Synthetic aperture radar (SAR) provides a particularly convenient way of observing the ocean. Indeed, spaceborne SAR sensors were used from their early years to estimate physical parameters (e.g., currents and winds) and to detect the presence of ships (which usually appear as bright spots over the sea dark background) with allweather day-and-night capabilities. In view of all these applications, it is important to obtain data with the highest possible radiometric accuracy. In this context, special attention must be paid to SAR ambiguity problems. Due to the potential appearance of displaced and attenuated replicas of strong signals ("ghosts") related to bright structures present on the coast or to ships over the sea surface, this issue is especially significant for ship-detection applications, since it may dictate a relevant increase in the number of false detected targets.

Chapter Contents:

• 5.1 Introduction
• 5.2 Azimuth ambiguity modeling
• 5.3 Azimuth ambiguity mitigation in single channel SAR images
• 5.3.1 Point-like targets
• 5.3.2 Distributed targets
• 5.4 Azimuth ambiguity mitigation in polarimetric SAR images
• 5.4.1 Method based on polarimetric analysis
• 5.4.2 Methods based on relation between channels
• 5.5 Summary
• Acknowledgments
• References

Inspec keywords: synthetic aperture radar; radar receivers; radar detection; spaceborne radar; object detection

Other keywords: spaceborne SAR sensors; radiometric accuracy; SAR ambiguity problems; ship-detection application; synthetic aperture radar

Subjects: Signal detection; Radar equipment, systems and applications; Radar theory