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AN EVALUATION ON THE DATA QUALITY OF SRTM DEM AT THE ALPINE AND 
PLATEAU AREA, NORTH-WESTERN OF CHINA 
Y. Liu 
School of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000 -liuy@lzu.edu.cn 
Commission I, Technical Session: ThS-3 
KEY WORDS: DEM, Shuttle Radar Topographic Mission (SRTM), evaluation, Inferometric SAR (InSAR), land cover, topographic 
effect 
Abstract: 
This paper evaluates the quality of SRTM3 data for alpine and plateau areas in Northwestern (NW) China against DEM data 
extracted from topographic maps. These SRTM data were obtained from both the ESRI ArcGIS 9.2 software package and NASA's 
Jet Propulsion Laboratory website. It shows that these two data sources provide the approximate precision as the DEM based on 
1:250000 scale topographic maps in general. In our study area, the ESRI SRTM data have about 38% of raster units with less than 
10m absolute elevation error, 58%; <20m, 90%; <49m, 95%; <65m, 99%; <92m, and 99.9%; <143m compared with the topographic 
maps. The delta surface void filling process conducted on the ESRI SRTM data does not change the error scheme of the total DEM. 
In relatively low and flat basins, as well as the wide valleys on the plateau, the absolute elevation error is typically less than 5m. 
Significant errors of more than tens or hundreds of meters were obtained in rugged mountainous areas, even lakes and reservoirs in 
low land. Furthermore, the author suggested that the slope of terrain has no effect on the error, while the northern slope has higher 
minus mean error compared with the southern one. At last, elevation errors in glacial, deciduous forest and desert settings present a 
normal Gaussian distribution with all the peaks at -20 to 0m, and few raster units with absolute errors of more than 100-200m. 
1. INTRODUCTION 
A lack of suitable topographic data has long been an obstacle to 
the study of the environment, especially for most developing 
countries. New remote sensing technologies have now begun to 
change this situation. During an 11 day flight in February 
2000, the Space Shuttle Endeavor conducted the Shuttle Radar 
Topographic Mission (SRTM), a large-scale survey that 
collected interferometric radar topography data between 56°S 
and 60°N latitude. As the first set of continuous data covering 
most of the earth's surface, it overcomes the deficiencies of 
conventional maps that have a variety of scales and levels of 
precision around the world, the problems associated with 
country-specific ellipsoid model and coordinate systems, the 
inconsistencies that often occur at national boundaries, and 
even the lack of data. 
The SRTM data can be freely downloaded from NASA's Jet 
Propulsion Laboratory website. There are two resolutions of 
SRTM data at this website, one is 1 arc second for US 
(SRTM1), and another one is 3 arc seconds for the rest of the 
world (SRTM3). But there are voids about 0.25% of the total 
area in these data (Farr, et al. 2007). ESRI Inc. has supplied 
void-filled SRTM data since 2006 when releasing his new 
version ArcGIS 9.2. It is therefore more convenient for use. 
The importance of SRTM data for the environment study has 
been widely recognized (Rabus, 2003). Previously, many 
applications did not evaluate data quality'. Other studies for 
evaluating data quality are still being conducted, but most are 
concerned with study areas located at low elevations and few 
have examined alpine settings, although the reports were 
satisfactory. A NASA report discloses that there are widespread 
and large elevation errors associated with SRTM data at the 
margin of the Qinghai-Tibet Plateau (Rodriguez, et al., 2005). 
Consequently, it is necessary to evaluate the SRTM data in this 
area before it is used further in studies. The rugged nature and 
large size of this region make it well suited for such an 
evaluation study as the alpine and plateau area of Northwestern 
China has high relief, multi-genetic geomorphic landforms and 
a variety of landscapes. This study evaluated two aspects of 
data quality for elevation: geographic location and altitude. 
2. DATA PREPARATION 
2.1. Study area characteristics 
The study area is located between 96-102°E longitude and 
36-40°N latitude (Figure 1). It corresponds to a full 1:1000000 
Figure 1. Map of study area