In: Wagner W., Szekely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
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To evaluate the potentiality of the IKONOS pan-sharpened 
images in terms of the landslide study, an inventory of the 
landslide to be considered as “ground truth” was needed. To 
this purpose, a thematic map reporting soil slide phenomena 
occurred on the test area during autumn-winter 2004-2005 has 
been produced by IRPI-CNR with the usual “state of art” 
stereoscopic photointerpretation techniques. 
4. METHODOLOGY 
The IKONOS multispectral images have been aligned with the 
related panchromatic image by a suitable pre-processing. Then 
the multispectral bands have been pan-sharpened with the 
panchromatic image by means of the fusion techniques under 
analysis, that is the GIHS, the PC, the GS, the GSG and the 
GSA-CA. The PC and the GS pan-sharpening have been 
performed by means of the related tools of ENVI, whereas the 
GIHS, the GSG and the GSA-CA fusion techniques have been 
carried out with a devoted software developed by IFAC-CNR. 
The radiometric correction, usually performed before the fusion 
procedure to achieve a conformity with a mean and variance 
equalization of the bands (Gaurguet-Duport et al., 1996, 
Schowengerdt, 1997; Mather, 1999) have not been performed in 
our study because not necessary, since a physical significance 
of the pixel value is not required in the proposed procedure of 
quality evaluation. As a matter of fact, the study is based on a 
qualitative visual inspection and on a quantitative evaluation of 
suitable score indexes: the visual inspection is focused only on 
the analysis of the features of the images, and since no 
threshold with physical given value is applied, it is not a-priori 
necessary to have pixel value with a physical significance. The 
quantitative assessment is made by performing a comparison 
with the original images by considering the Wald’s protocol, 
and can be carried out in terms of the digital number all the 
same. Moreover, the GSG and GSA-CA methods perform an 
injection of details that is weighted by some statistical functions 
of the images, and the generation of the synthetic intensity band 
from the multispectral bands is carried out in order to obtain the 
desired conformity with the original Panchromatic image. In the 
application of the GIHS-based pan-sharpening method, an 
histogram matching is instead necessary. The pan-sharpened 
data are then orthonormalized with the related tools of ENVI by 
considering a DEM at 10m of spatial resolution and the 
Rational Polinomial Coefficient (RPC) provided together with 
the IKONOS data, and finally the quality assessment is 
performed. 
quality measured by some quantitative score indexes proposed 
in literature and the quality in term of landslide detection 
assessed with a visual inspection is therefore an interesting 
question to be analysed. 
5.1 Quantitative evaluation 
The quality assessment has been performed by evaluating the 
synthesis property proposed by Wald (Wald et al. 1997). As 
depicted in Figure 1, the original Panchromatic (Pan) and 
Multispectral (MS) images are spatially reduced by the same 
factor, so that the new spatial resolution of the Pan image is 
equal to the original resolution of the MS images. 
Figure 1. The adopted quality assessment procedure. 
The degraded MS image is then pan-sharpened with the 
degraded Pan image, thus originating a fused MS image at the 
same spatial resolution of the original MS image; in such a way 
the original MS image can be adopted as reference. Trivially, 
the fused image has to be as similar as possible to the reference, 
to fulfill the so-called synthesis property. The synthesis 
properties have been evaluated by means of some quality 
indexes. The definition of quality index suitable for such task is 
still an open question (Li, 2000; Thomas and Wald, 2005), and 
the fidelity comparison is often performed by more than one 
index, each of them defined to take into account different 
characteristic of the image, such as spectral or spatial matching. 
In this work, five score indexes have been considered. The 
overall assessment on the entire data set has been performed by 
considering the ERGAS (relative dimensionless global error in 
synthesis) index, defined as: 
5. QUALITY EVALUATION 
Quality evaluation of the pan-sharpened images can be 
performed, as a general rule, in two ways, that based on 
quantitative assessment, spatial and/or spectral, and that based 
on a qualitative visual inspection. It is important to point out 
that either the quantitative and the qualitative assessment can be 
performed globally or by considering local characteristics of the 
images. This procedure is of particular interest in some given 
task, such as the landslide detection considered in this paper. 
Therefore, the quality ranking produced with a general visual 
inspection could differ from the quality ranking obtained when 
the specific task of landslide detection is considered; similarly, 
the quantitative result obtained with a general-purpose score 
index could be not suitable to assess the quality of the fused 
products for this particular task. The correlation among the 
ERGAS 4 
1 y. /HMSE(k)\ 2 
k \ Kk) ) 
(i) 
where h/1 is the ratio between the pixel size of PAN and MS 
image respectively, K is the number of bands labelled with the k 
index and p(k) is the mean of the k-th band. The fidelity from 
spectral point of view has been assessed by using the Spectral 
Angle Mapper (SAM) index, a point-wise score defined for 
each pixel (i,j) as: