Performance Evaluation of a Self-Developed Ozonesonde and Its Application in an Intensive Observational Campaign

To make a detailed test on the reliability and detection performance of the electrochemical concentra- tion cell （ECC） type ozonesonde which had been devel- oped and preliminarily evaluated by the authors, an inten- sive ozonesonde release experiment was held at two sites in Beijing and Changchun in June 2013. The results showed that the mean background current and its standard deviation were 0.03 （0.04） pA and 0.02 （0.03） pA in Bei- jing （Changchun）. The average response time and its standard deviation were 27.8 s （30.4 s） and 4.0 s （3.7 s） in Beijing （Changchun）. The ozone partial pressure profiles at both sites showed a central peak in the stratosphere and a side peak in the boundary layer. Large variation in ozone partial pressure was observed at the middle levels of the atmosphere （10-17 kin）. A more marked gradient of ozone change was observed in Beijing （3.4 mPa km-1） at the lower atmosphere level, as compared to that in Changchun （0.4 mPa km-l）. The results presented in this paper indicate that this self-developed ozonesonde shows a high level of reliability and good performance. The ozonsonde is expected to play an important role in opera- tional observations of ozone profiles.     

基于阈值区间的海洋锋面提取模型

A model （Bayesian oceanic front detection, BOFD） of sea surface temperature （SST） front detection in satel- lite-derived SST images based on a threshold interval is presented, to be used in different applications such as climatic and environmental studies or fisheries. The model first computes the SST gradient by using a Sobel algorithm template. On the basis of the gradient value, the threshold interval is determined by a gradi- ent cumulative histogram. According to this threshold interval, front candidates can be acquired and prior probability and likelihood can be calculated. Whether or not the candidates are front points can be deter- mined by using the Bayesian decision theory. The model is evaluated on the Advanced Very High-Resolution Radiometer images of part of the Kuroshio front region. Results are compared with those obtained by using several SST front detection methods proposed in the literature. This comparison shows that the BOFD not only suppresses noise and small-scale fronts, but also retains continuous fronts.     

2012年秋季白脊管藤壶在江苏如东互花米草盐沼向附着及分布

互花米草Spartina alterniflora自1979年引入至今,已在我国海岸带大范围扩张并对盐沼湿地生态系统产生了很大影响.本研究以附着生物藤壶为例,研究了互花米草扩张对附着生物的影响.通过对5个断面共28个样方的米草植株、附着藤壶以及藤壶在互花米草上的最大附着高度调查,获得结果如下:藤壶在互花米草滩上的附着范围位于潮沟两侧,且呈宽度约为5 m的带状分布;潮沟规模越大,其向陆方向的延伸范围越宽;每个站位藤壶附着的相对最大高度都位于同一水平.附着藤壶均为白脊管藤壶Fistulobalanus albicostatus,平均干重237±69g·m-2,大部分藤壶直径在2～10mm之间.互花米草的平均干重为981±81g·m-2,潮沟附近互花米草高壮但密度较小,远离潮沟互花米草矮小但密度较大.分析表明,互花米草为藤壶提供了附着基质,并影响藤壶在潮间带的平面分布格局(尽管藤壶的生态位保持不变).影响白脊管藤壶分布特征的原因主要是海水浸没时间的差异;负地形的浸没时间更有利于藤壶的附着和生存;另外潮沟较高的潮水流速除了利于白脊管藤壶幼体的附着外,还可以通过水流的涨、落为其带来充足的食物.     

一种改进的无人机航摄影像快速拼接方法

为提高无人机航摄影像快速拼接的速度和精度,针对无人机影像处理特点,提出重叠区分块并行处理策略;通过对不同图像分辨率和尺度下的特征匹配情况进行分析,提出分块阈值自适应调节方法来改进尺度不变特征转换(SIFT)算法;利用匹配点距离中误差进行粗差去除,获取最优随机一致性检验(RANSAC)样本,得到更精确匹配点对。试验结果证明,改进策略既可保证拼接精度,又可提高拼接效率。     

利用ASTER-GDEM提取川中丘陵区水系

本文以ASTER GDEM为基本数据源,基于均值变点方法,选取合适的汇流阈值,得到川中丘陵区嘉陵江支流西河流域水系;在此基础上对其沟谷段特征进行了研究。结果表明,均值变点方法能较好判定提取川中丘陵区西河水系的汇流阈值;ASTER-GDEM总体上能较好描述丘陵地区沟谷水系;西河水系源头区沟谷段偏长,侵蚀较为强烈。     

Applications of wavelet analysis in differential propagation phase shift data de-noising

Using numerical simulation data of the forward differential propagation shift （ΦDP） of polarimetric radar,the principle and performing steps of noise reduction by wavelet analysis are introduced in detail.Profiting from the multiscale analysis,various types of noises can be identified according to their characteristics in different scales,and suppressed in different resolutions by a penalty threshold strategy through which a fixed threshold value is applied,a default threshold strategy through which the threshold value is determined by the noise intensity,or a ΦDP penalty threshold strategy through which a special value is designed for ΦDP de-noising.Then,a hard-or soft-threshold function,depending on the de-noising purpose,is selected to reconstruct the signal.Combining the three noise suppression strategies and the two signal reconstruction functions,and without loss of generality,two schemes are presented to verify the de-noising effect by dbN wavelets：（1） the penalty threshold strategy with the soft threshold function scheme （PSS）; （2） the ΦDP penalty threshold strategy with the soft threshold function scheme （PPSS）.Furthermore,the wavelet de-noising is compared with the mean,median,Kalman,and finite impulse response （FIR） methods with simulation data and two actual cases.The results suggest that both of the two schemes perform well,especially when ΦDP data are simultaneously polluted by various scales and types of noises.A slight difference is that the PSS method can retain more detail,and the PPSS can smooth the signal more successfully.     

基于点的多尺度形态学重建滤波方法EI北大核心CSCD

针对现有机载激光雷达(LiDAR)点云滤波算法难以准确分离复杂地形中地面点与地物点问题,提出了一种基于点的多尺度形态学重建滤波方法 PMMF (Point-based Multi-scale Morphological reconstruction Filter)。在初始尺度层次下,PMMF通过构建一种基于点的形态学重建对原始点云滤波,即先在掩膜点云约束下借助k邻域结构元素和高程缓冲区反复膨胀标记点云,获取潜在地面点;然后通过自适应坡度方法剔除潜在地面点中的非地面点,其中,坡度阈值随地形复杂度自适应变化。在上层滤波结果基础上,PMMF通过提升种子点选择的网格尺度重复上层滤波过程,直至结果收敛。以国际摄影测量与遥感学会(ISPRS)发布的15组基准数据为研究对象,将PMMF滤波结果与近5年(2016年—2020年)提出的15种滤波算法比较表明,PMMF有8组数据滤波效果占优,15组数据平均总误差和Kappa系数分别为2.71%和91.08%。使用4种不同地形特征的高密度机载LiDAR点云数据进一步验证PMMF的滤波效果,并将计算结果与简单形态学滤波(SMRF)、布料模拟滤波(CSF)、渐进加密三角网滤波(PTD)和多分辨率层次滤波(MHF)比较。结果表明,PMMF滤波性能最优,平均总误差为3.24%,较其他4种滤波方法分别减小了12.0%、59.1%、70.1%和53.2%。     

小波阈值去噪方法在重力资料处理中的应用

简要介绍了小波变换的基本理论与小波阈值去噪实现过程。通过单球体与双球体模型试验,探讨了阈值去噪时小波基以及分解层数的选择问题;最后利用小波阈值去噪方法,对某实测布格重力资料进行处理,有效滤除了随机噪声。去噪后计算的水平方向导数明显比去噪前直接计算的水平方向导数效果好。     

基于遥感影像的黄河内蒙古段冰-水分类研究

及时获取凌汛期河冰和水体的空间分布特征,对于预测冰凌灾害、提高防凌信息化管理水平有重要意义。遥感技术是当前获取河冰和水体空间分布的最主要手段之一。但是,黄河水体有大量悬浮泥沙,这给基于遥感技术的高精度冰-水分类带来了挑战。以黄河内蒙古段为例,基于Landsat 8 OLI遥感影像数据,在利用归一化积雪指数（NDSI）及河道矢量数据排除无关地物的基础上,对比了近红外波段反射率值、归一化差异水体指数（NDWI）、归一化积雪指数（NDSI）、改进的归一化积雪指数（MNDSI）以及归一化差异未封冻水体指数（NDUWI）在黄河内蒙古段典型河道河冰、水体分类中的表现,计算各指标总体分类精度及Kappa系数并进行阈值稳定性分析。结果表明：在利用NDSI和高清历史影像排除河道外无关地物后,NDUWI在各子段影像中的总体分类精度和Kappa系数均达到90.00%及0.90以上,其河冰、水体最优区分阈值大体分布于阈值中值附近。研究结果可为凌汛期黄河冰凌监测方法的选取以及冰上爆破位置的拟定提供依据。