slide 42

The speaker explains why it is not possible to use the FAST information in a SAR image. The FAST, or SAR pixel, contains information about the satellite-pixel distance and the sum of scatters in the pixel. However, the scatters and the FAST angle vary between pixels, resulting in a random lag pattern in the SAR image. Therefore, the FAST image does not provide any useful information. Some of you may wonder why we don't use the FAST information in a SAR image. Why do we only can obtain useful information from interference between two SAR images? You can understand the reason when looking at the components in a FAST in a SAR image. For a FAST in a SAR image, or we can say a SAR pixel, it contains the information about the distance between the satellite and the pixel, phi r, and the information about the sum of the scatters in the pixel, phi scatters. Note that the FAST is within 2π. The cost of the phi scatters is similar to the Speckle effect. The final backscatter of the pixel is the sum of the scatters in the pixel. The orientation of the factor is the FAST angle. Because scatters are different in different pixels, phi scatters are different in different pixels. In comparison with Speckle effect, the FAST angle is more sensitive to the amplitude. So phi scatters show random lag pattern in space, which results in a random lag pattern in the FAST of a SAR image. In the left figure, which is the FAST in a SAR image, you cannot see any useful information from it.