the results obtained by 
theme of the paper. 
| a strip about 0.8 km x 
ing respectively. The 
and radar are shown in 
ly, while the difference 
|]. The ortho-rectified 
played in Figure 10. 
ibout 257 meters in the 
rs on the highest ridge 
DEM represents a bald- 
EM includes the trees, 
| ground. An interesting 
deep gravel quarry. 
o under-sampling - that 
the 15 meter threshold 
lator. The difference 
me buildings) in green, 
ops (« 2 meters) are in 
evident in the ORI of 
'rns as well as a village 
of these characteristics 
surface of Figure 11. In 
ind some crop types are 
hould be noted that the 
ack-scatter and hence of 
w crops (e.g., cabbage) 
' bright in the ORI but 
surface. On the other 
n both. 
e Statistics 
| Laser 
  
4m) | 
7 0.28 
6 0.34 
04 2.16 
e surface statistics for 
rttemberg data set 
  
  
  
nt surface conditions to 
on ‘A’ is interpreted as 
unknown), and ‘C’ is 
ation for the difference 
em in Table 3. 
small (- 100m x 100m) 
ition for the bald earth 
) that described as the 
example (and constant 
this project area). The 
area ‘B’, as would be 
on. The crop sample is 
bald-earth, and probably 
ower than the visible 
areas over the whole test 
ors of about 50 cm into 
  
  
  
t E r4 E trs 
| 3 — ied = - - — 
Figure 8: Laser DEM 
  
x 
    
  
mmmiglometers 7 
Figure 9: Radar DEM 
Mer ES 11 S ME 
il SE | 
Magni 
PSN RE RE II EP 
ze el 2 A = - 
«c Y E + : 
ser ; SRL [== = ms ; 2 a5 7 
emis 0 Pom EXT : i 
ED A iem : = 3 facts XT 
cas Be EDS a es 
Figure 11: Difference Surface (Radar minus Laser) 
  
  
   
the radar DEMs upon which the 30 cm noise floor is 
superposed. These systematic variations can be removed 
with control. 
The other note of interest is the forested area which 
shows an effective mean height of 21 meters and a 
variability of about 2 meters. This is a reflection of the 
relative uniformity of the forest sample. 
6.3 Denver, Colorado, USA 
The third example is with respect to the extraction of 
building heights in a non-core area of a large urban 
center. Modeling of urban areas usually concentrates on 
the urban core areas although these may represent only a 
small percentage of the total urban area of interest. 
Because of the narrow canyons in the core areas, 
characterized by very  densely-packed, high-rise 
structures, the modeling of buildings can most 
successfully be accomplished by use of sensors with 
near-vertical viewing geometry such as laser or photo. 
However, urban areas often are very extensive (hundreds 
to thousands of km?) typically with small core areas 
surrounded by mixtures of residential, industrial and 
recreation areas, suburban developments, etc. 
For many applications, it may be more cost- and 
schedule-effective to use radar-derived DEMs. 
However, one of the questions is the capability of radar 
to determine the heights of tall structures, such as 
apartment buildings, that exist in isolation or clusters 
outside the core areas. There are a number of radar- 
related issues associated with the radar response to high 
buildings, including shadowing, layover and other 
factors (Mercer and Gill, 1998, Gamba and Houshmand, 
1999). As a result, there is usually a significant loss of 
data in front of and behind (as defined by the radar 
viewing direction) tall buildings. This makes the 
detection of building heights problematic and motivates 
the work summarized here. 
The area chosen for analysis is Leetsdale in Denver, 
Colorado. A laser DEM was acquired from Eaglescan of 
a 1 square mile (2.5 km?) area which was created in 
1996. The data set received had been edited to remove 
vegetation, vehicles and other non-stationary objects. 
However, buildings remained in the laser data set, 
permitting comparison with radar response. Digital 
Ortho-Images produced by ImageScans, Denver, were 
also available and very useful despite the earlier 
acquisition date (1993). Preliminary results from a 
single data set were published in Mercer and Gill (1998). 
More recently, a series of acquisitions from similar and 
orthogonal viewing directions enabled a more extensive 
investigation. Work is ongoing and will be published 
elsewhere, but we summarize here a set of interim 
results. 
The study included a set of 17 high-rise buildings in 
Leetsdale as denoted in Figure 12. The buildings range 
in height from about 10 to 45 meters. The radar data 
summarized here include DEMs from four data sets 
denoted as m60 (1997), m130 (1998), m130 orthogonal, 
and m166 (1999). In the foregoing, ‘m’ refers to the 
mission number, and the bracketed date is the year of 
acquisition. Three of these sets had similar viewing 
directions (westward) while the fourth was orthogonal, 
viewing southward. Additionally, some of the data were 
re-processed with lower correlation threshold. 
  
Building Heights 
60.0 " xm mn 
    
   
lii m130 Normal 
Om130 LowCorr 
BE m130 Orthogonal 1 
C) m60 Normal 
Ci m166 Normal 
50.0 
5 
o 
WLaser 
Height (m) 
8 
o 
3 
o 
10.0 
0.0 
1:39 15 14 4 13 16 S 17 11 8 10 9 1 7 2 6 
Building Number 
Figure 12: Bar Chart of Building Heights in 
Leetsdale Test Area 
  
  
  
The maximum height was determined for each of the 17 
buildings in the laser DEM and in each of the radar DEM 
data sets described above. The method was first to 
determine a region at the base of each building which 
appeared to be representative of the ground elevation. 
The ground elevation was then subtracted from the