Co-registration and correlation of aerial photographs for ground deformation measurements

We describe and test a procedure to accurately co-register and correlate multi-temporal aerial images. We show that this procedure can be used to measure surface deformation, and explore the performance and limitations of the technique. The algorithms were implemented in a software package, COSI-Corr (available from the Caltech Tectonics Observatory website). The technique is validated on several case examples of co-seismic deformation. First, we measure co-seismic ground deformation due to the 1992, Mw 7.3, Landers, California, earthquake from 1 m resolution aerial photography of the National Aerial Photography Program (United States Geological Survey). The fault ruptures are clearly detected, including small kilometric segments with fault slip as small as a few tens of centimeters. We also obtained similar performance from images of the fault ruptures produced by the 1999 Mw 7.1 Hector Mine, California, earthquake. The measurements are shown to be biased due to the inaccuracy of the Digital Elevation Model, film distortions, scanning artifacts, and ignorance of ground displacements at the location of the tie points used to co-register the multi-temporal images. We show that some of these artifacts can be identified and corrected.     

Methods of adjusting space systems data and terrestrial measurements

Various space systems use coordinate systems differing among each other as to coordinate origin, orientation, and scale, which brings about systematic differences between results obtained by the different techniques. A reconciliation of these differences can be achieved in a combined adjustment in which certain groups of observations are assigned transformation parameters as unknowns. This method is extended to combined adjustments of three-dimensional and terrestrial data in areas of continental extent.     

基于NDVI先验知识的LAI地面采样方法

针对非均质中低分辨率像元的叶面积指数LAI验证中如何布设基本采样单元ESU的问题,提出基于NDVI先验知识的ESU布设方法,并采用不同植被类型、不同均匀程度的地表作为模拟场,分析对比了方法的精度及稳定性。结果显示,本文方法用NDVI先验知识描述植被的生长空间分布信息,能相对准确地划分植被的不同生长水平,有效降低层内方差。在草地和森林地区的试验中,精度与稳定性均优于传统的随机采样、均匀采样和基于分类图的3种采样方法。因此,本文提出的采样方法为大尺度非均质区域LAI地面验证的采样方案提供了新的设计思路。     

DETERMINATION OF WEIGHTED MEAN TROPOSPHERIC TEMPERATURE USING GROUND METEOROLOGICAL MEASUREMENTS

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Determination of weighted mean tropospheric temperature using ground meteorological measurements

The weighted mean tropospheric temperature is a critical parameter in the conversion of wet zenith delay to precipitable water vapor in GPS Meteorology. This parameter can not be calculated from the radiosonde data in real time through the conventional methods. In this study, we first discuss the admissible error of weighted mean temperature to enable the accuracy of the conversion better than 1 mm, then summarize the performance of some of the existing methods. An empirical formula is established that satisfies the real-time requirement in GPS meteorology using Sequential Regression Analysis method. It is shown that this real-time formula as compared with other empirical methods is more accurate for local applications.     

利用Landsat TM数据和地面观测数据验证GLASS反照率产品

Global LAnd Surface Satellite Products System(GLASS)反照率产品基于Angular Bin(AB)算法,仅使用单一观测角度的地表或大气层顶反射率数据就能较为准确地反演地表宽波段反照率,具有较高的时间分辨率,可以反映降雪、融雪、收割等状况下地表反照率的快速变化。遵循"一检两恰"的验证流程对这一反照率产品进行验证,首先使用FLUXNET站点验证数据对AB算法反演的Landsat Thematic Mapper(TM)高分辨地表反照率数据进行验证,再将TM高分辨反照率聚合到GLASS像元尺度对GLASS反照率产品进行验证。挑选FLUXNET的5个站点,筛选无云条件下的TM高分辨率影像,共获得103组有效验证数据。验证结果表明,GLASS反照率产品具有较高的精度,总体误差约为0.0163,可以满足大多数应用的精度需求。     

深空探测巡视器视觉导航定位方法研究与地面试验场验证

地外天体表面巡视器就位探测是深空探测研究的重要手段,其自主导航定位能力是任务开展的重要前提。本文主要对视觉导航方法中的视觉同时定位与地图构建(SLAM)方案开展应用研究。介绍了当下经典的视觉SLAM框架,并以具有代表性的ORB-SLAM3算法为例开展研究;分别利用公开数据集、深空探测地面模拟场数据进行试验验证,探索视觉导航定位算法在深空探测场景下的有效性。本文研究为我国后续开展长距离连续巡视任务提供参考。     

基于角锥体原理的空间后方交会改进算法

在摄影测量中,空间后方交会是一个很重要的概念,通过空间后方交会可以确定像片的外方位元素,从而确定像片在物方空间坐标系中的位置和姿态。本文在文献[1][2]的基础上,对其中部分复杂公式进行改进,得到了表达形式简单,且易于理解和解算的实用公式,并通过实例证明改进算法的正确性。     

一种改进的InSAR城市地面沉降监测精度评价方法

针对InSAR沉降监测精度评定方法的单一性,综合考虑建筑物自身沉降和时空基准难以统一的问题,构建了改进的反距离权重插值模型。以宁波东部新城某沉降区域的PS-InSAR监测结果为试验数据,在统一时空基准的前提下,利用改进IDW插值模型对监测结果进行精度评定,并以交叉验证的方式验证了该插值方法的准确性。试验证明：通过对比两个实测水准点,使用改进的IDW插值获取的InSAR监测结果误差为0.3和0.8,相比于普通IDW和Kriging方法提高了大约1.1 mm。     

GPS measurements of ocean loading and its impact on zenith tropospheric delay estimates: a case study in Brittany, France

 The results from a global positioning system (GPS) experiment carried out in Brittany, France, in October 1999, aimed at measuring crustal displacements caused by ocean loading and quantifying their effects on GPS-derived tropospheric delay estimates, are presented. The loading effect in the vertical and horizontal position time series is identified, however with significant disagreement in amplitude compared to ocean loading model predictions. It is shown that these amplitude misfits result from spatial tropospheric heterogeneities not accounted for in the data processing. The effect of ocean loading on GPS-derived zenith total delay (ZTD) estimates is investigated and a scaling factor of 4.4 between ZTD and station height for a 10° elevation cut-off angle is found (i.e. a 4.4-cm station height error would map into a 1-cm ZTD error). Consequently, unmodeled ocean loading effects map into significant errors in ZTD estimates and ocean loading modeling must be properly implemented when estimating ZTD parameters from GPS data for meteorological applications. Ocean loading effects must be known with an accuracy of better than 3 cm in order to meet the accuracy requirements of meteorological and climatological applications of GPS-derived precipitable water vapor. Received: 16 July 2001 / Accepted: 25 April 2002 Acknowledgments. The authors are grateful to H.G. Scherneck for fruitful discussions and for his help with the ocean loading calculations. They thank H. Vedel for making the HIRLAM data available; D. Jerett for helpful discussions; and the city of Rostrenen, the Laboratoire d'Océanographie of Concarneau, and the Institut de Protection et de S?reté Nucléaire (BERSSIN) for their support during the GPS measurement campaign. Reviews by C.K. Shum and two anonymous referees significantly improved this paper. This work was carried out in the framework of the MAGIC project (http://www.acri.fr/magic), funded by the European Commission, Environment and Climate Program (EC Contract ENV4-CT98–0745). Correspondence to: E. Calais, Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN 47907-1397, USA. e-mail: ecalais@purdue.edu Tel. : +1-765-496-2915; Fax:+1-765-496-1210     

Effect of raindrop size distribution variability in dual-frequency radar rain retrieval algorithms assessed from disdrometer measurements

The effect of natural variation of raindrop size distribution (DSD)on the retrieval of rainfall rate from the dual-frequency (13.6/35.5 GHz,as will be in the Global Precipitation Measurement Mission) Precipitation Radar (DPR) measurements is studied by utilizing a large set of disdrometer-measured DSD data through a simple simulation framework. A DPR inversion technique(DPR-IT) that focuses on the retrieval of DSD information from the non-Rayleigh backscattering characteristic of the hydrometeors and a conventional DPR technique(DPR-CT) that focuses on the independent retrieval of rainfall rate from the attenuation measurement are considered in this analysis. The preliminary results show that at different rainfall rate regions these methods have different responses to the DSD variability. For instance, it appears that DPR-IT suffers relatively less from the DSD variability in the regions of weak to moderate rainfall rate (/spl bsol/ mm /spl middot/ h/sup -1/),while in the strong rainfall rate (>/spl sim/10 mm /spl middot/ h/sup -1/) region the DPR-CT generally has less sensitivity to DSD variations than the DPR-IT.     

利用高分影像和珞珈一号数据进行住房空置率高精度空间估算

本文主要利用珞珈一号夜间灯光数据和高分遥感影像数据,提出了一种对研究区按建成区高层区、建成区低层区和非建成区住房进行空置率分区块估算的方法,采用夜晚实地记录的方法对估算结果进行精度检验,并通过LISA聚集图分析其空间聚集情况.表明结果:①研究区整体住房空置率为17.88％,均方根误差为0.14,其中非建成区的住房空置率...     

一种浅水摄影测量水下相机的防护装置

本文为摄影机和目标物均在水中的水下摄影测量设计了一种适用于浅水的水下摄影测量相机防护装置,并详细介绍了该装置的结构组成、安装和卸载步骤以及该装置的特点和使用注意事项,最后用本文研制的相机水下防护装置对一小天线进行水下试验,实验结果与空气中测量的结果高度一致.     

Experimentation of structured light and stereo vision for underwater 3D reconstruction

Current research on underwater 3D imaging methods is mainly addressing long range applications like seafloor mapping or surveys of archeological sites and shipwrecks. Recently, there is an increasing need for more accessible and precise close-range 3D acquisition technologies in some application fields like, for example, monitoring the growth of coral reefs or reconstructing underwater archaeological pieces that in most cases cannot be recovered from the seabed. This paper presents the first results of a research project that aims to investigate the possibility of using active optical techniques for the whole-field 3D reconstructions in an underwater environment. In this work we have tested an optical technique, frequently used for in air acquisition, based on the projection of structured lighting patterns acquired by a stereo vision system. We describe the experimental setup used for the underwater tests, which were conducted in a water tank with different turbidity conditions. The tests have evidenced that the quality of 3D reconstruction is acceptable even with high turbidity values, despite the heavy presence of scattering and absorption effects.     

极化信息在水下地形SAR探测中的应用

现有的水下地形SAR(Synthetic Aperture Radar)探测模型尚未综合应用SAR的极化信息。本文基于Valenzuela的雷达散射截面表达式与袁业立提出的海波高频谱表达式,并结合全极化SAR相干斑抑制的极化白化滤波法,将极化信息有效地运用到水下地形SAR探测中去。最后,以中国台湾浅滩为例,分别利用Radarsat-2单一极化和全极化影像开展水下地形SAR探测研究,探测结果表明充分利用全极化信息的探测精度明显优于单一极化信息的探测精度,利用极化信息可以有效地提高水下地形SAR探测精度。     

水下导航定位技术综述

自主式水下航行器(AUV)作为海洋资源的开发与利用的主要载体,执行任务时需要准确的定位信息. 现有AUV主要采用捷联惯性导航系统(SINS)为主,声学导航和地球物理场匹配导航技术为辅的导航方式. 本文简述水下导航方式基本原理、优缺点和适用场景;探讨各类导航方式包含的关键技术,提高组合导航精度和稳定性. 通过分析现阶段存在问题,展望水下导航的未来发展趋势.      

Atmospheric correction to IRS-P6 AWiFS data and its validation with ground measurements: A study over the semi-arid region

In this study, we have implemented a fast atmospheric correction algorithm to IRS-P6 advanced wide field sensor (AWiFS) satellite data for retrieving surface reflectance under different atmospheric and surface conditions. The algorithm is based on MODIS climatology products and simplified use of Second Simulation of Satellite Signal in Solar Spectrum (6S) radiative transfer code. The algorithm requires information on aerosol optical depth (AOD) for correcting the satellite dataset. The atmospheric correction algorithm has been tested for IRS-P6 AWiFS False colour composites covering the International Crops Research Institute for the Semi-Arid Tropics Farm, Patancheru, Hyderabad, India, under varying atmospheric conditions. Ground measurements of surface reflectance representing different land use/land cover, i.e. red soil, chick pea, groundnut and pigeon pea crops were conducted to validate the algorithm. Terra MODIS AOD₅₅₀ validated with Microtops-II sun photometer–derived AOD₅₀₀ over the urban region of Hyderabad exhibited very good correlation of ～0.92, suggesting possible use of satellite-derived AOD for atmospheric correction.