MODIS转换工具包（MCTK）用户指南

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"The MODIS Conversion Toolkit (MCTK) User’s Guide 是一份详细的用户手册，由 Devin A. White 编写，提供了在 ENVI 环境下使用 MCTK 进行 MODIS 数据转换的图文步骤和编程代码。该指南涵盖了从安装到实际操作的各个层面，并特别对比了 MCTK 输出与 MRT 和 MRT Swath 的差异。" 本文档主要介绍了如何利用 MCTK（MODIS Conversion Toolkit）处理和转换 MODIS 数据，包括交互式和程序化的方式，以及支持的 MODIS 产品列表和处理工作流程。以下是详细内容： II. 安装部分会指导用户如何下载和安装 MCTK，可能涉及设置环境变量、配置路径以及确保兼容的 ENVI 版本等步骤。 III. 对于项目化和重投影的 MCTK 输出与 MRT 及 MRT Swath 的比较，这部分会讨论两者在数据格式、空间分辨率和坐标系统上的差异，帮助用户理解 MCTK 转换后的数据特点。 IV. 交互式在 ENVI 中转换 MODIS 数据部分，分为四个子章节： A. Level 1A 未校准辐射数据：介绍如何使用 MCTK 将原始 MODIS 1A 数据转换为可用的形式。 B. Level 1B 校准辐射数据：详细说明如何处理经过大气校正的 MODIS 1B 数据。 C. Level 2 Swath：涉及对 MODIS 2 级条带数据的处理，可能包括大气纠正和地表反射率计算。 D. Level 2/3/4 Grid：这部分将介绍如何处理更高层次的格网数据，如植被指数和水体探测等。 V. 程序化在 ENVI 中使用 MCTK 转换 MODIS 数据，这部分包含 API 调用语法和示例代码，帮助程序员实现自动化处理流程，提高效率。 A. API calling syntax 部分将详细解释 MCTK 提供的函数接口，包括参数说明和返回值类型。 B. Examples 部分提供实际的代码示例，展示如何在用户的应用程序或脚本中调用这些 API。 VI. 支持的 MODIS 产品列表会列出 MCTK 能够处理的所有 MODIS 传感器的产品，包括 Terra 和 Aqua 卫星的不同波段和产品类型。 VII. MODIS Conversion Toolkit Processing Workflow Diagram 展示了 MCTK 的处理工作流程图，帮助用户理解数据从输入到输出的整体过程。 MCTK 是一个强大的工具，它为 MODIS 数据用户提供了一套完整的解决方案，从数据获取、预处理到高级分析，涵盖了 MODIS 数据处理的多个阶段。这份用户指南是学习和使用 MCTK 的宝贵资源。

The MODIS Conversion Toolkit User’s Guide

Figure 2. A “blank” instance of MCTK. The various fields and sections will update with

information and options that are relevant to the supplied MODIS product. To ensure that

you have the most recent version of MCTK, check the displayed version number.

To select where converted data should be placed, click on the Output Path button and select a

folder. The folder where the input file resides is chosen by default. You must also provide a

rootname for the outputted data. The string value you choose will be used as the first part of

longer filenames automatically built by the tool during the conversion process. Since multiple

files can be generated by a single conversion process, it is useful to choose an intuitive and

descriptive rootname so data from the same input file can be easily grouped afterwards.

Note: With the exception of Level 1A datasets, all converted data produced by MCTK is stored

in single precision floating point—regardless of original data type. This is done to store

converted data in as few files as possible and, in general, does not result in any loss of

precision. The exceptions are Quality Assurance / Quality Control (QA/QC) datasets, which can

lose some precision during conversion. For those datasets, it is recommended that you set the

“Use Double Precision” option to Yes. After conversion, recast the QA/QC data back to its

original type (e.g., unsigned long integer) prior to examining individual bits.

A. Level 1A Uncalibrated Radiance

When a Level 1A Uncalibrated Radiance file is provided as input, you will be presented with

several processing options. On the right side, you will see the four datasets stored inside of the

HDF that contain image data at three spatial resolutions (250m, 500m, and 1000m). MCTK

The MODIS Conversion Toolkit User’s Guide

recognizes the fact that there are multiple resolutions within the file and displays them in the

metadata window under Pixel Size. You can choose to output any combination of the available

datasets, but each will be placed in a separate file due to how they are processed by the tool.

Each output file will contain appropriate band number designations and wavelength values.

After clicking on Process, you will see two ENVI progress bars: one related to the conversion of

the current dataset and one related to the overall conversion process.

The tool also recognizes that Level 1A data does not contain georeferencing information

(indicated by the Native Projection being set to None in the metadata viewer). However, if you

have access to the related Geolocation product (MOD03/MYD03), you can use it to project the

Level 1A data. To do so, select Projected or Standard and Projected under Output Type and

then click on Input Geolocation File. You will be prompted to supply an appropriate file. A filter

is provided to aid you in finding the correct product and the current Level 1A filename will show

up in the title bar of the file selection dialog. In order to proceed, the second, third and fourth

sections of the Level 1A filename and geolocation filename have to match. For example, a

Level 1A file with the name “MYD01.A2006007.0300.005.2007078081622.hdf” requires a

geolocation file with the name “MYD03.A2006007.0300.005.2006125230829.hdf.” If the

supplied filenames do not match, the projection options section will be greyed out and you will

not be allowed to proceed with the conversion. If the filenames do match, the most appropriate

UTM zone for the supplied data is automatically calculated and made available (Figure 3).

Please note that for scenes in polar regions, Universal Polar Stereographic (UPS) will be

selected instead. Standard resampling methods (Nearest Neighbor, Bilinear, and Cubic

Convolution) are available. Bowtie correction is performed automatically. Output pixel size is

automatically determined based on product type and dataset. For projections that do not use

meters, the meter-based pixel size is automatically converted to one that is appropriate. You

also have the option of providing your own fill value to use during the conversion process and

your own background value to use during the projection process. The default value for both is 0.

If a value less than zero is provided, zero is used instead. Note: An alternative pixel size can

be provided through the programmatic interface.

Filenames for converted data

For Level 1A files, two types of filenames are possible. They are constructed as follows:

 Rootname + Dataset Name + Raw_DN.img (unprojected data)

 Rootname + Dataset Name + Raw_DN_georef.img (projected data)

A Note on Output Type

Because MCTK is a conversion utility, you will always receive at least one ENVI format file as

output. If you choose to output projected data using the Projected or Standard and Projected

option, two sets of output files will be generated. The first set is unprojected (Standard) and is

used to create the second set (Projected). The difference between the two options is that when

you choose Projected, the first set of files (Standard) is deleted once the projection process is

complete.

A Note on Projecting 250m Data

In order to perform bowtie correction on 250m data, you must change your Image Tile Size in

the ENVI Preferences dialog (under Miscellaneous) to a value of at least 10.0 MB. If this is not

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