Getting Started with VIIRS Surface Reflectance Data Part 3

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Detailed Description

This video focuses on how to interpret quality information for Visible Infrared Imaging Radiometer Suite (VIIRS) Surface Reflectance data products created by the National Aeronautics and Space Administration (NASA). VIIRS is a sensor that flies on the Suomi National Polar-orbiting Partnership (S-NPP) satellite, which was launched as a partnership between the National Oceanic and Atmospheric Administration’s (NOAA) and NASA in October 2011. S-NPP NASA VIIRS Surface Reflectance data products are distributed by NASA’s Land Processes Distributed Active Archive Center (LP DAAC). Information about VIIRS Surface Reflectance quality information, including how to decode it and where to find additional information, is provided in this video. To learn more about VIIRS Surface Reflectance data, and other data products distributed by the LP DAAC, please visit https://lpdaac.usgs.gov/.

The LP DAAC is one of twelve NASA Earth Observing System Data and Information System (EOSDIS) DAACs. It is located at the United States Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center in Sioux Falls, South Dakota. The LP DAAC ingests, archives, processes and distributes NASA Earth science land processes data and information.

Details

Date Taken:

Length: 00:03:46

Location Taken: Sioux Falls, SD, US

Video Credits

Content created by Danielle Golon (Contractor to USGS EROS)

Transcript

Getting Started with VIIRS
Surface Reflectance Data Part 3:

Interpreting Quality Information.
Presented by NASA’s Land Processes

Distributed Active Archive
Center or LP DAAC.

This is part 3 of the “Getting
Started with NASA VIIRS Surface

Reflectance Data” video series.
This video will explain the

quality information associated
with the data, demonstrate how

to decode the quality information,
and highlight where to find more

information on the LP DAAC website.
NASA VIIRS data products are 

derived from data collected by
the VIIRS sensor onboard the

joint NOAA/NASA Suomi National
Polar-orbiting Partnership (S-NPP).

Each VIIRS Surface Reflectance
product is archived and distributed

in HDF-EOS5 files. Within each
file are State Quality Assurance

or State QA, Quality Control or QC,
layers, and Quality Flag layers

that provide users with information
regarding the usability and

usefulness of the data products.
The quality information, such as

cloud state and aerosol quantity,
is provided for individual

pixels within the data. The
quality information can also

be used to filter out lower
quality data.”

The data within the quality
layers are bit-packed, meaning

each data pixel contains an
integer value that must be

converted to a binary value
for interpretation. The

bit-string interprets various
parameters, as shown by this chart.

Here is an example of how to
break down a bit binary value

using the 1 kilometer State QA
layer for the S-NPP NASA VIIRS

kilometer level 3 gridded

VNP09A1 data product. This is
the integer value of one pixel

from the Surface Reflectance
State layer. Here is the value

after we convert it to a 16-bit
binary value. This can be done

using a calculator or conversion
tool.  Once you have the binary

value, the value can be
interpreted using the chart.

The bit-string is read from
right to left. For example,

the Cloud State bits parameter
maps to the first two bits,

Bit-No. 0-1, in the bit-string.
Its bit combination is ‘00’

which means the pixel’s Cloud
state is “clear”. The next bit,

Bit-No. 2, represent the Cloud
Shadow Its bit combination is 0,

which means there is
no cloud shadow.

More detailed information about
the State QA, Band QC, and how

to decode quality bits for each
product can be found in the

product User Guide and Algorithm
Theoretical Basis Document or ATBD.

These documents are available in
the “Documentation” section of

each Digital Object Identifier
(DOI) Landing Page. The User

Guide provides a more in-depth
and up-to-date explanation of

the product. The ATBD provides
descriptions of the algorithms

and calculations that are
fundamental to the product.

User Guides are updated for
each new product version,

while ATBD’s are not.
It is important to note

that changes to the VIIRS
Surface Reflectance quality

information were made to
forward processed data

beginning August 21, 2017.
The quality information for

data dated prior to August

Version 1.1 of the User Guide.
For data from August 21, 2017

to present please see
Version 1.6 of the User Guide.

Thank you for watching our video.
For more information on VIIRS

Surface Reflectance data,
please visit the LP DAAC website

at lpdaac.usgs.gov