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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
In the final step of the investigations, a semivariogram of the 
elevation anomalies was calculated for every AOI. This was 
done using the Geostatistical Analyst Toolbox, a part of the 
ArcGIS 9.3 GIS software package. Using this toolbox, the 
magnitude of anisotropy was calculated for each airport. The 
value of anisotropy was than mapped against the average value 
of look angle. It was found that both variables are uncorrelated. 
Similar results have been obtained for the look direction. A 
most likely reason is that the majority of the SRTM elevations 
have been obtained through averaging of elevations calculated 
from a few data takes. This probably caused cancellations of the 
directional characteristics of the elevation anomalies. 
4. CONCLUSIONS 
The main aim of this project was to develop circumstantial 
evidence linking the presence of outliers in the SRTM data sets 
with the presence of anthropogenic structures. We have chosen 
airports as objects of interest because they usually contain large 
and well-defined anthropogenic structures. But the presented 
conclusions may be also applicable to other similar objects, 
including large car parks, tall buildings, large metallic sheds, 
and others. This study allows us to infer the following 
conclusions: 
1. There is tangible evidence that large anthropogenic 
structures cause elevation anomalies in the SRTM data. 
2. Attempts to relate elevation anomalies to both look angle 
and look direction did not provide conclusive evidence of 
a relationship between the independent variables (LA and 
LD) and the dependent variable (the anomalies). This is 
most probably caused by the mitigation strategy deployed 
by the SRTM system (averaging elevations from a few data 
takes). 
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3. A comprehensive study of the original complex radar data 
takes used to develop interferograms over the AOIs is 
recommended. Such a study should be aimed at identifying 
a mathematical model explaining the mechanism causing 
the undesired effects, and propose a modification of the 
InSAR data processing chain over areas suspected to be 
causing the artefacts in the InSAR-derived DEMs. 
5. REFERENCES 
API, 2011. Aeronautical Information Publication. United States 
of America. 21st Ed. Dep. of Transportation Federal Aviation 
Administration. 
Becek, K., 2008. Investigating error structure of shuttle radar 
topography mission elevation data product. Geophys. Res. 
Lett., 35, L15403, do1:10.1029/2008GL034592. 
GEDTF, 2010. Global Elevation Data Testing Facility. 
http://gedtF.org (29 Dec. 2011). 
JPL, 2008. SRTM Coverage Plotting Tool. 
http://space.jpl.nasa.gov/cgi-bin/wtdb (29 Dec. 2011). 
NASA, 2001. Shuttle Radar Topography Mission. The Mission 
to Map the World. http://www2.jpl.nasa.gov/srtm/ (29 Dec. 
2011). 
Rodríguez, E., Morris, C. S., Belz, J. E., Chapin, E. C., Martin, 
J. M., Daffer, W. and Hensley, S., 2005. An assessment of the 
SRTM topographic products. Tech. Rep. JPL D-31639, 143 pp., 
Jet Propul. Lab., Pasadena, Calif.