Figure 1. location of the five SIR-A data strips: 
(1) St. Joseph, Mo., (2) Mobile, Al., (3) Tallulah, 
ia., (4) Louisville, Ky. and (5) Stirling, Co. 1 
Figure 2. An extract shewing settlements of the 
Baoding area in North China as recorded on 
the SIR-A image. 
4 RESULTS 
4.1 Detectability of human settlements 
It ~ is interesting to note that the detectability 
of human settlements from the SIR-A data varied 
considerably from region to region. A striking 
difference was observed if human settlements in 
the North China Plain were compared with those 
recorded on the five different United States 
strips. The human settlements in the North China 
Plain exhibited such strong backscatter that a 
complete range of them could be detected (Fig. 
2). Even the very small villages could be mapped 
without much trouble. A comparison with the 
1:250,000 scale topographical map for this part of 
China suggested near 100 percent success rate of 
detectability. It Is also noteworthy that these 
Chinese settlements are highly compacted and 
mostly walled in the past. The plain is so very 
flat that it is almost at sea level -- the danger 
of flooding was revealed by the levees built along 
the rivers which were readily visible from the 
images (Fig. 2). 
Figure 3. An extract from St. Joseph, Mo. strip. 
Note the variations in building density detectable 
in some settlements. 
Figure 4. An extract frean the Mobile, Al. strip. 
Note the city of Mobile is difficult to delineate. 
Notice aiso the bright return from the industrial 
area and the weak return frean the air fields. 
In contrast, the United States environment 
appeared to show a greater diversity and 
variability in the detection of human settlements 
from the SIR-A data (Figs 3-7 and Table 1). 
Tne settlements normally distinguished 
themselves by the very strong backscatter which 
may have been caused by the corner reflector 
effect of some structures. It has long been 
recognized that the orientation of the radar 
antenna in relation to the cultural features being 
imaged can affect the strength of the microwave 
backscatter, hence variations In the grey tone of 
the objects in the images (Bryan, 1979; Hardaway 
et al., 1982). It was noted that when linear 
features were oriented perpendicular to the radar 
beam very strong backscatter called cardinal 
effect occurred. Henderson and Amita (1930) also 
observed that settlement detectability was 
significantly influenced by radar azimuth angle on