Getting Started with NASA's Visible Infrared Imaging
Radiometer Suite or VIIRS Surface Reflectance Data
Part 1: All About Accessing Data. Presented by the Land
Processes Distributed Active Archive Center or LP DAAC.
This video is part 1 of the "Getting Started with NASA's
VIIRS Surface Reflectance Data" video series. This
video will provide information about the NASA
VIIRS satellite sensor, the NASA VIIRS Surface
Reflectance data products and how to search for and
download these data using NASA's Earthdata Search
Client data access tool. The VIIRS satellite sensor
is one of five instruments on-board the Suomi National
Polar-orbiting Partnership (S-NPP) satellite. S-NPP was
launched on October 28, 2011 and is the first in a series
of four Joint Polar Satellite System (JPSS) satellites.
VIIRS is part of a collaborative mission between
the National Oceanic and Atmospheric Administration
(NOAA) and NASA. NASA is applying algorithms similar
to the algorithms used in Moderate Resolution Imaging
Spectroradiometer (MODIS) data to the NASA VIIRS data.
NASA VIIRS data are considered a continuation of
the MODIS data, just as MODIS data are a continuation
of Advanced Very High Resolution Radiometer
(AVHRR) data. VIIRS observes the entire Earth's surface
twice each day from a polar orbit at 824 kilometers or
512 miles above the Earth's surface. The 3,000 kilometers
swath width of the VIIRS instrument, which is 710
kilometers greater than that of MODIS, allows for
no gaps in coverage, similar to those observed in MODIS
near the equator. The VIIRS instrument provides 22
spectral bands at two spatial resolutions,
375 meters and 750 meters, which are resampled to
500 meters, 1 kilometer, and 5,600 meters in the
NASA produced data products to promote consistency with
the MODIS heritage. The LP DAAC distributes four
different types of VIIRS Surface Reflectance products.
These include two Daily VIIRS Surface Reflectance
products and two 8-Day Surface Reflectance
products. All data distributed by the LP DAAC
are available for download at no charge. VIIRS data
are distributed as Hierarchical Data Format –
Earth Observing System 5 or HDF-EOS5 products.
The VIIRS Surface Reflectance products are
level 3 products, meaning they have been
atmospherically corrected, gridded into a map
projection, and temporally composited. The daily
Surface Reflectance products are available as a
0.05 degree or 5,600 meter Global Climate Modeling Grid
or CMG and as a 1 kilometer or 500 meter tiled product
in sinusoidal projection, based on the MODIS sphere.
The 8-day Surface Reflectance products are available as
1 kilometer and 500 meter tiled products also in
sinusoidal projection. Data products are available
from January 19, 2012 to present. Detailed information
about each of the individual products can be found on the
LP DAAC website at lpdaac.usgs.gov. The surface
reflectance data are created by adjusting top-of-atmosphere
reflectance to compensate for atmospheric effects.
Corrections are made for the effects of molecular gases,
including ozone and water vapor, and for the effects
of atmospheric aerosols. The VIIRS Surface Reflectance
products contain two different types of Surface Reflectance
Bands. The M indicates bands with a nadir resolution of
750 meters, which are resampled to 1 kilometer.
The I indicates bands with a nadir resolution of 375
meters, resampled to 500 meters. The M bands are
only in the VIIRS surface reflectance products that
provide 1 kilometer spatial resolution, including the
8-Day VNP09A1 product and the Daily VPN09GA product.
Likewise, the I bands are only in the VIIRS surface
reflectance products that provide a 500 meter spatial
resolution, including the 8-Day VNP09H1 product and
the Daily VNP09GA product. The Daily Climate Modeling
Grid VNP09CMG product contains both the I and M
bands but at a 0.05 degree or approximately 5,600
meter spatial resolution. The VIIRS Surface
Reflectance products contain bands that are in a spectral
range that is similar to the MODIS Surface Reflectance
bands, but not exact. The LP DAAC website also offers
several ways to download VIIRS Surface Reflectance
data products. At the bottom of the DOI Landing
Page for each product are links to useful data access
tools. In this video, downloading data using NASA's
Earthdata Search Client data access tool will be
demonstrated step-by-step. The Earthdata Search home
page can also be accessed from the Tools section of
the LP DAAC website. From the Earthdata Search
home page, search.earthdata.nasa.gov,
click on the "Earthdata Login" button to login
with your NASA Earthdata account. If you do not
have an Earthdata account, click on the register
button and follow the prompt to create one.
Now, search for the VIIRS Daily Surface Reflectance
1 kilometer and 500 meter level 3 gridded product,
VNP09GA. Type "VNP09GA" in the search bar and
hit enter. Click on the VNP09GA data product.
This will pull up all of the VNP09GA granules.
Parameters for a specific time and location can be
set above the map. For this video let's look at
the Daily Surface reflectance for the United
States City of Portland, Oregon during the summer
of 2012. First, pan and zoom the map to Portland.
Change the temporal range by clicking on the temporal
icon and then click on the Start date and change the
date to "June 20, 2012." Now, change the End date
to "September 21, 2012" and click on apply filter.
To change the spatial information, click on
the spatial icon and select "rectangle" from
the drop down menu. Draw a rectangle around
Portland. You will now see green outlines that
indicate the footprint of the VIIRS tiles
contained in your rectangle. The granules from 2012 that
are located in the selected area are now listed in the
white box at the bottom of the page. Above the granule
list are options to "Download Data" which allows
a user to download all of the matching granules,
an "i" icon to learn more about the data collection,
a filter icon to further filter the data, and a plus
sign icon, which allows a user to add multiple data
products to their Earthdata Search project. Click on the
first box containing a scene in the bottom white box to
select the most recent scene. This box contains a preview
of the granule, the VIIRS filename, the dates of the
data, an "x" in the upper right hand corner to remove
the scene from your granule list, an "i" for more
information, and the retrieval icon to download
a single granule. Click on the "i" icon to bring up
the metadata for the selected granule. Remember,
metadata are data about data. The metadata include
the DOI, which is necessary for proper citation, as
well as information on the scene's corner coordinates,
input granules, and more. Click on the "Metadata" tab
for links to download metadata in different
standard formats. Click on "Back to Granules" to return
to the granule list. Click on "Download Data" to
download all of the granules in the granule
list. Now, review the data download order on the
"Data Access" page, this page lists the number of
granules in the order and the size of the order.
From here users can select the service options.
Select "Direct Download" to instantly receive the
granules in the order or select "Stage for Delivery"
to receive the granules via email. Click on
"submit" or "continue" and then "submit" to
submit the order. Depending on the data access method,
the data can be accessed immediately or will be sent
to the user via email.
Thank you for watching our video. For more
information on NASA's VIIRS Surface Reflectance data
please visit the LP DAAC website at lpdaac.usgs.gov
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