Getting Started with MODIS Version 6 Surface Reflectance
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 Surface
Reflectance Data” video series. This video will cover what
“Surface Reflectance” means, Aqua and Terra MODIS surface
reflectance data products, the scale factor of the data
and other data values, and various MODIS band combinations.
Surface reflectance is the amount of light reflected by
the surface of the Earth. MODIS surface reflectance data
products provide an estimate of the surface spectral reflectance
from the ground, with atmospheric correction.
Surface reflectance is a unit less ratio of surface radiance
to surface irradiance with a value that typically falls
between 0.0 and 1.0. MODIS Version 6 Surface Reflectance
products are distributed as Hierarchical Data Format –
or HDF files. The HDF files contain all the science datasets
or SDS for the MODIS data product. The Digital Object
Identifier or DOI Landing Page for each MODIS Version 6 Surface
Reflectance product lists all of these science datasets under
the Data Layer Characteristics table. The science datasets will
differ between the MODIS Version 6 Surface Reflectance products.
However, most MODIS Version 6 Surface Reflectance products
will contain seven surface reflectance bands.
The seven MODIS surface reflectance bands have a
spectral range from 459 to 2155 nanometers. Here is a
visual representation of the science datasets stored within
a MOD09A1 HDF file. MOD09A1 is the Terra MODIS Version 6 8-Day
Surface Reflectance 500 m level 3 gridded product.
The HDF file for this product contains 7 surface reflectance
bands, quality information, information about angles of
the sun and satellite, and the day of the year.
If your research involves calculations of MODIS Version
6 Surface Reflectance data, it is important to know that a
scale factor must be applied to the data before you complete
your calculations or work with the data. For MODIS Version 6
surface reflectance products a scale factor of 0.0001 should be
applied to the seven surface reflectance bands, resulting in
data values typically between 0 and 1. Data values that fall
outside this range are considered fill values. The other science
dataset in the HDF file have either a scaling factor of 0.01
or do not have a scaling factor. Users can apply a scale factor to
their data via a data script recipe, through manual calculation,
or in a geographic information system (GIS) program.
To learn more about specific scale factor, fill values,
and valid ranges for the various MODIS Version 6
Surface Reflectance products please see the DOI Landing
Pages on the LP DAAC’s website at lpdaac.usgs.gov.
Stacking the surface reflectance bands in different combinations
can emphasize different aspects of the Earth’s surface.
Today we will demonstrate three band combinations using the
MOD09A1 product. Band stacking can be done using several programs.
Today we will show you how to stack bands using Multispec, a free program
that allows users to interactive with and analyze remote sensing data.
The band combination 1-4-3 creates a true color image and is a
representation of how the human eye would see the area.
Here is a view of part of Europe using the 1-4-3 band combination.
Vegetation is shown as green, the snow in the Alps is white,
and the barren areas are tan or brown.
Another band combination is 3-6-7, which highlights snow and ice.
Here is the same location shown using the 3-6-7 band combination.
In this band combination the snow in the Alps is shown as red,
ice in clouds as light pink, clouds are white, water is shown
as a dark red, vegetation is green, and deserts are a light blue-green color.
The third band combination, 7-2-1, is used to observe burn scars on
the Earth’s surface from fires. This band combination is especially
useful in areas that have a lot of wildfires throughout the year.
For example, the Western United States, shown here, had a lot of fires in 2016.
Using the 7-2-1 band combination we can see some of the burn scars
from these fires. Here is the same Terra MODIS image enlarged and
reprojected to Universal Transverse Mercator (UTM) for a better view of
the burn scars in California. In the 7-2-1 band combination burn
scars are shown as red to reddish-brown, vegetation is green,
desert or other naturally bare soil is a pink, and water is black or
dark blue. For examples of how MODIS Surface Reflectance products can be
used in scientific applications, visit the LP DAAC website.
The Publications 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 our videos. For more information
on MODIS Version 6 Surface Reflectance data please visit the LP DAAC
website at lpdaac.usgs.gov.