An Assessment of the SRTM Topographic Products - Jet Propulsion ...

Chapter 1
Overview
The Shuttle Radar Topography Mission (SRTM) [1] was a collaboration between the National Aeronautics
and Space Administration (NASA) and the National Imagery and Mapping Agency (NIMA).
[NIMA changed its name in November 2003 to the National Geospatial-Intelligence Agency (NGA).]
SRTM collected interferometric radar data which has been used by the Jet Propulsion Laboratory
(JPL) to generate a near-global topography data product for latitudes smaller than 60 ◦ . As part of
the SRTM mission, an extensive ground campaign was conducted by NIMA and NASA to collect
ground-truth which would allow for the global validation of this unique data set.
The purpose of this report is to document the analysis that was undertaken to verify the SRTM
performance and to show how the mission requirements were met and exceeded. Table 1.3 presents
a summary of the SRTM performance for each mapped continent. This performance exceeded the
required performance by almost a factor of 2. Other assessments of the SRTM performance have
examined the spatial resolution of SRTM [2], or compared its performance against lidar for vegetated
regions [3]. Unlike those studies, we will endeavor to characterize all components of the SRTM errors
on a global basis.
In this chapter, we review the SRTM measurement requirements, review the ground-truth data
used for the instrument verification, and summarize the characteristics of the residual errors. The
remaining chapters of this report present the details showing how summary numbers were derived.
Chapter 2 shows in detail all comparisons made to verify that SRTM was meeting the most fundamental
requirement on height accuracy. Chapter 3 studies in greater detail the different spatial
components in the residual SRTM errors, and looks in some detail at the long wavelength errors.
Chapter 4 concentrates on the high-frequency error components and validates the Terrain Height
Error Data (THED) product put out by SRTM. This chapter also presents the random and absolute
errors included as part of the SRTM height data headers. Chapter 5 details the methodology used to
calibrate the system timing and geolocation and verifies the geolocation accuracy using radar identifiable
kinematic GPS transects. Finally, Chapter 6 presents a detailed comparison of the SRTM
DEM against a high resolution and accuracy DEM obtained by the GeoSAR interferometer, allowing
a cross-comparison of interferometric data sets.
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