Ships detection by maritime radars Architectures and signal processing

Maritime and coastal surveillance is of paramount importance. Radar applications in this field are numerous. The primary role of radar is to detect and localize vessels. Classification assistance, based on the radar signature, is often available to facilitate the operator's task.

The article covers the following subjects:

• the contribution of radar to maritime surveillance compared to other sensors;

• different applications for these radars, with their main installation constraints on land, sea or air;

• presentation of architecture choices and key parameters;

• principles and constraints leading to the choice of operating frequency: regulations, size constraints, angular discrimination objectives, atmospheric losses and losses due to precipitation;

• various transmission technologies: TWTAs (Travelling Wave Tube Amplifiers) and solid-state transmitters centralized or distributed on an active antenna;

• antenna scanning technologies: mechanically scanned antennas and active electronically scanned antennas;

• characterization of the transmitted signal in terms of waveform, carrier frequency and polarization ;

• expression of transmitted and received signals in mathematical form;

• main characteristics of the signals involved in the detection process: those of targets, thermal noise and the specific spectral and statistical properties of sea clutter;

• principle of detection chains used in maritime surveillance:

• pulse compression: comparison of the main compression codes and methods, particularly from the point of view of compression sidelobes, which must be kept low when close to the coast or in the event of strong radar echoes;

• non-coherent integration and detection threshold calculation;

• “Track-Before-Detect” post-processing;

• finally, an overview of future trends in maritime surveillance radar.

In the following, we assume that the reader is familiar with the concepts of radar theory, and refer to specialized literature where necessary. These general elements are:

• transmit-receive power budget also known as “radar equation”