MYD13Q1 v006

MODIS/Aqua Vegetation Indices 16-Day L3 Global 250 m SIN Grid


PI: Kamel Didan

Description

The Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) Vegetation Indices (MYD13Q1) Version 6 data are generated every 16 days at 250 meter (m) spatial resolution as a Level 3 product. The MYD13Q1 product provides 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 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.

Along with the vegetation layers and the two quality layers, the HDF file will have MODIS 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 (MOD09A1) 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 MYD13Q1 data product is available from the MODIS land team validation site.

Collection and Granule

Collection

Characteristic Description
CollectionAqua MODIS
DOI10.5067/MODIS/MYD13Q1.006
File Size~93 MB
Temporal ResolutionMulti-Day
Temporal Extent2002-07-04 to Present
Spatial ExtentGlobal
Coordinate SystemGeographic Latitude and Longitude
DatumN/A
File FormatHDF-EOS
Geographic Dimensions1200 km x 1200 km

Granule

Characteristic Description
Number of Science Dataset (SDS) Layers12
Columns/Rows4800 x 4800
Pixel Size250 m

Layers

SDS Name Description Units Data Type Fill Value No Data Value Valid Range Scale Factor
250m 16 days NDVI 16 day NDVI NDVI 16-bit signed integer -3000 N/A -2000 to 10000 0.0001
250m 16 days EVI 16 day EVI EVI 16-bit signed integer -3000 N/A -2000 to 10000 0.0001
250m 16 days VI Quality VI quality indicators Bit Field 16-bit unsigned integer 65535 N/A 0 to 65534 N/A
250m 16 days red reflectance Surface Reflectance Band 1 N/A 16-bit signed integer -1000 N/A 0 to 10000 0.0001
250m 16 days NIR reflectance Surface Reflectance Band 2 N/A 16-bit signed integer -1000 N/A 0 to 10000 0.0001
250m 16 days blue reflectance Surface Reflectance Band 3 N/A 16-bit signed integer -1000 N/A 0 to 10000 0.0001
250m 16 days MIR reflectance Surface Reflectance Band 7 N/A 16-bit signed integer -1000 N/A 0 to 10000 0.0001
250m 16 days view zenith angle View zenith angle of VI Pixel Degree 16-bit signed integer -10000 N/A 0 to 18000 0.01
250m 16 days sun zenith angle Sun zenith angle of VI pixel Degree 16-bit signed integer -10000 N/A 0 to 18000 0.01
250m 16 days relative azimuth angle Relative azimuth angle of VI pixel Degree 16-bit signed integer -4000 N/A -18000 to 18000 0.01
250m 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
250m 16 days pixel reliability Quality reliability of VI pixel Rank 8-bit signed integer -1 N/A 0 to 3 N/A

Product Quality

The "250m 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 "250m 16 days pixel reliability" layer are provided in Table 4 on page 15 and the "250m 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 MYD13Q1 known issues please refer to the MODIS Land Quality Assessment website.

Documentation

Using the Data

E-Learning

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

Highlights from the Literature: January to March 2018

Why Do Leaves Change Color?

Tools

Citation

DOI: 10.5067/MODIS/MYD13Q1.006

About the Image