The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
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of them in interpolated image is not clear. This problem is 
Figure 12: Problem in the interpolated image (up-left), Cloud 
image (up-right), Original optical image (down-left) and radar 
image (down-right) 
This object was checked in radar image but that cannot be 
separated by radar image from around object. This problem 
may be because of radar image (reflectance is the same with 
around objects) or change of object (radar image and optical 
image are different 6 days). This checking is illustrated in the 
figure 12. 
These objects were estimated by local farmers. That is one type 
of vegetable. Height of this vegetable is about 20-30cm. So, 
reflectance in radar image may be from ground, not from 
vegetable. Cause of radar image (can not separate this object by 
radar image) is higher probability than cause of change of 
object. So, interpolation of under cloud data based on radar 
image will be not so good at some special objects. However, by 
using combination of threshold level (a value) for radar image 
and searching the nearest pixel to interpolate cloud pixel, the 
result will have more information than using threshold of whole 
radar image and cloud optical image independently. 
4.2 Cloud Removal of ASTER Image Based on Landsat 
ETM Image 
This method also can apply for combination of two optical 
images to remove cloud if the change of objects is not so much. 
By the same way, cloud was gotten from another image to 
overlay on ASTER image date 2001/11/16. NDVI of Landsat- 
ETM image date 2000/11/04 was used instead of radar image. 
shown in the figure 12. 
Interpolated image is compared with original image by visually. 
Result is very good. Almost there are no change between 
interpolated result and original ASTER image. Result is shown 
in the following figure: 
Figure 13: Original image (left), Cloud image (centre) and 
Interpolated image (right) of ASTER image date 2001/11/16 
By this way, many types of different optical image can combine 
together to remove cloud. We can make a series of free cloud 
multi-temporal data from many types of satellite data for 
studies about monitoring the change of environment and natural 
resource. 
4.3 Combination of Landsat-ETM Image and Landsat- 
ETM Image 
Here is another application of this method. Two Landsat-ETM 
images date 2002/01/05 and 2001/02/03 were used. Both of 
them have cloud. These two images can be combined together 
to make two free cloud images. In this case, wavelength of two 
images is the same together. So, interpolation is done based on 
band by band. That means using band 1 to interpolate for band 
1, band 2 to interpolate for band 2, band 3 to interpolated for 
band 3 and so on. The first, cloud part in the image date 
2001/02/03 was removed based on the image date 2002/01/05. 
Result is shown in the following figure: 
Figure 14: Cloud image (left) and resuit image (right) of 
Landsat-ETM image date 2001/02/03 
By the same way, cloud part in the image date 2002/01/05 was 
removed based on the image date 2001/02/03. Result is shown 
in the following figure: