Radar HRRP Measurement of Ships

High resolution range profile (HRRP) has become an important research direction in the field of radar target recognition. Measuring the one-dimensional HRRPs of targets and analyzing their characteristics have great significance and practical application value to target recognition. This paper has practically measured the HRRPs of ships in the sea surface utilizing the x-band phase-coherent pulse compression radar measurement platform, which lays a solid foundation for further research on ship target recognition.


Introduction
Radar high resolution range characteristics, namely the target's one-dimensional high resolution range profile (HRRP), are the coherent sum of the echoes of the target scatterers in each range unit [1], and represent the projection of the target scattering center's complex echo signal on the radar line of sight (LOS) [2], which can reflect the target's shape and structure information. Because of its easy acquisition and accurate target recognition, it has become an important research direction in the field of radar target recognition [3]. As a key component of future reconnaissance system, strengthening the measurement and analysis of Radar high resolution range characteristics has extremely important military application value in target identification.
In this paper, the x-band phase-coherent pulse compression radar measurement platform was used to measure the high resolution range characteristics of ship targets on the sea surface.
Firstly, the paper introduces the background and significance of the measurement. Secondly, the paper introduces the software and hardware of the measurement platform. Thirdly, the measurement parameters and process are briefly introduced. Finally, the paper presents the high resolution range profiles of the ship targets based on the measured data.

Measurement Platform
The measurement platform adopts the advanced phase-coherent pulse compression system. The platform is composed of hardware and software.

Hardware of the measurement platform.
The hardware is mainly composed of antenna, phase-coherent transceiver system and main control computer (embedded data acquisition module), as shown in Fig.1

Measurement parameters
Tab.1 Measurement parameters

Measurement process
Step 1. Antenna alignment Aim the antenna to the target ship Step 2. System calibration Select the working mode as "Calibration Mode" in the control interface of the platform, and record the calibration signal data for compensating the system broadband error, and for the reference of subsequent pulse compression processing.
Step 3. Echo acquisition Select working mode as "Normal Mode". The echo data of the sea were recorded Step 4. Pulse compression Start pulse compression program in MATLAB, and conduct pulse compression processing. Save the results.
Step 5. Profile extraction Set the base noise level (-15dB) as the extraction threshold, and extract the target part exceeding the threshold in the pulse compression result, that is the HRRP of the ship.

Measurement results
This paper completes the acquisition and processing of echo data with one meter range resolution. The echo data are from one ship with different postures and different ships with the same posture.   [4].In order to make this more objective, the scattering gravity center (SGC) [5] is calculated.

HRRP of one ship with different postures
Denoting the HRRP fragment as Posture3 SGC 0.393 0.469 0.693 The reason of above phenomenon is that targets in optical region can be modeled as a set of discrete scattering points, and when the target posture changes, the relative radial distance between scattering points will change. As a result, all SGCs in a range resolution unit will change, namely HRRP posture sensitivity [6].

Conclusion
In this paper, the meter-level HRRPs of one ship with different postures and that of different ships with same posture are measured using the x-band phase-coherent pulse compression radar measurement platform. The results show that the HRRP of a ship has great relationship with its posture, that is to say, the HRRP of the same ship has a strong posture sensitivity, while the HRRP of different ships with the same posture is obviously different.