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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BI. Istanbul 2004 
  
combined into an overall estimate for the cross scan or along 
scan component via a weighted least squares with the weights 
being set to the reciprocal of the variance estimate for each 
individual measurements. All error estimates presented in this 
section are lo values. Along scan MTF results are presented in 
Figure 7; cross scan MTF results are presented in Figure 8. 
Cross Scan MTF 
  
  
  
  
  
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Normalized Frequency 
Figure 7. OV-3 panchromatic cross scan MTF estimate 
Along Scan MIF 
  
  
  
  
  
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0.0 0.1 0.2 2.3 0.4 0.5 
Normalized Frequency 
Figure 8. OV-3 panchromatic along scan MTF estimate 
The MTF of imaging systems are frequently specified by the 
MTF value at the Nyquist frequency, where the along scan and 
cross scan components are averaged. For OV-3 imagery without 
sharpening, the overall Nyquist MTF was measured as 0.10 + 
0.01. With the nominal sharpening applied to the imagery, the 
overall Nyquist NTF was measured as 0.15 + 0.01. 
Individual MTF measurements at the Nyquist frequency for the 
cross scan and along scan components are presented in Figure 
9. The Nyquist MTF measurement samples are ordered such 
that the fixed target edges and urban edges are grouped 
together. The overall data point on the graph is the weighted 
least squares of all the fixed target and urban edge 
measurements, with the dashed horizontal line indicating the 
overall mean value for reference. 
Cross Scan Nyquist MTF Measurements 
  
  
  
  
  
  
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Along Scan Nyquist MTF Measurements 
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Edge Measurement Index 
Figure 9. OV-3 cross scan and along scan Nyquist MTF 
measurement samples 
4. DISCUSSION 
Consistent results were obtained across the range of edges used 
for analysis. This is demonstrated by the Nyquist MTF values 
presented in Figure 9. Significant overlap in the lo confidence 
intervals is observed. Note also that the confidence in the urban 
edges, as derived from the simulated edge experiment, is higher 
than for the fixed targets. This is primarily driven by the line 
length of the edges used. Even though the edge contrast was 
typically less for the urban edges used in this analysis compared 
to the fixed targets, the urban edges were much longer, which 
decreased the error estimate. 
The Nyquist MTF for the unsharpened panchromatic band of 
0.10 x 0.01 provides a balance between aliasing in the imagery 
due to high MTF and poor image sharpness due to low MTF. 
The sharpening processing that is applied to the imagery 
provides a modest boost in sharpness while not introducing 
objectionable artifacts. 
Ultimately, MTF is one component in characterizing the overall 
image quality performance of an imaging system. Other 
components include signal to noise ratio and radiometric 
accuracy. These parameters for the OV-3 sensor are published 
in the literature (Kohm, 2004) and must be considered in 
determining overall image quality and comparing quality 
metrics between different sensors. 
5. CONCLUSIONS 
A robust method for estimating the MTF of high resolution 
remote sensing systems is presented. Error estimates for cach 
measurement point are determined using simulations of edges 
with a wide range of characteristics. Along scan and cross scan 
MTF results for the OrbView-3 panchromatic sensor arc 
provided for both unsharpened and sharpened image products.