基于城区航空影像的变化检测

提出一种城区人工地物变化检测方法。其基本思想是:首先利用较简单方法进行变化检测,所检测出的变化都作为待选的变化;然后进行进一步的分析比较,从这些待选的变化中找出我们感兴趣的人工地物的变化。实验结果证明了该方法的有效性和可靠性。     

Improved relativistic transformations in GPS

For GPS satellite clocks, a nominal (hardware) frequency offset and a conventional periodic relativistic correction derived as a dot product of the satellite position and velocity vectors, are used to compensate the relativistic effects. The conventional hardware clock rate offset of 38,575.008 ns/day corresponds to a nominal orbit semi-major axis of about 26,561,400 m. For some of the GPS satellites, the departures from the nominal semi-major axis can cause an apparent clock rate up to 10 ns/day. GPS orbit perturbations, together with the earth gravity field oblateness, which is largely responsible for the orbit perturbations, cause the standard GPS relativistic transformations to depart from the rigorous relativity transformation by up to 0.2 ns/day. In addition, the conventional periodic relativistic correction exhibits periodic errors with amplitudes of about 0.1 and 0.2 ns, with periods of about 6 h and 14 days, respectively. Using an analytical integration of the gravity oblateness term (J₂), a simple analytical approximation was derived for the apparent clock rate and the 6-h periodic errors of the standard GPS gravity correction. For daily linear representations of GPS satellite clocks, the improved relativistic formula was found to agree with the precise numerical integration of the GPS relativistic effects within about 0.015 ns. For most of the Block IIR satellites, the 6-h periodical errors of the GPS conventional relativistic correction are already detectable in the recent IGS final clock combinations.     

Detecting patterns of climate change in long-term forecasts of marine environmental parameters

ABSTRACT

Forecasting environmental parameters in the distant future requires complex modelling and large computational resources. Due to the sensitivity and complexity of forecast models, long-term parameter forecasts (e.g. up to 2100) are uncommon and only produced by a few organisations, in heterogeneous formats and based on different assumptions of greenhouse gases emissions. However, data mining techniques can be used to coerce the data to a uniform time and spatial representation, which facilitates their use in many applications. In this paper, streams of big data coming from AquaMaps and NASA collections of 126 long-term forecasts of nine types of environmental parameters are processed through a cloud computing platform in order to (i) standardise and harmonise the data representations, (ii) produce intermediate scenarios and new informative parameters, and (iii) align all sets on a common time and spatial resolution. Time series cross-correlation applied to these aligned datasets reveals patterns of climate change and similarities between parameter trends in 10 marine areas. Our results highlight that (i) the Mediterranean Sea may have a standalone ‘response’ to climate change with respect to other areas, (ii) the Poles are most representative of global forecasted change, and (iii) the trends are generally alarming for most oceans.     

震前电离层TEC异常探测方法的研究进展

介绍了震前电离层TEC异常探测原理的研究进展和主要的异常探测方法,详细介绍了时间序列法、Kalman滤波和小波变换在电离层异常探测中的原理和应用,总结了传统方法和新方法在电离层异常探测的应用发展情况,并分析了每种方法的优势与不足。为未来中国采用电离层异常探测开展地震预测工作提出了建议。     

结合图像增强和恢复的增强现实跟踪注册

增强现实中的跟踪注册技术一直是研究的重点和难点,而地下矿道和巷道内亮度低,产生的图像较昏暗,车载相机快速运动和抖动,对传统的基于特征匹配的跟踪注册提出了挑战。本文从提高增强现实中跟踪注册稳健性和精度出发,采用基于Retinex改进的方法增强昏暗图像的亮度,同时利用基于对抗神经网络的方法恢复运动模糊图像。首先提取图像ORB特征,实现初始化;然后根据跟踪特征点的数量,开启图像增强和图像恢复线程,提高特征点提取质量和数量。在数据集和真实模拟场景下的试验结果显示,跟踪精度提高了12%左右,在低亮度和含有轻微模糊的情况下,跟踪注册稳健性也有显著提高。     

应用于SAR图像配准的自适应SIFT特征均匀分布算法

SAR图像配准要求提取出稳定且分布均匀的同名点,但是传统的SIFT算法没有考虑特征点的空间分布情况,提取的特征呈块状分布。针对SAR图像数据的特点,提出了一种自适应控制SIFT特征均匀分布算法,利用局部纹理特征,并结合最优化筛选策略,在保证特征点稳定性和准确性的同时,自适应控制特征在不同空间的分布情况,实现SIFT特征点在图像空间和尺度空间的合理分布。最后从提取效率、匹配正确率和分布质量等方面进行对比试验,验证了算法应用于SAR图像配准的能力。     

基于卡尔曼滤波的GPS高动态载波跟踪环路设计

针对高动态环境会使接收机接收信号载频上产生很大的多普勒频移及其变化率,普通的GPS载波跟踪环无法保证可靠的跟踪等问题,通过综合分析传统的二阶叉积自动频率控制环(CPAFC)辅助三阶锁相环(PLL)的高动态载波跟踪环路,以及卡尔曼滤波器在动态跟踪中的优势与劣势,该文设计了一种基于卡尔曼滤波的二阶CPAFC辅助三阶PLL的GPS高动态载波跟踪环路。通过仿真分析证明,新的环路能更好地适应动态性,整体跟踪性能更好;并且在信噪比较低的情况下,环路优势更明显。     

博尔塔拉蒙古自治州植被覆盖度估算

针对传统植被覆盖度估算方法只能估算高密度覆盖的绿色光合植被的问题,该文提出了一种可进行绿色光合植被、非绿色光合植被和裸地覆盖度估算的方法,选取博尔塔拉蒙古自治州2010年和2016年的LandsatTM/OLI影像,通过构建NDVI-DFI特征空间提取端元特征值,运用像元三分模型估算,并与像元二分模型估算结果和实地采样估算结果对比。结果表明:像元三分模型估算与实际情况相符,且精度较好。2016年博州地区植被覆盖度较2010年增长显著,生态环境得到明显改善。像元三分模型能够较好地估算光合/非光合植被覆盖度,提高遥感获取植被信息的能力,为科学评估生态环境质量提供参考。     

Detection of spatio-temporal evolutions on multi-annual satellite image time series: A clustering based approach

The expansion of satellite technologies makes remote sensing data abundantly available. While the access to such data is no longer an issue, the analysis of this kind of data is still challenging and time consuming. In this paper, we present an object-oriented methodology designed to handle multi-annual Satellite Image Time Series (SITS). This method has the objective to automatically analyse a SITS to depict and characterize the dynamic of the areas (the way that the land cover of the areas evolve over time). First, it identifies the spatio-temporal entities (reference objects) to be tracked. Second, the evolution of such entities is described by means of a graph structure and finally it groups together spatio-temporal entities that evolve similarly. The analysis were performed on three study areas to highlight inter (among the study areas) and intra (inside a study area) similarity by following the evolution of the underlying phenomena. The analysis demonstrate the benefits of our methodology. Moreover, we also stress how an expert can exploit the extracted knowledge to pinpoint relevant landscape evolutions in the multi-annual time series and how to make connections among different study areas.     

数字滤波器的频谱窗和噪声压缩度

根据傅里叶理论导出了数字滤波器的频谱窗，根据随机过程理论导出了数字滤波的噪声压缩度。通过对二项式系数数字滤波器和多项式系数数字滤波器和频谱窗和噪声压缩度的分析，发现前者对噪声具有较强的压缩作用，同时能保持信号的凹凸性，是一种优于后者的数字滤波器。