Full text: Advances in the quality of image data

States (Table 2). Because a compact city with smaller plots and closely spaced buildings represents 
high spatial frequencies, the resolution requirements for urban studies of China are much greater than 
those for the United States (Figure 5; Welch, 1982). This is further confirmed by comparing the 
current and anticipated IFOVs for various satellite sensor systems with the average urban parcel sizes 
in different countries (Figure 6). 
Table 2. Relative Sizes for Urban Built-up Areas of 50,000 to 500,000 Population. 
  
  
  
  
  
  
  
  
  
  
COUNTRY RELATIVE SIZE 
United States 1.0 
Canada 0.60 
Sweden 0.15 
Japan 0.11 
China 0.03 
A^ U.S. IFOV 
80m 
+ 
PARCEL 
ox 
z US 
o Sy 
> CANADA so 
  
  
  
SPATIAL FREQUENCY 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
1 CHINA 39 
SWEDEN 
5 JAPAN 20 
a 15 
> CHINA 10 
P1 
— 
SPATIAL FREQUENCY ii 
Figure 5. Representative spatial frequencies Figure 6. Comparison of urban land parcel 
of urban land parcels in the United size with the IFOV's of satellite 
States and China (Welch, 1982). sensor systems (Welch, 1982). 
It is generally accepted that a minimum of about four IFOV/pixel sized units are required to 
adequately represent a parcel (Figure 7). The intersection of the horizontal line representing four 
IFOV/pixel units with the curves in Figure 7 defines the threshold IFOV or resolution requirements for 
a sensor system designed to permit urban land use mapping at the parcel level. From this figure it 
appears that IFOVs of 30, 25, 15, 10 and 5 m, are required to map urban land use in the United States, - 
Canada, Sweden, Japan and China. These values, -although approximations, do indicate the variable mm 
spatial resolution requirements for different geographic areas. - 
  
  
  
       
Ye p———— eT CT 
IFOV'S OR PIXELS/PARCEL 
u 
   
  
  
    
le À 1 
o 5 10 15 20 25 30 35 40 45 50 ss so 6 7 75 
IFOV OR PIXEL DIMENSION (m) 
Figure 7. Number of IFOVs contained within representative urban land 
parcel sizes as a function of IFOV (or pixel) dimension 
(Welch, 1982). 
It is of interest to note that a land use classification system has been developed in the United 
States which groups land use classes into four successively finer levels of detail based on the sensor 
data available for compilation (Anderson et al., 1976). By calculation, the resolution levels (IFOV) 
required to extract land use information for the classes in Level I, II, III and IV categories are 
approximately 80, 2, 1 and 0.5 m, respectively (Figure 8). These values, which are based on long 
empirical experience, indicate that spatial resolutions of better than 5 m IFOV are required to 
construct land use maps depicting Level II (or finer) class information. Interestingly, although 
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