maximum elevation to determine the maximum height 
in each case. 
In Figure 12, a bar chart shows the radar in terms of 
ascending building heights. All of the results are shown 
for each building, referenced to the laser height which is 
presumed to be ‘truth’. Of the 17 buildings, 14 show 
quite good consistency with respect to the laser truth. 
Two of the buildings (#2 and #12) have anomalously low 
heights which are correctly recovered upon re-processing 
with reduced correlation threshold (‘LowCorr’). At 
present, only one data set (‘Orthogonal’) for one building 
(#5) shows anomalous height without reason and is being 
investigated. Excepting these ‘outliers’, the associated 
regression graph (not shown here) indicates a typical 3 
meter RMS variability among the radar-only heights; the 
radar-derived heights tend to be about 2 meters lower 
than the laser-derived heights again with a scatter of 
about 3 meters RMS. There is a trend (not yet 
confirmed) for the uncertainty to grow with height but to 
maintain a variability of about 10% of height. 
7. CONCLUSIONS 
In this paper we have presented the argument that laser- 
and radar-derived DEMs are complementary for a 
variety of applications. The major virtues of the laser 
systems are that they have finer vertical accuracy (15 to 
30 cm RMS depending on conditions), they can 
penetrate tree canopies (particularly in  leaf-off 
condition), and because of near vertical geometry, they 
can acquire information in dense urban cores. 
Comparatively, the major advantages of interferometric 
SAR (as demonstrated by STAR-3i) are price (3 to 10 
times lower than laser) and delivery, enabling DEMs of 
large areas to be acquired with similar grid spacing but 
reduced vertical accuracy. 
In support of the foregoing arguments, the performance 
of STAR-3i was demonstrated in two non-urban 
examples and one urban example: 
(1) In the two non-urban areas, it was demonstrated that 
STAR-3i, in its standard operating mode, exhibits an 
elevation noise floor of about 30 cm (10) at similar 
sample spacing to the laser. Systematic errors in the 
STAR-3i DEMs, which manifest themselves over larger 
areas and are usually project-specific, can be removed to 
some level by the use of ground control. In the examples 
shown here, the systematic error component was at the 
50 to 70 cm level, although in some projects it is higher. 
(2) In the urban example, it was demonstrated that in 
non-core areas, building heights can be extracted using 
STAR-3i with an uncertainty of about 10% of the 
building height over a height range of 10 to 45 meters. 
The implication is that laser should be used in areas 
where its unique characteristics are required and that 
radar can be effectively used over larger areas with 
reduced accuracy as a trade-off for significantly reduced 
cost and earlier delivery. 
  
   
ACKNOWLEDGMENTS 
We gratefully acknowledge the following providers of BY 
data used in this study. The laser-derived DEMs for the 
three examples were provided respectively by: Mr. 
Stephen DeLoach of  EarthData Technologies, 
Hagerstown, MD (the Red River data), by Dipl. Ing. 
Andreas Schleyer of the Landesvermessungsamt, 
Karlsruhe, Germany (the Baden-Wurttemberg data), and 
by Mr. Robert Eadie of EagleScan Inc., Denver, CO (the 
Denver urban data). Digital ortho-images of the Denver, 
Leetsdale area were created by ImageScans, Denver, and 
the Red River checkpoints were provided by Mr. James 
Garster of the US Army Topographic Engineering 
Center (TEC). We would also like to thank our Intermap 
colleagues in the airborne radar group and in the 
processing group for providing the STAR-3i data and for 
helpful discussions. 
  
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