Getting Started with NASA’s Visible Infrared Imaging
Radiometer Suite or VIIRS 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 NASA
VIIRS Surface Reflectance Data” video series. This video will
cover what “Surface Reflectance” means, the types of VIIRS
Surface Reflectance products distributed by the LP DAAC,
the scale factor of the data and other data values, various
VIIRS band combinations, and how to find VIIRS Surface
Reflectance resources on the LP DAAC website. Surface
reflectance can be described as the amount of light reflected
by the surface of the Earth. VIIRS surface reflectance data
are estimates of surface reflectance in each of the VIIRS
reflective bands. Surface reflectance is a unitless ratio
of surface radiance to surface irradiance with a value that
typically falls between 0.0 and 1.0.
VIIRS Surface Reflectance products are distributed as
Hierarchical Data Format – Earth Observing System 5 –
or HDF-EOS5 files. The file name contains the shortname,
“VNP09”. Here is a visual representation of the data
stored within a single file for the VIIRS Daily Surface
Reflectance Level 3 gridded product, VNP09GA. The file
for this product contains information about the satellite,
the sun angles, the Surface Reflectance bands, quality
information, and information about the satellite observations.
It is important to know that before you begin using the data,
a scale factor must be applied to Surface Reflectance data values.
For VIIRS Surface Reflectance products a scale factor of 0.0001
should be applied to the Surface Reflectance bands, resulting in
data values typically between 0 and 1. Data values that fall
outside this range are considered fill values. To learn more about
the specific scale factors, fill values, and valid ranges
for the various Surface Reflectance 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.
Stacking, or compositing, the surface reflectance bands
combines the band wavelengths to emphasize different aspects
of the Earth’s surface. Specific bands are assigned to the Red,
Green, and Blue portions of the image. Today we will demonstrate
three band combinations using the 1 kilometer layers of the
VNP09GA product. Band stacking can be done in most types of
Geographic Information Systems (GIS) software. The band
combination M5-M4-M3 creates a true color image and is a
representation of how the human eye would see the area.
Here is a view of the Northwestern United States using
the M5-M4-M3 band combination. Vegetation is shown as green,
the snow and clouds as white, and the barren areas are tan
or brown. Another band combination is M3 - M10 - M11,
which highlights snow and ice. Here is the same location
shown using the M3 -M10 - M11 band combination. In this band
combination snow is shown as red, ice in clouds as light
pink, clouds are white, water is shown as a dark red,
vegetation as green, and deserts are a light blue-green
color. A third band combination, M10 – M7 – M5,
is used to show Natural Color. This band combination
exaggerates natural colors, making it easier to
differentiate between land features. In this image
vegetation is shown as bright shades of greens, land as
shades of brown, clouds and water are shown as shades
of blue. For examples of how VIIRS Surface Reflectance
products can be used in scientific applications,
visit the LP DAAC website. The E-Learning page has
tutorials, presentations, and other product resources
related to the VIIRS Surface Reflectance data.
Stayed tuned for future Data in Action and Publications
using VIIRS data! Thank you for watching our video.
For more information on VIIRS Surface Reflectance
data please visit the LP DAAC website at lpdaac.usgs.gov