MYD13A2 v006

MODIS/Aqua Vegetation Indices 16-Day L3 Global 1 km SIN Grid


PI: Kamel Didan

Description

The MYD13A2 Version 6 product provides Vegetation Index (VI) values at a per pixel basis at 1 kilometer (km) spatial resolution. There are two primary vegetation layers. The first is the Normalized Difference Vegetation Index (NDVI), which is referred to as the continuity index to the existing National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR) derived NDVI. The second vegetation layer is the Enhanced Vegetation Index (EVI), which has improved sensitivity over high biomass regions. The algorithm for this product chooses the best available pixel value from all the acquisitions from the 16 day period. The criteria used is low clouds, low view angle and the highest NDVI/EVI value.

Provided along with the vegetation layers and the two quality assurance (QA) layers are reflectance bands 1 (red), 2 (near-infrared), 3 (blue), and 7 (mid-infrared), as well as four observation layers.

Characteristics

Improvements/Changes from Previous Versions

  • The 16-day composite VI is generated using the two 8-day composite surface reflectance granules (MYD09A1) in the 16-day period.
  • This surface reflectance input is based on the minimum blue compositing approach used to generate the 8-day surface reflectance product.
  • The product format is consistent with the Version 5 product generated using the Level 2 gridded daily surface reflectance product.
  • A frequently updated long-term global Climate Modeling Grid (CMG) Average Vegetation Index product database is used to fill the gaps in the CMG product suite.

Product Maturity

Validation at stage 3 has been achieved for all MYD13 vegetation products. Further details regarding product validation for the MYD13A2 data product is available from the MODIS land team validation site.

Collection and Granule

Collection

Characteristic Description
CollectionAqua MODIS
DOI10.5067/MODIS/MYD13A2.006
File Size~9 MB
Temporal ResolutionMulti-Day
Temporal Extent2002-07-04 to Present
Spatial ExtentGlobal
Coordinate SystemSinusoidal
DatumN/A
File FormatHDF-EOS
Geographic Dimensions1200 km x 1200 km

Granule

Characteristic Description
Number of Science Dataset (SDS) Layers12
Columns/Rows1200 x 1200
Pixel Size1000 m

Layers

SDS Name Description Units Data Type Fill Value No Data Value Valid Range Scale Factor
1 km 16 days NDVI 1 km 16 days NDVI NDVI 16-bit signed integer -3000 N/A -2000 to 10000 0.0001
1 km 16 days EVI 1 km 16 days EVI EVI 16-bit signed integer -3000 N/A -2000 to 10000 0.0001
1 km 16 days VI Quality VI quality indicators Bit Field 16-bit unsigned integer 65535 N/A 0 to 65534 N/A
1 km 16 days red reflectance Surface Reflectance Band 1 N/A 16-bit signed integer -1000 N/A 0 to 10000 0.0001
1 km 16 days NIR reflectance Surface Reflectance Band 2 N/A 16-bit signed integer -1000 N/A 0 to 10000 0.0001
1 km 16 days blue reflectance Surface Reflectance Band 3 N/A 16-bit signed integer -1000 N/A 0 to 10000 0.0001
1 km 16 days MIR reflectance Surface Reflectance Band 7 N/A 16-bit signed integer -1000 N/A 0 to 10000 0.0001
1 km 16 days view zenith angle View zenith angle of VI Pixel Degree 16-bit signed integer -10000 N/A 0 to 18000 0.01
1 km 16 days sun zenith angle Sun zenith angle of VI pixel Degree 16-bit signed integer -10000 N/A 0 to 18000 0.01
1 km 16 days relative azimuth angle Relative azimuth angle of VI pixel Degree 16-bit signed integer -4000 N/A -18000 to 18000 0.01
1 km 16 days composite day of the year Day of year VI pixel Julian day 16-bit signed integer -1 N/A 1 to 366 N/A
1 km 16 days pixel reliability Quality reliability of VI pixel Rank 8-bit signed integer -1 N/A 0 to 4 N/A

Product Quality

The "1 km 16 days VI Quality" layer is stored in an efficient bit-encoded manner. The unpack_sds_bits executable from the LDOPE Tools is available to the user community to help parse and interpret the quality layer.

In addition to data access and transformation processes, AppEEARS also has the capability to unpack and interpret the quality layers.

The QA bit flags for the "1 km 16 days pixel reliability" layer are provided in Table 4 on page 15 and the "1km 16 days VI Quality" in Table 5 on page 16 of the User Guide.

In areas where no valid VI is retrieved, VI Quality bits 11-13 are correctly assigned to indicate the land/water type. The other bits are set to 1 which can create a false notion of the parameter description; however, since no valid VI is retrieved these values can be ignored.

Known Issues

The following issues have been detected:

  • Unexpected missing data in the last cycles of each year.
  • Incorrect instances of "NoData" and spikes in NDVI values.
  • VI Usefulness Bits are not correctly assigned.

For instances where the VI Quality (bits 0-1) is flagged as good and the VI Usefulness (bits 2-5) indicates the same pixels have the lowest usefulness score, users are advised to disregard the usefulness score.

Corrections will be implemented in Collection 6.1 reprocessing in 2019.

For complete information about the MYD13A2 known issues please refer to the MODIS Land Quality Assessment website.

Documentation

Using the Data

E-Learning

R You Ready to Python? An Introduction to Working with Land Remote Sensing Data in R and Python

Using AppEEARS Quality Service to Extract Information from MODIS Quality Layers

Getting Started with MODIS Version 6 Vegetation Indices Data Part 1: All About Accessing Data

Getting Started with MODIS Version 6 Vegetation Indices Data Part 2: Using the Data

Getting Started with MODIS Version 6 Vegetation Indices Data Part 3: Interpreting Quality Information

Data In Action

Sensing Our Planet: NASA Earth Science Research Features 2016

Tools

Citation

DOI: 10.5067/MODIS/MYD13A2.006

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