10 band airborne image
1m resolution
select bands R, G, NIR
EE
CIR (1m) coim MS,
averaging image
| subsampling
fsimulaled saleilile produci LUG
t |panchromatic CIR (4m) ; — MSam
; | Image (1m) image ;
i interpolation
RE iia
interpolated |!
+ Comparison
MSinterp
fusion-sharpened ||| _ PSM 1m
CIR image (1m)
Figure 2: Simulation of the satellite imagery, image fusion,
and comparison with the true 1 m imagery.
4 COMPARISON BETWEEN FUSED IMAGE AND
FULL-RESOLUTION IMAGE
Although the result of the fusion-sharpening appears
surprisingly sharp and very satisfactory to the eye, its
spectral truth remains to be checked quantitatively.
When the real satellite imagery becomes available, data
fusion in order to yield highly resolved color images will
certainly be performed. However, the accuracy of the es-
timated color values will remain unknown, and thus also
the errors which propagate through later image process-
ing steps such as land cover classification, change detec-
tion, NDVI computation, etc.
In contrast, with the airborne / simulated imagery we
are in a position to immediately check the deviation be-
tween the multispectral imagery which is truly sam-
pled with 1 m ground resolution and the one interpolated
from 4m resolution by data fusion with 1m panchro-
matic resolution.
The flow chart in Fig. 2 shows the steps involved in the
simulation of the panchromatic and color infrared im-
ages, the fusion and the comparison.
4.1 Spectral Accuracy of the Fused Image
We compare the reflectance values r; of the spectral
bands i € (NIR,R,G) of the fusion-sharpened PSM;4-
image with the color infrared MS;4-image which is truly
sampled at 1m. In Fig. 4 the correlation between the
MS ım-image and the fused PSM,m-image is shown for
the bands Near Infrared, Red and Green. Each pixel de-
fined by its spatial coordinates has two reflectance val-
ues, one in the original and one in the fused image, so
every point in the scatter plot represents one pixel. If
both images were identical, all the points would be lo-
Figure 3: The cubic spline-interpolated CIR image! and the
final fusion-sharpened CIR image! from panchromatic image
(1m) and interpolated color infrared image (4 m).
288 International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
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