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imates were
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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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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Edge Measurement Index
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.