3.3. Performing the mosaic
For each of the sixteen ASTER images, a spectral subset is performed
on a band by band base for each of the nine bands (visible
and visible near infrared). A subset is performed on each
image and the image is rotated based on the rotation angle
of the satellite, and to get the true North direction of the
image. Gram Schmidt sharpening is performed on each of
the SWIR bands (bands from 4 to 9) to change their spatial
resolution from 30 to 15 m. After performing the Gram
Schmidt sharpening, a difference in pixels and rows between
VNIR and SWIR appears so the difference is cut between
them for each band at each image, to obtain the same pixel
and row numbers. Using a buffer zone of 25 km, each band
is cut and subset for the sixteen images using the buffer zone
around the road from both sides (which is believed to be the
area influenced by the road).
A mosaic is obtained for each image with its neighboring
one by adjusting the stretch, feathering and deciding the fix/
adjusted image based on the quality of the images. It is preferred
to be done strip by strip or path by path as they might
have the same acquisition date and same sun angle and other
parameters which make the mosaic simpler. The area was
divided into many strips and the mosaic was executed on them
strip by strip. A full mosaic is made for each band of each
image at that strip (producing new images having the same
band from all of them), then a band base mosaic was created
(example: band 1 for all images, band 2 for all images . . .,
etc.). Fig. 5 shows the gray scale mosaic for the whole study