一种遥感影像同名点密集匹配方法

针对在遥感相机检校、三维重建、信息提取、变化监测等应用中,都需要在影像中每隔若干个点、甚至是逐点寻找密集同名点的情况,该文将基于特征的方法和基于模板的方法相结合,提出一种新的高精度的密集同名点提取方法。将参考影像降采样为与遥感影像同一分辨率,然后使用SIFT算法提取粗精度同名点,建立全局几何模型,使用其将遥感影像每个像元及其邻域投影到参考影像,并以其为模板,应用优化相位匹配法获取高精度同名点。经实验验证,只要遥感影像和参考影像中相应区域的景物变化不大,该文方法可以有效地确定密集的高精度同名点对。     

A Spectral-Mixing Model for Estimating Sub-Pixel Coverage of Sea-Surface Floating Macroalgae

ABSTRACT

In the past decade, floating macroalgae blooms have been increasing on a global scale. Sub-pixel coverage of floating macroalgae in a remote-sensing image is a crucial parameter for the estimation of biomass. In this study, in situ spectra of green macroalgae (Ulva prolifera), brown macroalgae (Sargassum horneri), and sea water were collected, and they were used to simulate the spectra of macroalgae–seawater mixtures in a linear mixing way. Three algae indices, normalized difference of vegetation index (NDVI), difference of vegetation index (DVI), and virtual-baseline reflectance height for floating algae (VB-FAH) derived from the spectra, were examined with the coverage of macroalgae. The results show that all three indices increase monotonically with increasing sub-pixel coverage of macroalgae: VB-FAH and DVI increase linearly, while NDVI shows a logarithmic increase. Based on this characteristic, two sub-pixel coverage models were proposed (i.e., a linear model based on VB-FAH (or DVI) and an exponential model based on NDVI). These models were then applied to the multiple-spectral GaoFen-1 (GF-1, 16?m resolution) satellite image to examine the sub-pixel coverage of green tide in the Yellow Sea caused by the bloom of floating green macroalgae (U. prolifera). The results show that the relative differences between the two models are no more than 5%, indicating good consistency between the two models. Taking into account the sensitivity of these models (or indices) to the coverage of macroalgae, as well as atmospheric and sea surface conditions and their simplicity, we suggest using the linear model based on VB-FAH, DVI, or a similar band-difference index to estimate sub-pixel coverage of floating macroalgae.     

A Waveform Similarity Approach to Investigate Seismicity Patterns

the temporal and spatial evolution of seismicity, a simple cross-correlation technique was applied to a waveform data set of western Alps earthquakes. A selection of events recorded by a reference station of the regional seismic network of North-Western Italy (IGG network) within a particular S-P range was used. The adopted method was tested on 380 events recorded in 1995, allowing for the definition of the critical parameters for an optimal identification of earthquake families.The comparison of the individuated families definition with the relevant epicentres map confirms that, on small scales, the epicentre positions of microearthquakes located by a regional network could be strongly influenced by location errors. The analysis was extended to a more complete data set of 2653 events; 1171 of them were grouped in families. The results demonstrated that our single station method is able to discriminate between closely spaced families on the basis of the position and of the radiation properties.     

一种改进后的交叉相关法(COTREC)在降水临近预报中的应用

利用多普勒雷达资料,采用一种改进后的交叉相关法(COTREC)建立了一种降水临近预报方法。COTREC法的基本原理是对传统交叉相关法(TREC)反演的风场进行水平无辐散处理,得到COTREC风场,用新的风场外推得出的回波能够保持平滑连续的形状。但是这种方法也存在缺陷,由于采用水平无辐散限制,使得外推反演得到的风场在不同程度上受到削弱,从而外推后的回波略慢于实况观测的回波。通过引入数值预报平均风场作为TREC风场背景场,较好地解决了TREC风场受到削弱的问题,并用该方法对2007年6月23—24日强雷雨天气和2007年台风“圣帕”两次降水过程进行了预报试验,试验结果表明：采用改进后的交叉相关方法的降水临近预报与雷达实际观测比较一致,可作为台风、强对流等灾害性天气的降水临近预报方法之一。     

互相关-小波分析在钻探地层识别中的应用

钻探工程中实时掌握钻头钻进过程且能实时诊断地层是提高钻探效率的关键因素之一。基于钻头在不同介质层激发的振动信号特点,提出互相关-小波变换分析法,将互相关用于提取预判层或目标层的时延信息,并利用小波变换对互相关域进行多分辨率分析,提取凸显成分时频特征,据此快速识别地层。仿真分析和试验均表明：互相关-小波变换分析能准确地表征时延信息和时频特征,能实时地预测钻头钻进情况并获取地层信息,具有很强的实时性和准确率,在提高现场钻探效率中有一定的实用价值。     

三种算法联合迭代反演求取最佳剩余静校正量

估算剩余静校正量可看作是以激发点及接收点剩余静校正量为模型参数的、以叠加能量为目标函数的全局最优值的搜索问题．当地震记录的剩余静校正量大而信噪比较低时，应用相关统计法不能有效地拾取静校正量．本文分别采用了ＣＭＰ道集内道间互相关法、图像边缘提取的Ｌａｐｌａｃｉａｎ算法及ＤＦＰ算法，三种不同算法联合迭代反演可求取最佳的模型参数，使目标函数值达到或接近于全局最优．理论试算及实际资料处理效果表明，这种方法能够解决低信噪比及大静校正量造成的周期跳跃等静校正问题．     

Spatial simulation of geologic variables

Analytical formulation of a general simulation model for generation of anisotropic as well as isotropic synthetic patterns in one, two, or three dimensions is proposed. It has significance for the purpose of modeling geologic properties such as ore grades, reservoir porosity, mineral distribution, fracture spacings, aperture, orientations, etc. General procedures for such a simulation by the autoregressive process are given for model parameters estimation and synthetic pattern generation. The model works on the square net basis and generates sequential patterns first along any desired direction for unidimensional simulation and then two-dimensional patterns are constructed with reference to two orthogonal unidimensional sequences. Applications to synthetic two-dimensional pattern are shown for isotropic cases with different model parameters. The extension of the model to three-dimensional space is readily available.     

Observation of the seismoelectric effect in a gas condensate field in the Earth’s natural electromagnetic and seismic noise of 0.1-20 Hz

The first experimental measurements of the cross-correlation function (CCF) of the Earth’s seismic and electrical noise were carried out in two areas of the Minusinskoe gas condensate field in 2014 and 2015 using a VPEMPZ-M1 (Shum-6) two-channel geophysical device developed at Siberian Federal University. The Earth’s seismic noise and electrical noise in the frequency range 0.1-20 Hz were received by a geophone and an electric dipole, respectively. In both cases, a productive pool at depths of 1800-2000 m had a maximum CCF value five to seven times higher than the normal background, indicating the occurrence of the seismoelectric effect in passive fields.     

青藏高原东北缘祁连山地区地震台阵背景地噪声特征

基于祁连山地区78个地震台站的垂直分量连续波形记录,计算台站对之间背景噪声的互相关函数,并叠加得到5—10 s和10—20 s两个周期的瑞利面波信号。利用归一化振幅方法,分析不同周期范围的噪声源能量在不同方位随季节变化的规律。研究结果显示:祁连山地区5—10 s周期背景噪声的能量优势来源,夏季集中在110°—170°方位,冬季集中在300°—350°方位,但在110°—150°方位也有相对微弱的能量分布,表明第二微震带的噪声能量来源在夏季主要来源于太平洋的海洋活动,冬季主要来源于大西洋的海洋活动;10—20 s周期背景噪声的能量优势来源在夏季集中在70°—150°和170°—230°方位,在冬季则集中在290°—350°和70°—130°方位,表明第一微震带的噪声能量在夏季主要来源于印度洋的海洋区域,冬季主要来源于北大西洋和太平洋。由于2个周期的背景噪声源在祁连山地区存在明显的季节差异,因此在利用背景噪声方法研究该地区介质速度结构时,需充分考虑噪声源非均匀性产生的影响。     

Evaluation of diverse classification approaches for land use/cover mapping in a Mediterranean region utilizing Hyperion data

Information on Earth's land surface cover is commonly obtained through digital image analysis of data acquired from remote sensing sensors. In this study, we evaluated the use of diverse classification techniques in discriminating land use/cover types in a typical Mediterranean setting using Hyperion imagery. For this purpose, the spectral angle mapper (SAM), the object-based and the non-linear spectral unmixing based on artificial neural networks (ANNs) techniques were applied. A further objective had been to investigate the effect of two approaches for training sites selection in the SAM classification, namely of the pixel purity index (PPI) and of the direct selection of training points from the Hyperion imagery assisted by a QuickBird imagery and field-based training sites. Object-based classification outperformed the other techniques with an overall accuracy of 83%. Sub-pixel classification based on the ANN showed an overall accuracy of 52%, very close to that of SAM (48%). SAM applied using the training sites selected directly from the Hyperion imagery supported by the QuickBird image and the field visits returned an increase accuracy by 16%. Yet, all techniques appeared to suffer from the relatively low spatial resolution of the Hyperion imagery, which affected the spectral separation among the land use/cover classes.