Yuta Izumi

Development of circularly polarized synthetic aperture radar on-board UAV JX-1

ABSTRACT We developed L band (frequency 1.275 GHz) circularly polarized synthetic aperture radar (circularly polarized SAR) on-board unmanned aerial vehicle (UAV). This paper explains the configuration of system, antenna, and car-based experiment of circularly polarized SAR. The comparison of circularly polarized SAR and linearly polarized SAR by full polarimetric scattering experiment in anechoic chamber was done and discussed. The result shows circular polarization has less effect of orientation angle of target and could avoid the misalignment of transmitter and receiver antenna during UAV operation. Axial ratio and ellipticity images are also derived and introduced as novel classification technique in microwave remote sensing field using circularly polarized SAR or ellipticity characteristic of scattering wave.

The Development and Comparison of Two Polarimetric Calibration Techniques for Ground-Based Circularly Polarized Radar System

Two techniques are described for the calibration of ground-based (GB) circularly polarized (CP) full polarimetric radars. The techniques are based on the point target calibration approach that uses various types of canonical reflectors with different orientations. Specifically, the calibration methods for linearly polarized (LP) radar proposed by Wiesbeck et al. and Gau et al. are selected and adapted to CP with suitable reflectors. The applicability of the techniques is examined through C-band scatterometric and synthetic aperture radar (SAR) measurements in an anechoic chamber. For the scatterometric mode, comparisons of calibrated channel imbalances with theoretical values show agreement within ±0.3 dB in amplitude and ±5◦ in phase. The crosstalk between the channels is also reduced by ∼ 5 to 30 dB after calibration. For the SAR mode, calibrated scattering matrix of a vertical wire target exhibits significant elimination of distortions between channel amplitudes and phases. The effect of calibration on target parameter retrieval is also investigated through the Cloud-Pottier eigenvector-based decomposition. Both calibration techniques are shown to yield improved accuracy of entropy-alpha (H-ᾱ) distributions and orientation angle (β̄) values.

Novel chirp phase error compensation algorithm using polynomial chirp modeling for high resolution synthetic aperture radar

This paper proposes the phase error compensation algorithm of the wide band chirp generator for the synthetic aperture radar (SAR) use. The proposed algorithm dynamically calculates the phase error of transmitting chirp to reduce spurious of signal. In addition, it uses the curve fitting method and feedback when the desired signal are set by user. Numerical results show that the proposed algorithm can enhance the impulse response function (IRF) results such as the peak to side-lobe ratio (PSLR) and the integrated side-lobe ratio (ISLR) up to −0.1561 dB and −0.0548 dB respectively. Furthermore, the spurious has been reduced by compared to the conventional direct digital frequency synthesizer (DDFS) chirp generators.

Analysis of Circular Polarization Backscattering and Target Decomposition Using GB-SAR

Currently, most full-polarimetric synthetic aperture radar (SAR) systems adopt linear polarization (LP). On the other hand, circular polarization (CP) is also becoming popular due to its various benefits over LP. However, since CP-SAR is an emerging technique, there are not many imaging and polarimetric analysis results in the literature. As a fundamental study on CP-SAR, this paper presents the results of an investigation on the CP properties of ground-based SAR (GB-SAR) echoes from various canonical targets and a rice paddy sample. The C-band data acquired in a laboratory environment are analyzed and interpreted by means of several factors such as calibration performance, experimental verification of theoretical scattering matrices, imaging quality and accuracy of scattering decomposition results. The eigenvector-based decomposition of the coherency matrix is adopted, and the performance of CP in retrieving the targets’ dominant scattering mechanisms and physical parameters is evaluated from entropy-alpha (H -ᾱ) plane and orientation angle (β̄) value. Results demonstrate the effectiveness of CP in interpreting and discriminating the SAR image features mainly owing to its distinct advantage of highly reliable received signal strength.

The polarimetric calibration method for ground-based circularly polarized synthetic aperture radar

A polarimetric calibration method for circularly polarized (CP) synthetic aperture radar (CP-SAR), where both transmitting and receiving antennas are CP, is proposed in this paper. The proposed CP polarimetric calibration method is based on a conventional polarimetric calibration method proposed by Wiesbeck et al. where only canonical targets are used. Experimental results applied with the proposed calibration method show improvement over uncalibrated measurements in radar cross-section (RCS), amplitude ratio and phase difference of between channel.