Modis植被指数说明

http://tbrs.arizona.edu/project/MODIS/index.php

modis产生两种植被指数产品：EVI和NDVI，全球1公里和500m分辨率16天的合成产品。

NDVI对叶绿素比较敏感，而EVI对冠层结构变化包括叶面积指数（LAI），冠层类型、植被相和冠层结构。这两种植被指数在全球植被研究中可以互相补充，并能改进植被变化检测和冠层物理参数的提取。

NDVi被认为是NOAA-AVHRR提取的植被指数的连续，利用modis数据能延长提供更长时期的额数据记录，AVHRR植被指数已经被应用于多个方面包括：饥荒的预警系统，土地覆盖分类，健康和流行病学，干旱监测，土地退化，森林破坏和大尺度的植被与气候的年际变化，增强性的植被指数EVI时一个优化的植被指数，提高了对高生物量区域的敏感性，并且通过对植被冠层背景信号的去耦合和大气效应的减少改进了植被监测能力。地球观测系统最基本的任务之一就是研究陆地植被在大尺度全球过程（目的时理解地球作为一个系统是如何发挥作用的）的角色，这就要求理解全球植被类型的分布以及她们的生物物理、结构属性以及时空变化，modis植被指数有利于回答下面几个问题：

1.全球生态系统是怎么变化的

2.全球的土地利用和土地覆盖发生了什么变化，它们又是如何变化的？

3.生态系统是如何影响并对全球环境变化和碳循环响应的。

modis标准植被指数包括两种，网格式的植被指数和带有统计数据的质量分析（QA）和输入的反射数据，目前生产了500m和1km两种分辨率的16天间隔数据，以及有限的250m分辨率的数据，一个更为粗糙的植被指数气候模型网格也被建立，但是分辨率是为25km的月产品。产品标识符如下：

MOD13Q1: 16-day 250m VI (high resolution/ limited production)

MOD13A1: 16-day 500m VI (high resolution/ globally produced)

MOD13A2: 16-day 1 km VI (standard resolution/ globally produced)

MOD13A3: Monthly 1 km VI (standard resolution/ globally produced)

MOD13C1: 16-day 25 km VI (coarse resolution (CMG)/ globally produced)

MOD13C2: Monthly 25km VI (coarse resolution (CMG)/globally produced)

modis植被指数数据产品以tile为基本单位，其投影方式为integerized sinusoidal (ISIN) grid投影。植被指数是以L2每天的表面反射率产品(MOD09 series)，反射率产品经过了分子散射，臭氧吸收，以及气溶胶校正，最后合成16天的250/500m 或者1km植被指数产品，其中1km植被指数产品需要将250m和500m数据像元利用'MODAGAGG'算法规划到1km。植被指数产品包含了许多SDS（science data sets）：16天的NDVI,EVI值，16天的NDVI,EVI的质量评估（QA），剩余的红（band1）近红（band2），中红（band6）以及蓝（band3）的反射产率，卫星高度，太阳高度以及相对的方位角，250mEVI利用到了500m分辨率的去除气溶胶效应的蓝波段

数据信息

覆盖范围：全球，

处理级别：3，

时空特征：250m，500m，1km和25km16天和每月间隔，

主要应用：生态系统监测和变化监测，碳平衡，水文学，

产品类型：标准

以下为英文原文

Two MODIS VIs, the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI), are produced globally over land at 1 km and 500 m resolutions and 16-day compositing periods. Whereas the NDVI is chlorophyll sensitive, the EVI is more responsive to canopy structural variations, including leaf area index (LAI), canopy type, plant physiognomy, and canopy architecture. The two VIs complement each other in global vegetation studies and improve upon the detection of vegetation changes and extraction of canopy biophysical parameters. modis The MODIS NDVI is referred to as the "continuity index" to the existing 20+ year NOAA-AVHRR derived NDVI time series, which could be extended by MODIS data to provide a longer term data record for use in operational monitoring studies. The AVHRR-NDVI has been widely used in various operational applications, including famine early warning systems, land cover classification, health and epidemiology, drought detection, land degradation, deforestation and in relating large-scale interannual variations in vegetation to climate. The enhanced vegetation index (EVI) is an 'optimized' vegetation index with improved sensitivity in high biomass regions and improved vegetation monitoring through a de-coupling of the canopy background signal and a reduction in atmosphere influences.

Key Science Questions

One of the primary interests of the Earth Observing System (EOS) program is to study the role of terrestrial vegetation in large-scale global processes with the goal of understanding how the Earth functions as a system. This requires an understanding of the global distribution of vegetation types as well as their biophysical and structural properties and spatial/temporal variations. The MODIS VI products aid in answering several key EOS questions including:

How are global ecosystems changing?
What changes are occurring in global land cover and land use, and what are their causes?
How do ecosystems respond to and affect global environmental change and the carbon cycle?

The MODIS standard VI products include two, gridded vegetation indices (NDVI, EVI) and quality analysis (QA) with statistical data that indicate the quality of the VI product and input reflectance data. They are currently produced at 16-day intervals at 500m and 1km resolutions with limited production at 250 m resolution. A coarser, climate modeling grid (CMG) version of the VI products at a resolution of 25 km are also in development, as are monthly versions of all the VI products. The products are labeled as:

MOD13A1: 16-day 500m VI (high resolution/ globally produced)
MOD13Q1: 16-day 250m VI (high resolution/ limited production)
MOD13A2: 16-day 1 km VI (standard resolution/ globally produced)
MOD13A3: Monthly 1 km VI (standard resolution/ globally produced)
MOD13C1: 16-day 25 km VI (coarse resolution (CMG)/ globally produced)
MOD13C2: Monthly 25km VI (coarse resolution (CMG)/globally produced)

For production purposes the MODIS VIs are output in tile units that are approximately 1200km by 1200km in the integerized sinusoidal (ISIN) grid projection. When mosaicked, all tiles cover the terrestrial Earth and the MODIS VI can be generated globally each 16 days. The VI products rely on the level 2 daily surface reflectance product (MOD09 series), which are corrected for molecular scattering, ozone absorption, and aerosols. The VI algorithms ingest the level 2G (gridded) surface reflectances and temporally composite these to generate the 16-day, 250/500m or 1km VI products. The 1 km VI product (MOD13A2), however, requires aggregation of 250m and 500m MODIS pixel sizes to 1km by way of the 'MODAGAGG' algorithm. The VI output file contains a variable number of 'Science Data Sets' (SDS) that include the 16-day NDVI and EVI values; the 16-day QA for NDVI and EVI; the residual red (band 1), near-infrared (band 2), middle-infrared (band 6), and blue (band 3) reflectances; and view zenith, solar zenith, and relative azimuthal angles from the selected, composited pixels. There is some production of the 250m MODIS VI products (MOD13Q1) over a limited set of tiles. The 250m EVI currently uses a disaggregated 500m blue band for aerosol resistance. The 250m VI products are planned to be in full production and globally available

Description of the "Compositing Algorithm".

Additional Information

Coverage: Global
Processing Level: 3
Spatial/ Temporal Characteristics: 250m, 500m, 1km, and 25km at 16-day and monthly compositing intervals.
Key Science Applications: Ecosystem monitoring and change detection; Carbon balance; Hydrology
Product Type: Standard, at-Launch
The Algorithm Theoretical Basis Document (ATBD), MODIS Vegetation Indices, is available for viewing.
The MODIS Vegetation Index Product Users' Guide is available for viewing.