A microwave-photonic sensor for remote water-level monitoring based on chaotic laser is proposed and demonstrated. The probe chaotic signal with bandwidth of 18 GHz is generated in the central office and then transmitted at the remote antenna unit after a 24 km single-mode fiber transmission. And the monitoring data from the remote antenna unit is sent back to the central office over fiber. The water-level measuring is accomplished by cross-correlation between reference signal and probe signal at the central office. So the remote water-level monitoring system with a high spatial resolution of 2 cm is achieved and the height of water surface can be displayed in real time.
Chaos through-wall imaging radar has attracted wide attention due to its inherent low probability of detection/interception, strong anti-jamming, and high resolution. However, the target response is usually overwhelmed by strong clutter. This paper proposes an imaging-then-decomposition method based on two-stage robust principal component analysis (RPCA) to remove the clutter and recover the target image. The proposed method firstly focuses the energy of the preprocessing data by the back-projection imaging algorithm; then, it performs matrix decomposition on the full and the sparse component of the focused data, in succession, by the RPCA algorithm. Simulation and experimental results show that the proposed method can suppress the clutter dramatically and indicate human targets distinctly. Compared with the traditional methods, it has effectiveness and superiority in improving the signal-to-clutter ratio.
We experimentally demonstrate radar remote imaging using a radio technique based on ultra-wideband chaotic signals over fiber links. The radar system includes three parts, i.e. a central station, some optical fiber links and a base station. At the central station, an ultra-wideband chaotic signal is generated from an improved Colpitts oscillator and then is up-converted as a probe signal. The probe signal is then converted to be in optical domain by the external modulation technique on laser diode for transmitting over a fiber link to a remote base station. At the base station, the probe signal is converted to be in electrical domain and then launched by a microwave antenna. After being received by another antenna, the echo signal from a target is converted to be in optical domain and then transmitted over a fiber link back to the central station. By optical-to-electrical conversion and down conversion, the echo chaotic signal is recovered. Utilizing the correlation method and back projection algorithm, an image of the target in the two-dimensional space can be realized at the central station. Our experiments successfully performed remote imaging for both planar and spherical reflectors with a distance over 10 km. The down-range resolution of 6-cm and 8-cm cross-range resolution were obtained, respectively. We will show that the power spectrum of the probe signal is adjustable in the spectral mask according to the Federal Communications Commission standards, therefore can avoid interference to the existing narrowband radio signals.
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