Introduction to multi-dimensional radar imaging

Synthetic aperture radar (SAR) and inverse SAR (ISAR) imagery are typically used for monitoring areas of varying sizes for target recognition/identification. Nevertheless, limited resolution, self-occlusion effects, geometrical limitations and difficulties in the image interpretation strongly affect the imaging system effectiveness and hence the performance of automatic target recognition (ATR) systems. Some of these limitations are due to the use of classical monostatic systems that are single channel, single frequency and single polarisation, as they are simpler to build than more complex systems. Nevertheless, solutions have been proposed in the recent NATO SET-196 research task group (RTG) [1] that show the benefit of using multi-channel/multi-static radar imaging systems that can be developed without enormous costs.

The NATO SET-250 RTG on multi-dimensional radar imaging initiated its activities in March 2017 and concluded them in October 2021. The goal of the RTG was to further develop systems and algorithms by extending the system dimensionality to include multi-frequency, multi-polarisation and multi-pass radar. Increasing the performance of radar imaging systems will directly improve the effectiveness of ATR systems. Also, in view of the increasing number of drone-like platforms, multi-dimensional radar will be assessed and compared against mono-dimensional radars in terms of their ability to provide valid support for the classification and recognition of such targets. One of the major efforts that have been made within the RTG was the organisation and execution of the Spadeadam Trials, which have seen the employment of four different airborne radar systems. A range of unique results were obtained and are summarised in the different chapters of this book. It is expected that the large and diverse amount of data collected will be used in future NATO activities with additional results.

The background and motivation of the book is given in Section 1.1, while further detail about multi-channel, multi-static and polarimetric radar is covered in Section 1.2. Section 1.3 then defines metrics for assessing radar imaging performance. Finally, an overview of each chapter in the book is then given in Section 1.4.