So far, most of our discussion has concerned RAR, in which the antenna is a physical object that first emits, then collects the radiation. We now turn our attention to the case in which the antenna moves to cover a synthetic aperture (L_SA), thus producing SAR. SAR generally refers to the case of a moving radar and a stationary target - usually an extended scene, such as the surface of the Earth; ISAR refers to the case in which the radar is relatively stationary and a rotating target provides all (or most) of the motion to create the synthetic aperture. Obviously, those distinctions are not fundamental, because they depend on the user's coordinate system. Furthermore, the two concepts are not mathematical inverses, and there are gray areas where they merge. This chapter assumes an LFM SAR waveform. It also assumes that the Earth's surface is stationary and (except as noted) flat. For a discussion of SAR imaging of the ocean, which is moving.

Chapter Contents:

• 7.1 Introduction to SAR
• 7.1.1 SAR Modes
• 7.1.2 Range and Velocity Contours
• 7.1.3 Motion Compensation
• 7.1.4 Slant and Ground Planes
• 7.1.5 Pulse Repetition Frequency Requirements for SAR
• 7.1.6 Range Migration
• 7.2 SAR Waveforms and Processing
• 7.2.1 Fast-Time Processing
• 7.2.2 Slow-Time Processing
• 7.3 SAR Image Quality
• 7.3.1 Impulse Response
• 7.3.2 Signal-to-Noise Ratio
• 7.3.3 Integrated Sidelobe Ratio
• 7.3.4 Multiplicative Noise Ratio
• 7.3.5 Comparison of SAR and Optical Imagery
• 7.4 Summary of Key SAR Parameters
• 7.5 Special SAR Applications
• 7.5.1 Moving Targets
• 7.5.2 Vibrating Targets
• 7.5.3 Measurement of Object Height
• 7.5.4 Forward-Look SAR
• 7.5.5 Foliage-Penetration SAR
• 7.5.6 Polarimetric SAR
• 7.5.7 Interleaved SAR/ISAR Modes
• References
• Problems

Inspec keywords: radar antennas; synthetic aperture radar; geophysical techniques; Earth; FM radar; antenna radiation patterns; radar imaging; radar interferometry

Other keywords: LSA; LFM SAR waveform; Earth surface; antenna radiation collection; SAR imaging; gray area; RAR; user coordinate system; stationary target; synthetic aperture radar; mathematical inverse; ISAR

Subjects: Single antennas; Radar equipment, systems and applications