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MODIS数据预处理方法


2013 年 6 月 第 11 卷第 3 期
doi:10.11709/j.issn.1672-4623.2013.03. 018

地理空间信息
GEOSPATIAL INFORMATION

Jun.,2013 Vol.11,No.3

MODIS 数据预处理方法
张 怡 1,2,何政伟 1,2,薛东剑 2
(1. 地质灾害防治与地质环境保护国家重点实验室,四川 成都 610059 ; 2. 成都理工大学 地球科学学院,四川 成都 610059) 摘 时间、大气、太阳辐射的改变,导致获取的相邻遥感影像的对比度及光亮度产生差异,为了更好地进行分析、评价, 要:

需对遥感数据进行预处理。以新疆天山公路及其周边为研究区域,基于 MODIS 数据,利用 ENVI 软件进行数据的预处理,包 括数据的几何校正、图像拼接、图像裁剪等,为其后进行的积雪研究作数据准备。 MODIS ; ENVI ; 预处理 关键词 : P237.3 中图分类号 : B 文献标志码 : 1672-4623(2013)03-0049-02 文章编号 :

遥感数据的预处理主要包括对遥感图像进行辐射 校正和几何纠正、 图像整饰、 投影变换、 镶嵌、 特征提取、 分类以及各种专题处理的方法。MODIS 数据拥有覆盖 面积和涉及波段广、 免费获取、 数据更新频率高等优点, 已广泛应用于科学研究、农业生产评估、地质灾害预 警等领域。本文对天山公路附近区域的 MODIS 数据进 行了预处理,为之后的雪深反演、积雪面积计算、雪 害评价研究等作好数据准备。

功能,能够进行二次开发,加入其他所需的功能 ; 与 ESRI 公司的全面合作,能与 ArcGIS 完美地整合,为遥 感和 GIS 的一体化集成提供了一个最佳的解决方案。

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2.1

MODIS 数据预处理
图像的几何校正 几何校正是指对由于 MODIS 探测器对地球观测的

视野几何特性、地球表面的曲率、地形起伏和探测器运 动中的抖动等因素的共同影响产生的影像几何畸变进行 校正的过程 [5]。由于上述因素的共同影响,MODIS 1B 数据存在几何畸变,特别是 MODIS 1B 数据的扫描条 带之间的错位现象十分严重, 俗称“双眼皮” 。 “双眼皮” 现象随着观测角度的增大而变得严重。计算表明,在视 角为 24°时,条带之间的重叠度为 10%,而在条带的 两端重叠度达到 50%[6,7]。因此针对 MODIS 数据除了要 进行几何校正外,还需去除其“双眼皮”现象,也叫 Bow-tie 处理。而在 ENVI 中既有专门的 MODIS 数据 几何校正功能模块 Georeference MODIS,也有去除“双 眼皮”现象的 Perform Bow Tie Correction 模块。 ENVI 根据 MODIS 数据本身的坐标经纬度信息进 行地理坐标定位。利用每行数据有的 51 个经纬度值, 进行地理坐标定位从而对图像校正。在我们选择了所 需的图像波段后,会弹出 MODIS 数据几何校正界面, 在进行几何校正前,需要输入图像的投影信息。由于 我们选择的是 UTM 坐标系统,在标有“Zone”的文 本框里,输入区域号,或点击“Set Zone”按钮,键入 经纬度值,自动计算出区域号。 图 1 是几何校正前图像的局部图,能够看出明显 的“双眼皮”现象,其错位的条带严重影响了图像的

1 MODIS 数据及软件介绍
美国地球观测卫星 (EOS) 系列中的第一颗上午太 阳同步 Terra 卫星携带的中分辨率成像光谱仪 MODIS 是 EOS 卫星系列中最主要和最有特色的仪器。MODIS 具有较高的光谱分辨率,为 36 个波段,地面分辨率分 别为 250 m (1 ~ 2 波段 ),500 m(3 ~ 7 波段 ),1 000 m(8 ~ 36 波段 ),扫描观测宽度达 2 330 km,影像数 据可以每天上、下午获取,并免费接收
[1-3]

。MODIS

拥有的这 36 个光谱波段的地球综合信息对于开展自然 灾害与生态环境监测、全球环境和气候变化研究以及 进行全球变化的综合性研究等具有重要意义。为了有 效地提取雪的覆盖面积和反演雪深深度,本文采用的 主要是 500 m 分辨率的二级数据产品 MODIS 1B 数据。 MODIS 数据根据处理程度划分成多级,MODIS 1B 数 据属于二级产品,即在原始数据上进行了定标定位后 产生的数据,可被软件直接读取和处理。 本文采用的是 ENVI 软件,是美国 ITT VIS 公司的 旗舰产品,它是快速、便捷、准确地从影像中提取信息 的首屈一指的软件工具 。 其具有强大的图像处理功能; 专业的高光谱分析功能 ; 独有的 IDL 支持强大的扩展
[4]

2012-11-08。 收稿日期 : 国家自然科学基金资助项目(40972225) ; 教育部博士点基金联合资助项目(20095122110003) 。 项目来源 :

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地理空间信息

第 11 卷第 3 期

视觉效果,也对之后进行的各种积雪分析造成影响。 图 2 为几何校正后的局部图。图 3 和图 4 是整幅图像 几何校正前后的对比,校正后的图像有较大的拉伸及 变形,消除了图像的几何畸变,更好地还原了图像, 真实地反映了图像所表示的各项地理信息。从图 4 可 看出, 条带错位现象已经被消除, 图像有被拉伸的情况。

矢量面文件进行投影变换,将研究区矢量面 shape 文件 的 Krasovsky_1940_Transverse_Mercator 坐标系统转换成 WGS84 的地理坐标系 ; 在 ENVI 中将矢量面文件转换成 ROI,然后通过 Subset data via ROI 完成对 MODIS 影像 的裁剪。如图 6 所示,裁剪后的图像由 143 波段合成真 彩色,可清晰地看到白色的积雪、山脉、云等。

图 5 研究区积雪所需行列显示 图 1 几何校正前局部图 图 2 几何校正后局部图

图 3 几何校正前整幅图

图 4 几何校正后整幅图

图 6 裁剪后图像

2.2

图像的拼接 图像拼接又被称为图像镶嵌,是将相邻几幅遥感

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图像合成 1 幅图。由于本文的研究区南北狭长,经纬跨 度为 80°E~85°E、40°N~45°N,覆盖该区域有 h24v04、 h23v04 2 个 数 据 块, 需 要 进 行 拼 接 处 理。ENVI 的 Mosaicking 工具能根据图像所带的地理坐标进行自动 拼接,拼接前需要进行直方图调节,使拼接后的效果 良 好。 除 了 常 见 的 遥 感 处 理 软 件 ENVI,ERDAS 能 对 MODIS 数据进行拼接处理,还有一种能专门针对 MODIS 数据进行基本处理的软件 MRT,即 MODIS Reprojection Tool,能自动拼接 MODIS 数据,输出多 种 格 式 数 据, 如 raw-binary、GeoTiff 和 HDF-EOS, 图 5 为本文研究的两景 MODIS 数据所在。 2.3 图像的裁剪 一幅 MODIS 数据的扫描范围为 1 275 km×2 330 km, 而本文中所需的研究区为天山公路附近区域,因此需要 对拼接好的图像进行裁剪。在 ENVI 中提供了多种裁剪 方式 : ①直接输入行列数进行裁剪 ; ② Image 裁剪,直 接在图像上框选区域进行裁剪 ; ③ Map 裁剪,直接输 入经纬度,以左上点、右下点坐标为基准进行裁剪 ; ④ Flie 裁剪,用其他的图像对其进行裁剪 ;⑤ ROI/ EVF 裁剪,即感兴趣区裁剪,先在 ArcGIS 下将研究的

由于 MODIS 数据分辨率高、覆盖范围广、免费等 优点,已经被广泛应用于各行各业。本文根据需要对 MODIS 数据进行了几何校正,拼接和裁剪等预处理, 为之后计算积雪覆盖面积,反演积雪深度,建立空间 数据库等提供了良好的基础数据。

参考文献
[1] [2] [3] [4] [5] [6] [7] 赵英时 , 章申 , 秦大河 , 等 . 遥感应用分析原理与方法 [M] . 北京 : 科学出版社 ,2004 总装备部卫星有效载荷及应用技术专业组应用技术分组 . 卫 星应用现状与发展 [M] . 北京 : 中国科学技术出版社 , 2001 杜启胜,刘志平,王新生,等 . 基于 ENVI 的 MODIS 数据 预处理方法 [J]. 地理空间信息,2009,7(4) : 98-100 武艺,文先华 . 利用 ENVI 软件处理遥感影像 [J]. 科技信息, 2011,2(16) : 376-377 袁金国 . 遥感图像数字处理 [M]. 北京: 中国环境科学出版社, 2006 马建文,韩秀珍 . 东亚飞蝗灾害遥感监测机理与方法 [M]. 北京 : 科学出版社,2003 Wolf OE,Roy DP,Vermote E. MODIS Land Data Storage, Gridding,and ComPositing Methodology:level 2 Grid[J]. IEEE Transaetions on Geoseience and Remote Sensing,1998, 36(4):1 324-1 338

张怡, 硕士, 主要从事测绘工程及遥感应用研究。 第一作者简介:

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GEOSPATIAL INFORMATION

Index(Vol.11,No.3)

of low-altitude photogrammetry, and investigated the technical process of photogrammetry operations by using the system. Then it made the digital production test for the DLG, DEM and DOM. Finally, it made the accuracy assessment and feasibility analysis on the results. The results show that low-level image can be used for small areas of large-scale rapid topographic mapping. Key words low altitude aerial images, UAV, topographic mapping (Page:29) Read and Densi?cation Methods of IGS Precise Clock Offset File by LEI Yu Abstract In this paper, a subroutine program for reading a clock file with Fortran was compiled. Moreover, sleek Lagrange fitting was taken as a densification method to interpolate clock offset. Finally, results were discussed and analyzed. Key words International GNSS Service,precise clock offset,Lagrange interpolation,densification (Page:32) Realization of the Sunlight Azimuthal Orthographic Projection by ZHANG Kun Abstract There is a kind of map projection which shows sunlight in the map, thus established connection between map and date. The sunlight azimuthal orthographic projection maintains the circular outline of the Earth, it is a“Sun’s eye view of the Earth”. Based on coordinate transformation, this paper provided a detailed implementation of the sunlight azimuthal orthographic projection, and provided the equation. Key words map projection,daytime hemisphere,sunlight,coordinate transformation (Page:34) Automatic Detection Handing Method of Spatial Conflict in Spatial Data Dynamic Updating by CHEN Minghui Abstract This paper focused on conflict detection and processing in spatial data dynamic updating, based on the analysis of the manifestation of spatial conflict, geographic entities and database space oriented mapping as the starting point, explored a detection method of spatial conflict and made a conflict detection model. Considering different types of space conflict, targeted treatment was given. Finally, a verification making by independent development system achieved good results and confirmed that the method of conflict detection and processing in this article was reliable. Key words spatial mapping,spatial conflict,automatic detection,conflict resolution (Page:37) Application of GIS in the Management and Planning of Drinking Water Safety by HOU Jingwei Abstract GIS technology has been applied to monitor and evaluate water quality, to forecast water consumption, to develop system for drinking water safety, to protect and plan water source. Artificial intelligence, 3S technology and other new technologies and new ways were used to meet the multi-dimensional simulation, emergency management, project planning of the drinking water safety in support of GIS, which achieve the organic integration between drinking water security and GIS technology. Key words GIS, drinking water safety,management,planning,application, prospect (Page:40) Spatial Data Interoperability Model Based on Oracle Spatial by YANG Wensen Abstract The paper gave an integration interoperability model based on Oracle Spatial, according to different requirement of interoperability, using spatial data storage characteristics of Oracle Spatial. It would both meet the efficiency requirement within the department and the wide adaptability requirement of external department. Key words spatial data interoperability, Oracle Spatial, GML (Page:43)

Design of the Management System for Urban Green Space Planning Based on Service GIS by ZHONG Guangrui Abstract This thesis elaborated the basic concept of service GIS. And taking the design of the management system for urban green space in Meizhou City as an example, it offered details on the design of system database, the service configuration release, main function and the realization of client port, etc. In the end, it showed the further study on the system. Key words service GIS, SOA, geographic information service, Web Service, urban green space (Page:45) Pre-processing Method of MODIS Data by ZHANG Yi Abstract There are differences about the contrast and brightness value among the remote sensing images because of the time, solar radiation and the atmosphere .It is must be preprocessed to have better analysis and evaluate. This paper used ENVI to pre-processing the MODIS data which around the Tianshan Road that to prepare for the following data analysis. It was including data geometric correction and matching cutting. Key words MODIS, ENVI, pre-processing (Page:49) Geometric Precision Correction Based on Web Mercator Projection and Its Accuracy Analysis by SUO Junfeng Abstract For the intuitive, free, time-sensitive characters, Google Earth satellite images has been gradually spread in the field of engineering. In order to provide train of thought and method for engineering practice using GE, this paper analyzed the GE projection type, geometric precision correction principle and methods, and discussed method of Web Mercator projection and GE Remote Sensing image correction using ArcGIS10.0 and ENVI 4.8 platform. Key words Google Earth, Web Mercator projection,geometric correction (Page:51) Study on Calibration and Test of Domestic Single Lair-Lidar Instrument by ZHANG Heng Abstract The principle of range and angle measurement of Lair-Lidar was analyzed to get the source of range error and angle error. Actual experiments were done on single instrument, and the theory of range and angle measurement as well as the regularity of the test data were taken into consideration to get the relevant correction parameters. Correspondent models were then respectively built to rectify the measurement and effects before and after correction were compared for the analysis of the accuracy of test data after correction. The results show that range and angle measurement accuracy of Lidar be increased to a certain degree. Key words Lair-Lidar,test of single instrument,precision analysis (Page:54) Dodging Method of Considering the Position Relationship Between Images by ZHOU Zhicheng Abstract This paper proposed a color balance algorithm based on moment matching, which maps mean value of the image and the mean square error to a given value on the basis of considering the position relationship between images. Moreover, it made gray scale mean and standard deviation of different regions approximately equal to the value, and eliminated the differences of hue and brightness between the images as well as images inside, as far as possible under the conditions of maintaining the original color of the image. Key words image dodging,color balance,moment matching (Page:57) In?uence of Altitude Error on GPS Baseline Reduction by GUO Zhongming Abstract This article described the theory and technology of GPS baseline reduction based on GPS adjustment data at first. And then it introduced the influence of altitude error on the reduction. At last it proposed a practical method to detect the distortion of side length.


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