Page 76 - Fundamentals of Radar Signal Processing

processing complexity. Many systems use both techniques in series. Clutter

filtering and Doppler processing are the subjects of Chap. 5.

1.5.4 Imaging
Most people are familiar with the idea of a radar producing “blips” on a screen
to represent targets, and in fact systems designed to detect and track moving
targets may do exactly that. However, radars can also be designed to compute
fine-resolution images of a scene. Figure 1.22 compares the quality routinely

obtainable in SAR imagery in the mid-1990s to that of an aerial photograph of
the same scene; close examination reveals many similarities and many
significant differences in the appearance of the scene at radar and visible
wavelengths. Not surprisingly, the photograph is easier for a human to interpret
and analyze, since the imaging wavelengths (visible light) and phenomenology
are the same as the human visual system. In contrast, the radar image, while
remarkable, is monochromatic, offers less detail, and exhibits a “speckled”

texture, some seemingly unnatural contrast reversals, and some missing features
such as the runway stripes. Given these drawbacks, why is radar imaging of
interest?

FIGURE 1.22 Comparison of optical and SAR images of the Albuquerque
airport. (a) K band (15 GHz) SAR image, 3-m resolution. (b) Aerial
u
photograph. (Images courtesy of Sandia National Laboratories. Used with
permission.)

While radars do not obtain the resolution or image quality of photographic