Instrumentation & Measurement Magazine 23-6 - 28

Fig. 9. (a) 1992 processed SAR image; (b) PSDs extracted from convolution and Kernel algorithm.

Thus, the convolution is a local operation in which a filtering kernel is moving on the image to modify a pixel value
according to the neighbors' intensity.
Fig. 8 shows the proposed comparative algorithm for executing convolution and extracting the kernel. It delivers, as
outputs, a processed image (convolution and kernel), a Power
Spectral Density (PSD) of the original image, and a PSD of the
kernel of the same image. Fig. 9 and Fig. 10 display these results
for 1992 and 1996, respectively. In particular, both figures illustrate changes in SAR images. In 1992 (Fig. 9), kernel PSD has
four side-lobes and a one no lobe; the PSD of the original SAR
displays 3 minima at "6", as the value of ordinates. Instead, in
1996, side-lobes of kernel PSD are smoothed, and minima at
the same ordinate "6" are 6 as number. These differences in

PSD, beyond those we can see in the annexed images, clearly
indicate major reflectance in terms of major coverage of trees
in lieu of bare soil. Bare soil reflects major radiation, and then
less absorption, from the radar while soil covered by leaves of
trees displays another reflectance and a stable trend of kernel
PSD with minor peak due also to uniformity of green coverage.
In fact, if we extract the kernel in terms of gaussian distribution, we notice two different shapes of the gaussian kernel
according to Fig. 11a and Fig. 11b, respectively. Fig. 11a illustrates side-lobes of the magnitude (see also Fig. 9) while Fig.
11b demonstrates smoothed side-lobes going towards a flat
shape as per Fig. 10. That is due to the fact that the gaussian
kernel acts as a smoothing filter where the weights are different according to the position of the pixel in regard to the central

Fig. 10. (a) 1996 processed SAR image; (b) PSDs extracted from convolution and Kernel algorithm.
28	

IEEE Instrumentation & Measurement Magazine	

September 2020



Instrumentation & Measurement Magazine 23-6

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