**Preface to "Innovative Target Tracking Techniques for Modern Radar and Sonar Systems"**

Due to rapid advances in wireless communication and sensor technology, modern monitor systems, including modern radar and sonar systems, play important roles in both civil and defence applications. An important example is target tracking. Nowadays, radar and sonar systems constantly encounter a large number of targets of many different types, such as extended targets and low signal-to-noise ratio targets. These types of targets bring new challenges to target-tracking techniques. To cope with these challenges, conventional target tracking methods need to be significantly upgraded. There are several theoretical and practical problems, such as multi-sensor fusion architecture, track-before-detect methods, classification and identification methods, and other open problems yet to be addressed. The corresponding applications of machine learning in this field are also interesting and meaningful topics of investigation.

The aim of this Special Issue is to gather recent advances and development in target tracking techniques to determine how they can be adapted for modern radar and sonar systems. After peer review, 17 articles in related areas have been accepted for publishing in this Special Issue. The published articles cover a range of topics and applications central to target tracking, such as extended target tracking, resource management, and multi-target smoother. Although this Special Issue has been closed, the need for future research and development related to innovative target-tracking techniques for modern radar and sonar systems remains. We hope that this Special Issue and the published papers can inspire many more innovative theoretical and practical efforts in the field of target tracking.

> **Alfonso Farina, Wei Yi** *Editors*
