This book provides an overview of the whole radar target recognition process, and covers the key techniques being developed for operational systems. The book is based on the fundamental scientific principles of high resolution radar, and explains how the techniques can be used in real systems.
Inspec keywords: object detection; target tracking; radar tracking; radar target recognition
Other keywords: radar target recognition; high resolution radar; operational systems; target tracking; target detection; real systems
Subjects: Radar equipment, systems and applications; Signal detection; Optical, image and video signal processing; Computer vision and image processing techniques
In the chapter, the radar technology employed for providing high resolution target signatures for recognition purposes is presented. Of particular importance are the practical implementation issues for incorporating the techniques into real systems. Although some mathematics has inevitably had to be used to explain the concepts presented, emphasis has been placed on providing the reader with their physical interpretation. Both the technological and operational aspects of integrating NCTR modes are discussed.
The main objective of this chapter is to provide the reader who is not a radar specialist, with a tutorial on the main aspects of radar design architectures and techniques, which support conventional radar modes. It is aimed to provide the reader with a general understanding of how current radars are designed and how they function by presenting some typical designs, without covering all the detailed techniques available. Radars which employ mechanically scanning antennas such as parabolic reflectors and phased array radars which utilise electronic scanning techniques are presented. The main functional components employed and the basic principles of radar signal processing are also discussed.
In this chapter high-range resolution radar is presented. A high-resolution range profile (HRRP) is a one-dimensional signature of an object. It is a representation of the time domain response of the target to a high-range resolution radar pulse.
In this chapter, techniques for providing high cross-range resolution are presented, which correspond to the direction perpendicular to the radar's radial vector.
The radar and signal processing techniques required to extract the features associated with the propulsion systems tend to use low-range resolution waveforms and utilise time and frequency domain analysis methods. Fairly simple models are presented, which are representative of the techniques used for modelling the effects and performing the target recognition functions. References are provided for readers wishing to study papers following more complex approaches.
The high-resolution techniques presented in this chapter can be considered to be extensions of the main target recognition methods discussed earlier in the book. The super resolution and monopulse techniques effectively improve the resolution of radar measurements by utilising relatively high signal-to-noise ratios. However, for the practical implementation of these methods, the radar must operate at higher than normal sensitivities, which means that the target range is short or there is time available for long integration periods. The polarisation techniques are directly compatible with, and would be used in conjunction with, other high-resolution methods. Relatively high signal-to-noise ratios are required to extract all the polarisation matrix components. The impulse and ultra-wideband techniques are extensions of high-range resolution methods and tend to have niche applications. The combined high-range resolution and high-frequency resolution techniques are based on the respective individual techniques and can be applied to targets with mechanical propulsion systems. Components such as rotors, rotor blades and jet engines can be detected, recognised and localise in range, to supplement range profile data.
This chapter tackles the design issues associated with sensitivity, dynamic range and calibration, which are generally common to most target recognition function. Other key issues such as modification of radar range equation and distortion compensation was also discussed.
The detailed requirements for the radar components needed to support target recognition functions are dependent upon several factors. The key ones are the type of high-resolution mode being employed, the range and the type of target, the level and the reliability of the target recognition capability required and the clutter environment. Although requirements for individual applications vary considerably from recognising ships with ISAR at short range, to discriminating the warhead at a range of several hundred or even thousands of kilometres in ballistic missile defence, general guidelines can be provided.
In this chapter the design issues for supporting high-range resolution modes, using two important classes of antenna, the traditional parabolic dish and the more modern phased array radars, are presented. The topics raised are representative of most types of antenna employed in target recognition. There are no critical issues for JEM associated with the antenna, as it is a narrow bandwidth mode.
From the operational viewpoint tracking radars are considered to be well suited for incorporating high-performance target recognition modes, while maintaining the main tracking function. Active-phased array radars can also support high-resolution modes, but are more constrained by design architecture issues than the trackers. Active arrays with fixed faces have more time available than the rotating designs, so can support modes with longer dwell periods. The passive-phased array radars are the most difficult for incorporating a target recognition function, while maintaining the key operating functions of the radar. However, passive array designs, which include an azimuthal squint capability, provide potential for increasing the dwell period for implementing stepped frequency high-range resolution modes. Phased array radars have surveillance and tracking functions to perform, so target recognition modes have to be implemented within already tight resourcing budgets. For environments with large numbers of targets to be recognised, radars are under development that are to be specifically used for target recognition. For systems, such as tracker radars, that can operate with very short engagement timelines, the target identity decisions would be made automatically. For longer range surveillance and multi-function radars, there would normally be sufficient time for the operator to study the signature data and the computer's recommendations and make the final decision on the target's identity and the appropriate response to the threat.
Within this chapter the main radar recognition techniques for various types of targets have been discussed. In each case, if the radar has the scheduling time available and the hardware is installed, polarisation measurements can also be made. This is particularly true for the high-range resolution measurements. The target recognition techniques are summarised in Tables 11.1-11.4 for the different classes of target for radars installed on ground, naval and airborne platforms.
Within this chapter the various processes which are required to provide a radar target recognition function are brought together and build on the concepts that have been discussed earlier in the book. Key radar measurements issues, which were extensively presented earlier, are reviewed and include a discussion on target signature distortion in Section 12.2.
The measurement of radar signatures has been extensively discussed in this book so far. Although radar is a very powerful technique for providing high-quality signature data for recognising the target, and is generally more reliable than any other technique for beyond visual range identification, other available information can enhance the performance of the recognition function. This chapter discusses other available data and information, which can support and improve radar target recognition, and methods for combining it with radar signature data for maximising performance.
Radar is the key sensor for providing a long-range, all weather, day and night, non-cooperative target recognition capability. In this final chapter, the main radar techniques employed for recognising targets and the key technical and implementation issues are summarised.
The appendices present the classical stepped frequency technique in radar target recognition, the derivation of JEM spectrum and Bayes' theorem.