Getting Started with MODIS V6 Surface Reflectance Data Part 3

Video Transcript
Download Video
Right-click and save to download

Detailed Description

Getting Started with MODIS Version 6 Surface Reflectance Data Part 3: Interpreting Quality Information This video focuses on the National Aeronautics and Space Administration’s (NASA) Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) Version 6 Surface Reflectance data distributed by NASA’s Land Processes Distributed Active Archive Center (LP DAAC). Information about MODIS Surface Reflectance quality information, including how to decode it and where to find additional information, will be provided. To learn more about MODIS Version 6 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: 00:04:58

Location Taken: Sioux Falls, SD, US

Video Credits

Script and content created by Danielle Golon, Innovate, Inc.! for the NASA LP DAAC

Transcript

Getting Started with MODIS
Version 6 Surface Reflectance

Data Part 3: Interpreting
Quality Information.

Presented by the Land Processes
Distributed Active Archive

Center or LP DAAC.
This is part 3 of the “Getting

Started with MODIS Version 6
Surface Reflectance Data”

video series. This video will
cover the associated Quality

information for the data,
including the quality science

dataset layers and their decoded
quality bits, tools that provide

users with information about
Quality, and where to find out

more information on the
LP DAAC’s website.

Each MODIS Version 6 Surface
Reflectance product contains

data packaged in Hierarchical
Data Format (HDF) files.

Within each HDF file are
several Quality Assurance (QA)

science datasets (SDS) that
provide users with clues

regarding the usability and
usefulness of the data products.

The quality information can also
be used to filter data based on

levels of quality. There are
several types of QA information

that can come with the MODIS
Version 6 Surface Reflectance

data products. The Reflectance
Band Quality Assurance QA or

Quality Control QC and Coarse
Resolution QA provide information

on the quality of atmospheric
correction at the pixel level

and provide information on Band
Data Quality. The data state QA

and Coarse Resolution State QA
flags provide information about

each pixel’s state that might
compromise the pixel’s information,

for example the presence of clouds.
This type of QA is specifically

about the pixel and is independent
from information about the quality

of the SDS or resolution. More
detailed information about specific

QA information for each product can
be found in the product User Guide

and Algorithm Theoretical Basis
Document (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 and 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.

The QA science dataset layers
are binary encoded and bit-packed.

Meaning each pixel in the QA layer
contains an integer value that

must be converted to a bit 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

Terra MODIS 8-Day Surface
Reflectance 500 meter level 3

gridded MOD09A1 data product.
Here is the decimal value of one

pixel from the 500 meter
Reflectance Band Quality this

number will convert to this 32-bit
binary value. This can be done using

a calculator or conversion tool.
Once the binary value is found,

the value can be interpreted using
the chart. The bit-string is read

from right to left. For example,
the Bit-Word for Bit-No. 0-1 is 01

which means the corrected product
produced at less than ideal

quality – some or all bands.
Bit-No. 2-5 or the Band-1 Data

Quality is identified using the
Bit-Word 0000, which means these

bands are highest quality.
To aid in unpacking and interpreting

the bits, the Land Data Operational
Products Evaluation (LDOPE) facility

has developed the LDOPE QA
“unpack_sds_bits” tool, which can be

executed from the command line or
invoked via scripts.

The unpack_sds_bits tool decodes
requested bit fields and writes

them to an output HDF file containing
a new SDS that can be viewed with

software supporting the HDF or
HDF-EOS data formats.

More information about the LDOPE Tools
can be found under the “Tools”

section of the LP DAAC website.
Another tool that can be used to view

the QA information is the Application
for Extracting and Exploring Analysis

Ready Samples (AppEEARS).
This application allows users to view

the Modland QA bits,
based on the date, product, layer,

and coordinates of data points of
interest. AppEEARS also provides users

with fully decoded MODIS quality
information in a .csv file.

For more detailed materials about
Surface Reflectance Quality

Information visit the E-Learning
page on the LP DAAC website.

Search for “QA” in the table to
learn more.

Thank you for watching our video.
For more information on MODIS Version

6 Surface Reflectance data please
visit the LP DAAC website

at lpdaac.usgs.gov.