Getting Started with MODIS Version 6 Vegetation Indices Data Part 2:
Using the Data Presented by the Land Processes Distributed Active
Archive Center or LP DAAC. This is part 2 of the “Getting
Started with MODIS Version 6 Vegetation Indices Data” video
series. This video will cover the Science Datasets or SDSs in each
MODIS Vegetation Indices file, the fill values and scale factor
for the data and how to apply it, how to visualize Vegetation Indices
using a color map, and how to find Vegetation Indices resources on the
LP DAAC website. The MODIS Vegetation Indices Version 6 products provide
consistent information about the greenness of vegetation on the
Earth’s land surface. This data product family provides two types
of vegetation indices, the Normalized Difference Vegetation Index (NDVI)
and the Enhanced Vegetation Index (EVI). NDVI is calculated using a
ratio of the Red and Near Infrared or NIR wavelengths, whereas EVI is
calculated using a ratio of the Red, NIR, and Blue wavelengths along with
other factors. In the NDVI healthy vegetation is shown as it absorbs
the visible light and reflects more of the near-infrared light whereas
unhealthy vegetation reflects more of the visible light and less of the
near-infrared light. The EVI layer is similar to NDVI but it also
reduces atmospheric influences and accounts for bare soil interference.
MODIS vegetation indices are measured between -1 and 1. NDVI values less
than 0.3 and EVI values less than 0.2 generally indicate a lack of green
vegetation, or barren areas. Higher vegetation indices values indicate
areas of dense green vegetation, such as fully developed forest or
crop canopies. MODIS Vegetation Indices products are distributed
as Hierarchical Data Format – or HDF files and the file name
contains “MOD13” indicating Terra MODIS observations or “MYD13” for
Aqua MODIS observations. Here is a visual representation of the data
stored within a single Terra MODIS Version 6 Monthly Vegetation Indices
1 kilometer Level 3 gridded product, MOD13A3, HDF file.
The HDF file for this product contains NDVI and EVI data, quality information,
four reflectance bands, information about angles of the sun and satellite,
and the day of the year. It is important to know that a scale factor must be
applied to the NDVI and EVI data values before you begin using the data.
To learn more about the specific scale factors, fill values, and valid ranges
for the various MODIS Version 6 Vegetation Indices product layers,
please see the DOI Landing Pages on the LP DAAC’s website at lpdaac.usgs.gov.
Once you have an understanding of these values you can work with and observe
each of the science datasets. Here is an example of an NDVI image
of central Mexico from August 12th to 27th, 2016, shown using the Terra
MODIS Version 6 16-day Vegetation Indices 250 meter level 3 tiled in
sinusoidal grid projection product, MOD13Q1. NDVI are available as a single
science dataset. A colormap can be used to better visualize variations in the
presence of vegetation. A colormap is an RGB assignment of colors to certain values.
A colormap can be added using most Geographic Information System or
GIS software. Here is the same NDVI image shown using a colormap. On this colormap
0.0001 to 0.3 is a color ramp ranging from light brown to dark brown.
A light to dark green color ramp is used for values from 0.3001 to 1.0.
Fill values are classified as blue. For examples of how MODIS Vegetation
Indices products can be used in scientific applications, visit the
LP DAAC website. The Publications table has relevant literature, the Data in
Action section has short stories about scientific applications, and the
E-Learning page has tutorials, presentations, and other product resources.
Thank you for watching this video. For more information on MODIS Version 6
Vegetation Indices data please visit the LP DAAC website at lpdaac.usgs.gov.