206 
seen in Figure 1, each of the data takes overlapped in one limited area, but each also 
recorded relatively extensive areas of terrain (i.e.. Data Take 97.4--8484 sq. km.; Data 
Take 93.2--4148 sq. km.; and Data Take 45.2--7600 sq. km.). A changing and varied 
mixture of forest and field landscape patterns, topography, and numerous settlements in a 
northern boreal forest environment comprised the study area for this investigation. 
METHODOLOGY 
The 1:500,000 master positive transparencies (first generation) of the imagery were 
optically enlarged (2X to 8X) and all sites thought to be settlements were recorded on 
transparent overlays. The overlays were then registered to maps at a scale of 1:200,000. 
For purposes of this study, "settlements" were defined as all clusters of 4 or more 
structures and dwellings indicated by individual structure symbols and/or designated by 
placename on the 1:200,000 topographic maps. 
Errors of omission and commission were tabulated and their locations noted on the 
maps. In some instances topographic maps at scales of 1:100,000 and 1:50,000 were also 
consulted for error source identification. The spatial patterns of errors and correct 
identifications were examined by referring to and comparing the radar imagery, overlays 
and maps. Field work was also conducted be traversing approximately 75 per cent of the 
entire study area and noting site and causes of errors. 
After preliminary analysis of all three data sets (but prior to error analysis) a second 
interpretation was completed using only Data Takes 45.2 and 97.4. As these two sets 
slightly overlapped and ran almost perpendicular to each other (see Figure 1) the purpose 
was to compare the effect of incidence angle and look direction over similar terrain and 
topographic conditions. In this instance, only those areas comprised of forested hills and 
mountains with intervening meadow areas were included. That is, this simple landscape 
pattern reduced the environmental variables in the data set. The simplified environment 
allowed a comparison of the effect of look direction with regard to terrain slopes and an 
examination of detectability under conditions where the high specular return of settlement 
structures in open areas and clearings would provide high contrast to the uniform 
medium-to-dark gray surrounding forest cover and fields. 
ANALYSIS AND RESULTS 
The results of the interpretation of the three SIR-B data takes are found in Table II. 
It is apparent that Pass 2 (Take 93.2) with the smallest angle of incidence (15.7 degrees) 
was the poorest image in terms of percent detection (44.9 %) and in absolute 
accuracy--27.7% (i.e., the greatest number of commission errors). The steep incidence 
angle of this pass produced a great many specular returns from non-settlement targets 
including road intersections, some hill slopes, quarries, and open water/wetland areas. 
These results were the exact opposite of that reported by Sieber and Hartl (1986). 
However, the present study incorporated a much larger sample size and study area and 
concentrated only on settlement detection.