利用LDOPE工具解码MODIS陆地产品质量信息

MODIS 十余种陆地产品都包含像元尺度的质量评估信息(QA),这些信息是用户合理利用这些产品的基础。由于QA类型多但数值小,通常是把多个QA以二进制格式压缩成整型数据的一个波段,这样节省了归档空间,加快了网络传输,并期望用户使用MODIS陆地数据业务化产品质量评估工具包( LDOPE Tools)把压缩的二进制恢复为通常的十进制波段。但是,由于LDOPE是由25个独立的软件组成的工具包,并没有按照特定功能进行组合,使得LDOPE普及受到限制,导致大量具有潜在应用价值的QA未能得到应有的开发利用。以MODIS 森林覆盖率产品中的一个QA(云量,Cloud)为例,介绍了把二进制恢复为十进制的主要过程,包括:①识别MODIS陆地产品中与QA相关的科学数据集；②LDOPE和 MRT软件安装；③利用LDOPE的3个命令进行QA的提取、解码、地图投影恢复；④利用MRT对解码后QA进行地图投影和文件格式转换；⑤利用ENVI对QA进行地理定位与属性验证。经过上述处理,QA即可与MODIS陆地产品进行像元尺度的综合分析。

Study on Decoding MODIS QA Using LDOPE Tools

Every MODIS Land Product includes Quality Assessment (QA) which that provides pixel level quality information in order to achieve an informed application.However,QA are stored in a packed bit layer,which is good to save space yet bad to input it into traditional image processing systems.This paper explored major steps to decode packed QA for MODIS Vegetation Continuous Filed,using LDOPE tools,induding(1) Understand QA-related Scientific Data Set (SDS) based on specific MODIS land product,“cloud” for current case study;(2) Installations of LDOPE and MRT;(3) Mosaic,unpack,and restore QA in LDOPE,two ways were tested-single file and multiple file;(4) Map re-projection and file reform in MRT;(5) Validate geo-location and QA attribute in ENVI.Through above processing,QA will be analyzed with relevant MODIS land products in pixel level.