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ASTER GDEM 2 README
ADVANCED SPACEBORNE THERMAL EMISSION AND
REFLECTION RADIOMETER (ASTER)
GLOBAL DIGITAL ELEVATION MODEL (GDEM) VERSION 2
October 2011
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EXECUTIVE SUMMARY
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)
Global Digital Elevation Model (GDEM) is concurrently distributed from the Ministry of
Economy, Trade, and Industry (METI) Earth Remote Sensing Data Analysis Center
(ERSDAC) in Japan and the National Aeronautics and Space Administration (NASA)
Earth Observing System (EOS) Data Information System (EOSDIS) Land Processes
(LP) Distributed Active Archive Center (DAAC) in the United States.
Version 2 is produced with the same gridding and tile structure as Version 1.
Improvements over version 1 include the use of additional scenes to improve coverage,
a smaller correlation kernel to yield higher spatial resolution, and an improved water
mask.
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CONTENTS
Executive Summary ................................................................................................................. ii
Contents ................................................................................................................................... 3
List of Tables and Figures ....................................................................................................... 3
Introduction .............................................................................................................................. 4
ASTER GDEM Characteristics ................................................................................................ 5
Basic GDEM Characteristics .................................................................................................. 5
GDEM Package ..................................................................................................................... 5
QA File Description ................................................................................................................ 6
GDEM Validation Summary ..................................................................................................... 9
Disclaimer ................................................................................................................................. 9
Use Constraints ....................................................................................................................... 9
User Services ..........................................................................................................................10
Acronym List ...........................................................................................................................11
LIST OF TABLES AND FIGURES
Figure 1 ASTER GDEM File Structure ....................................................................................... 6
Table 1 ASTER GDEM Characteristics ...................................................................................... 5
Table 2 Anomaly Replacement Sources .................................................................................... 8
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INTRODUCTION
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on
the National Aeronautic and Space Administration (NASA) spacecraft Terra is capable
of collecting in-track stereo using nadir- and aft- looking near infrared cameras. Since
2001, these stereo pairs have been used to produce single-scene (60- x 60-kilometer
(km)) digital elevation models (DEM) having vertical (root-mean-squared-error)
accuracies generally between 10- and 25-meters (m). On June 29, 2009, NASA and the
Ministry of Economy, Trade, and Industry (METI) of Japan released a Global Digital
Elevation Model (GDEM) to users worldwide at no charge as a contribution to the
Global Earth Observing System of Systems. This “Version 1” ASTER GDEM (GDEM
1.0) was compiled from over 1.2 million scene-based DEMs covering land surface
between 83 degrees (°) north (N) and 83° south (S) latitudes. GDEM 1.0 is a 1 arc-
second elevation grid divided and distributed as 1° x 1° tiles.
A joint U.S.-Japan validation team assessed the accuracy of GDEM 1.0, augmented by
a team of 20 cooperators selected through an Announcement of Opportunity. In
summary, GDEM 1.0 was found to have an overall accuracy of around 20-m at the 95
percent (%) confidence level. The team also noted several artifacts associated with poor
coverage, cloud contamination, water masking issues, and the stacking process used to
produce GDEM 1.0 from individual scene-based DEMs (ASTER GDEM Validation
Team, 2009). An independent horizontal resolution study estimated the effective spatial
resolution of GDEM 1.0 to be on the order of 120-m.
NASA and METI released a second version of the ASTER GDEM (GDEM 2) in mid-
October, 2011. GDEM 2 has the same gridding and tile structure as GDEM 1.0, but
benefits from the inclusion of additional scenes to reduce artifacts, higher horizontal
resolution using a smaller correlation kernel (5 x 5 versus 9 x 9 used for GDEM 1.0),
and an improved water mask. Also, a 5-m overall bias observed in GDEM 1.0 was
removed in the newer version. GDEM 2 has an overall accuracy of around 17-m at the
95% confidence level, and a horizontal resolution on the order of 75-m.
