The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
horizontal and diagonal) and the threshed value is 
computed as follows: 
Original Image 
Non-shadow 
areas 
T univ = a^2log(n) Where a„ is the estimate of the 
standard deviation of additive white noise and n is the 
total number of the wavelet coefficients in a given 
detail image. 
2. 
An image denoising algorithm is applied to attenuate 
the image noise content. A soft thresholding 
(universal technique) (Donoho,1995) is applied to the 
image detail coefficients at each level. This step is 
applied to attenuate the image noise content before 
magnifying image details resulting in a reduced noise 
levels in output details coefficients 
1 de 
3. The original image coefficients are modified by 
adding a percentage of the noise-attenuated 
coefficient values to produce new coefficient values 
dj . The percentage used depends on the image 
entropy in the shadow areas , in addition to the 
entropy of the rest of the image, excluding cloud 
areas. The new coefficient values at each level are 
computed using: 
dj = adj + dj 
(10) 
Where CC = 
image 
' shadow 
Enhanced 
Image 
Figure 1. Schematic diagram of developed algorithm 
4. The image is finally reconstructed using the original 
approximation and modified details C j and dj at 
each level. 3.1 Data 
3. EXPERIMENT 
5. In the spatial domain, a final image is produced that 
has original image values in the non-shadow areas 
and the modified image resulting from step 4 in the 
shadow areas. Shadow edges are then smoothed using 
a Gaussian operator. 
The developed algorithm was implemented on the panchromatic 
band of a November 2001 Landsat 7 ETM satellite subscenes, 
shown in Figure 2. This area represents part of a city suburb 
located close to an airport close to Cairo, Egypt. Features in this 
image are partially obscured by existing cloud patches and their 
associated shadows. It should be mentioned that for simplicity 
the boundary problems were solved by allowing the application 
to process the original scene outside the boundaries of the test 
subscenes when needed, especially for shadow detection stage. 
Figure 3 shows parts of the study image where a runway and 
road intersection are partially shown in shadow areas.