二乘匹配相结合的亚像素级精匹配算法减少误匹配率,提高匹配精度。实验结果证明该方法具有良好的性能。     

基于DFT模型的大场景InSAR图像配准

图像配准是实现干涉合成孔径雷达(InSAR)高精度相位提取及地形高程反演的关键,大场景图像的高效高精度配准成为近年高分宽幅InSAR成像应用研究的难点问题之一。由于大场景图像中不同区域偏移量及变化规律差异较大,传统最大相干系数配准方法需多分块及插值处理,面临计算量大且配准精度低等问题。针对此问题,本文提出一种基于DFT模型的大场景InSAR高效高精度图像配准算法。该方法利用最小均方差准则构建InSAR复图像配准的DFT模型,采用四叉树自适应分块及矩阵相乘DFT快速重采样配准方法,实现大场景InSAR图像各子块区域的高效高精度亚像素配准。仿真和实测数据验证本文算法的有效性,结果表明该算法不仅可实现大场景InSAR复图像亚像素级配准,还具有较高的运算效率,其运算效率相对于传统FFT配准方法通常可提升3倍以上。     

北斗B1C信号联合捕获策略

目前对含有导频通道的新信号的捕获研究,主要是设计联合捕获算法,提高功率利用率以提升接收性能,分为等长与非等长相干积分联合算法两类. 本文针对北斗B1C信号,深入分析了三种等长相干积分联合算法的加权问题,并解释了相干联合与差分联合算法的联系. 理论和仿真结果表明,相干联合算法具有更优的性能;进一步,本文结合最优相干积分时间理论给出捕获参数设计方案,对比了不同场景条件下等长与非等长相干积分联合算法的性能,给出了捕获B1C信号的优化策略.      

An approach to GPS clock prediction for real-time PPP during outages of RTS stream

The international GNSS service (IGS) has been providing an open-access real-time service (RTS) since 2013, which allows users to carry out real-time precise point positioning (RT-PPP). As the availability of RTS products is vital for RT-PPP, a disruption in receiving RTS products will be a concern. Currently, the IGS Ultra-rapid (IGU) orbit is accurate enough to be used as an alternative orbit for RTS during RTS outages, while the precision of the IGU predicted clock offsets is far below that of the RTS clock product. The existing clock prediction methods based on received RTS clock data will not work well if the discontinuity arises shortly after the start of the RT-PPP processing due to the lack of RTS clock data to fit the prediction model or to predict clock offsets at a high precision. Even if there is a sufficient amount of RTS clock data available, saving large amounts of RTS clock data would also use processor memory. An alternate approach for GPS clock prediction is proposed. The prediction model, composed of linear polynomial and sinusoidal terms, is similar to those used by the precious methods. The main innovation is the determination of the model coefficients: coefficients of linear and sinusoidal terms are estimated with the epoch-differenced clock offsets from the IGU observed part, while the constant coefficient is computed with the latest RTS clock corrections. There is no need to save the received RTS clock corrections, and clock prediction can be carried out even with only one epoch of RTS data. Evaluation of the proposed method shows that the predicted clock offsets within a short period of prediction time, e.g., 5 min, are slightly worse than RTS clock data. Even when the predicted time reaches up to 1 h, the precision of the predicted clock offsets is still higher than that of IGU predicted clock offsets by about 50%.     

Migration through resolution cell compensation in ISAR imaging

Range-Doppler (RD) processing is widely used in conventional inverse synthetic aperture radar (ISAR) imaging. The unwanted translational motion of moving targets is compensated by envelope alignment and autofocus. For existing ISAR imaging algorithms, the scatterers' migration through resolution cells (MTRC) caused by the rotational motion is usually ignored. With the improvement of resolution or the increase of target size, MTRC cannot be neglected. In this letter, the keystone formatting algorithm developed in SAR is used for the MTRC compensation in ISAR. Before the keystone formatting, coherent processing must be performed on the raw phase history data. An effective approach is proposed for this kind of coherent processing. Numerical examples are provided to demonstrate the performance of the proposed approach.     

Impact of GLONASS pseudorange inter-channel biases on satellite clock corrections

GLONASS carrier phase and pseudorange observations suffer from inter-channel biases (ICBs) because of frequency division multiple access (FDMA). Therefore, we analyze the effect of GLONASS pseudorange inter-channel biases on the GLONASS clock corrections. Different Analysis Centers (AC) eliminate the impact of GLONASS pseudorange ICBs in different ways. This leads to significant differences in the satellite and AC-specific offsets in the GLONASS clock corrections. Satellite and AC-specific offset differences are strongly correlated with frequency. Furthermore, the GLONASS pseudorange ICBs also leads to day-boundary jumps in the GLONASS clock corrections for the same analysis center between adjacent days. This in turn will influence the accuracy of the combined GPS/GLONASS precise point positioning (PPP) at the day-boundary. To solve these problems, a GNSS clock correction combination method based on the Kalman filter is proposed. During the combination, the AC-specific offsets and the satellite and AC-specific offsets can be estimated. The test results show the feasibility and effectiveness of the proposed clock combination method. The combined clock corrections can effectively weaken the influence of clock day-boundary jumps on combined GPS/GLONASS kinematic PPP. Furthermore, these combined clock corrections can improve the accuracy of the combined GPS/GLONASS static PPP single-day solutions when compared to the accuracy of each analysis center alone.     

基于加网算法与算法适应性的半色调图像质量评价方法

根据各种数字加网的特性提出了各自最优的评价方法，并针对原始图像和加网图像在视觉上的不同，利用差别图像的统计特性，提出了一种基于加网算法和算法适应性的半色调图像质量评价方法。     

顾及钟差变化率的GPS卫星钟差预报法

提出了一种基于钟差变化率拟合建模的卫星钟差预报方法。以附加周期项的线性或二次多项式作为基础模型对钟差变化率序列进行拟合,最优估计卫星钟差的趋势项系数,然后直接使用精密定轨得到的相应时刻的卫星钟差计算预报初始时刻的基准项系数,来建立卫星钟差的预报模型。以IGS发布的快速星历(IGR)的卫星钟差为试验数据,对GPS星座中各种型号的所有卫星钟差进行预报。结果表明:本文方法3、6、12与24h的预报精度分别可达0.43、0.58、0.90与1.47ns,相比于传统的基于钟差拟合的预报方法,精度分别提高69.3%、61.8%、50.5%与37.2%;与IGS发布的超快速星历(IGU)的预报钟差相比,钟差精度分别提高15.7%、23.7%、27.4%与34.4%。     

时间序列InSAR监测地表形变

针对相干点目标的时间序列,提出了地表形变InSAR技术监测方法,该方法适用于小数据集分析。并采用郑州地区2007年1月到2010年4月期间的8景ALOS PALSAR数据进行验证分析。研究表明,识别的相干点目标具有大的干涉相干值和小的振幅离差,在时间序列中具有可靠的相位。从误差分析和与ENVISAT PSInSAR结果对比分析表明,该文求得的形变速率标准差在0.34mm/a和5.56mm/a之间,表明提出方法是可靠的。     

Investigation of GPS antenna mean phase centre offsets using a full roving observation strategy

In practice, a relatively simple calibration method of full rotation and antenna swapping techniques can be used to control individual GPS antenna mean phase centre offsets without any ground truth survey. Based on these techniques a new full roving strategy is introduced, which is a generalisation of the full rotation and antenna swapping techniques for estimating all of the three components of the mean phase centre offsets in one processing step. This new technique can be used not only for calibration purposes, but also as an observation strategy for a local high-precision network. In the latter case, the proposed method is similar to the classical geodetic approaches, where the biases are cancelled or estimated by proper observation strategies.     

基于两级格网的LiDAR数据组织与改进坡度滤波

提出一种基于双层格网与改进坡度滤波方法.该方法实现对原始数据的两级格网化,在一级网格中选出地面种子点,在此基础上利用二级网格进行地面点选取,不仅提高了运算效率还可以剔除粗差.在改进坡度滤波算法中,对传统滤波算法进行改进,提出3个坡度阈值,有效克服传统坡度滤波算法在地形起伏较大的地方可能发生的错误.试验结果表明,该算法计...     

全方向自适应动态窗口SAR斑点噪声抑制算法

有效地抑制或消除斑点噪声是SAR图像地学应用的前提，通过基于单视数SAR图像的Speckle统计特性和已发展的空间滤波算法分析。发展了一种改进的全方向动态窗口自适应SAR噪声滤波算法，该算法对处理的每一个像元可按图像边界细节划分为需要的全方向子窗口，利用相对标准差判断滤波窗口及子窗口内斑点噪声及边缘信息的存在情况，可实现滤波窗口大小动态调整和窗口内参加滤波像素的自适应选择，对ERS SAR SLC图像试验结果表明，该算法对单视数SAR图像具有较强的Speckle抑制能力。且可较好地保持图像的纹理边界细节信息，有一定的实用价值。     

SAR图像斑点噪声抑制方法与应用研究

通过详细分析SAR图像的判读和应用斑点噪声的算法,得出:多视处理能有效地平滑噪声,但降低空间分辨率;基于空间域滤波算法能有效地平滑斑点噪声,但不同程度地损失边缘和细节信息;基于变换域的小波多尺度滤波可以较好地保持边缘信息,然而其滤波效果不理想。在此基础上提出利用小波分析技术把两种或两种以上的单个滤波方法进行融合,在有效去除斑点噪声时能够较好地保持边缘、细节和纹理信息。最后初步讨论在实际应用中应根据不同情况和要求选择相应的滤波方法。     

增强型多时相云检测

针对云检测在高亮度地表以及雪覆盖区域存在过度检测的问题,设计了一种不依赖热红外波段的增强型多时相云检测EMTCD(Enhanced Multiple Temporal Cloud Detection)算法。首先,利用云的光谱特征建立单时相云检测规则,并基于云、雪的光谱差异构建了增强型云指数ECI(Enhanced Cloud Index),改进了云、雪的区分能力;其次,以同一区域无云影像为参考,基于ECI指数构建了多时相云检测算法,较好地克服了单时相云检测中高亮度地表、雪和云容易混淆的问题,提高了云检测的精度;最后,选择两个典型区域的Landsat-8 OLI影像,对比分析了不同算法的云检测结果。实验结果表明:ECI指数能够有效区分云、雪,EMTCD方法的平均检测精度达到93.2%,高于Fmask(Function of mask)(81.85%)、MTCD(Multi-Temporal Cloud Detection)(66.14%)和Landsat-8地表反射率产品LaSRC(Landsat-8 Surface Reflectance Code)的云检测结果(86.3%)。因此,本文提出的EMTCD云检测算法能够有效地减少高亮度地表和雪的干扰,实现不依赖热红外波段的高精度云检测。     

Rational function optimization using genetic algorithms

In the absence of either satellite ephemeris information or camera model, rational functions are introduced by many investigators as mathematical model for image to ground coordinate system transformation. The dependency of this method on many ground control points (GCPs), numerical complexity, particularly terms selection, can be regarded as the most known disadvantages of rational functions. This paper presents a mathematical solution to overcome these problems. Genetic algorithms are used as an intelligent method for optimum rational function terms selection. The results from an experimental test carried out over a test field in Iran are presented as utilizing an IKONOS Geo image. Different numbers of GCPs are fed through a variety of genetic algorithms (GAs) with different control parameter settings. Some initial constraints are introduced to make the process stable and fast. The residual errors at independent check points proved that sub-pixel accuracies can be achieved even when only seven and five GCPs are used. GAs could select rational function terms in such a way that numerical problems are avoided without the need to normalize image and ground coordinates.     

倾斜相机式投影的几何解法及其与外心投影的比较

本文根据透视投影的基本原理，给出了关于倾斜相机式投影的几何解法，在此基础上分析了倾斜相机式投影与外心投影的异同，提出了二者比较的一致性条件，并给出了实例验证。