nsation 
rnal of 
fication 
ccuracy 
try and 
ensional 
levation 
sing, 54 
n DEM 
sactions 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B4, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
SUMMARY OF THE VALIDATION OF THE SECOND VERSION OF THE ASTER 
GDEM 
D. J. Meyer ^, *, T. Tachikawa ", M. Abrams ©, R. Crippen 5, T. Krieger ?, D. Gesch *, C. Carabajal * 
* US Geological Survey, Earth Resource Observation and Science Center, Sioux Falls, SD, USA — (dmeyer, 
gesch)@usgs.gov 
? Earth Remote Sensing Data Analysis Center, Tokyo, Japan — tatikawa@ersdac.or.jp 
"Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA — (mabrams, 
robert.e.crippen)@jpl.nasa.gov 
* US National Geospatial Intelligence Agency, St. Louis, MO, USA — Tabitha.L.Krieger@nga.mil 
‘Sigma Space Corp, NASA Goddard Space Flight Center, Greenbelt, MD, USA— Claudia.C.Carabajal@nasa.gov 
Commission VI, WG VI/6 
KEY WORDS: ASTER, Global Digital Elevation Model, Accuracy, DEM/DTM, Comparison, Geodesy, Global-Environmental- 
Databases, Land Cover, Mapping, Satellite 
ABSTRACT: 
On October 17, 2011, NASA and the Ministry of Economy, Trade and Industry (METI) of Japan released the second version of the 
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM) to users 
worldwide at no charge as a contribution to the Global Earth Observing System of Systems (GEOSS). The first version of the 
ASTER GDEM, released on June 29, 2009, was compiled from over 1.2 million scene-based DEMs covering land surfaces between 
83°N and 83°S latitudes. The second version (GDEM2) incorporates 260,000 additional scenes to improve coverage, a smaller 
correlation kernel to yield higher spatial resolution, and improved water masking. 
As with GDEMI, US and Japanese partners collaborated to validate GDEM2. Its absolute accuracy was within -0.20 meters on 
average when compared against 18,000 geodetic control points over the conterminous US (CONUS), with an accuracy of 17 meters 
at the 95% confidence level. The Japan study noted the GDEM2 differed from the 10-meter national elevation grid by -0.7 meters 
over bare areas, and by 7.4 meters over forested areas. The CONUS study noted a similar result, with the GDEM2 determined to be 
about 8 meters above the 1 arc-second US National Elevation Database (NED) over most forested areas, and more than a meter 
below NED over bare areas. A global ICESat study found the GDEM2 to be on average within 3 meters of altimeter-derived control. 
The Japan study noted a horizontal displacement of 0.23 pixels in GDEM2. A study from the US National Geospatial Intelligence 
Agency also determined horizontal displacement and vertical accuracy as compared to the 1 arc-second Shuttle Radar Topography 
Mission DEM. US and Japanese studies estimated the horizontal resolution of the GDEMO2 to be between 71 and 82 meters. Finally, 
the number of voids and artifacts noted in GDEMI were substantially reduced in GDEM2. 
1. INTRODUCTION latitudes, cloud contamination, water masking issues and the 
stacking process used to produce the GDEMI from individual 
The ASTER instrument on NASA's Terra spacecraft collects in- scene-based DEMs (ASTER GDEM Validation Team, 2009). 
track stereo using nadir- and aft looking near infrared cameras. Two independent horizontal resolution studies estimated the 
These stereo pairs are used to produce single-scene (60 x 60 effective spatial resolution of the GDEMI to be on the order of 
km) digital elevation models having vertical (root-mean- 120 meters (Crippen, 2009; Tachikawa et al. 2009). 
Squared-error) accuracies generally between 10 m and 25 m. On 
  
  
June 29, 2009, NASA and METI released a Global Digital 
Elevation Model (GDEM) to users worldwide at no charge as a 
contribution to the Global Earth Observing System of Systems 
(GEOSS). This “version 1” ASTER GDEM (GDEMI) was 
compiled from over 1.2 million scene-based DEMs covering 
land surfaces between 83°N and 83°S latitudes. GDEMI is a 1 
arc-second elevation grid distributed as 1°-by-1° tiles. 
A joint US-Japan validation team assessed the accuracy of the 
GDEMI, augmented by a team of 20 cooperators selected 
through an Announcement of Opportunity (AO). In summary, 
the GDEMI was found to have an overall accuracy of around 
20 meters at the 95% confidence level. The team also noted 
several artifacts associated with poor stereo coverage at high 
  
* Corresponding author. 
NASA and METI released a second version of the ASTER 
GDEM (GDEM2) on October, 17, 2011. The GDEM2 has the 
same gridding and tile structure as GDEMI, but benefits from 
the inclusion of 260,000 additional scenes to improve coverage, 
a smaller correlation kernel (5x5 versus 9x9 for GDEMI) 
yielding higher spatial resolution, and improved water masking. 
Also, a negative 5 meter overall bias observed in the GDEMI 
was removed in newer version. As with the GDEMI, the 
GDEM2 validation was the joint responsibility of U.S. and 
Japanese partners. The U.S. validation team included the U.S. 
Geological Survey (USGS), NASA’s Jet Propulsion Laboratory 
(JPL), the National Geospatial-Intelligence Agency (NGA) and 
the NASA Goddard Space Flight Center (GSFC). The Japanese 
validation was conducted by the Earth Remote Sensing Data