With the increasing climatic extremes, the frequency and severity of urban flood events have intensified worldwide. In this study, image-based automated monitoring of flood formation and analyses of water level fluctuation were proposed as value-added intelligent sensing applications to turn a passive monitoring camera into a visual sensor. Combined with the proposed visual sensing method, traditional hydrological monitoring cameras have the ability to sense and analyze the local situation of flood events. This can solve the current problem that image-based flood monitoring heavily relies on continuous manned monitoring. Conventional sensing networks can only offer one-dimensional physical parameters measured by gauge sensors, whereas visual sensors can acquire dynamic image information of monitored sites and provide disaster prevention agencies with actual field information for decision-making to relieve flood hazards. The visual sensing method established in this study provides spatiotemporal information that can be used for automated remote analysis for monitoring urban floods. This paper focuses on the determination of flood formation based on image-processing techniques. The experimental results suggest that the visual sensing approach may be a reliable way for determining the water fluctuation and measuring its elevation and flood intrusion with respect to real-world coordinates. The performance of the proposed method has been confirmed; it has the capability to monitor and analyze the flood status, and therefore, it can serve as an active flood warning system.

Visual sensing for urban flood monitoring

Regional heavy rainfall is usually caused by the influence of extreme weather conditions. Instant heavy rainfall often results in the flooding of rivers and the neighboring low-lying areas, which is responsible for a large number of casualties and considerable property loss. The existing precipitation forecast systems mostly focus on the analysis and forecast of large-scale areas but do not provide precise instant automatic monitoring and alert feedback for individual river areas and sections. Therefore, in this paper, we propose an easy method to automatically monitor the flood object of a specific area, based on the currently widely used remote cyber surveillance systems and image processing methods, in order to obtain instant flooding and waterlogging event feedback. The intrusion detection mode of these surveillance systems is used in this study, wherein a flood is considered a possible invasion object. Through the detection and verification of flood objects, automatic flood risk-level monitoring of specific individual river segments, as well as the automatic urban inundation detection, has become possible. The proposed method can better meet the practical needs of disaster prevention than the method of large-area forecasting. It also has several other advantages, such as flexibility in location selection, no requirement of a standard water-level ruler, and a relatively large field of view, when compared with the traditional water-level measurements using video screens. The results can offer prompt reference for appropriate disaster warning actions in small areas, making them more accurate and effective.

https://www.mdpi.com/1424-8220/15/2/2369/pdf

Cyber surveillance for flood disasters

An ultrawideband (UWB) radar system for remote ranging based onmicrowave-photonic chaotic signal generation and fiber-optic distribution is proposedand demonstrated experimentally. In this system, an optical-feedback semiconductorlaser with optical injection in the central office generates photonic UWB chaos as probingsignal, and two single-mode fibers transport the optical signal to the remote antennamonitoring terminal and return the corresponding echoed signal back to the centraloffice. In the remote antenna terminal, the photonic signal is transformed into microwavechaos by a fast photodetector and then launched to target by a transmitting antenna,and the echoed signal received by another antenna is converted into optical domain bymodulating a laser diode. The target ranging is achieved at the central office by correlat-ing the echoed signal with the reference signal. We experimentally realize a detectionrange of 8 m, for a free-space target, after 24-km remote distance, and achieve a rang-ing resolution of 3 cm for single target and 8 cm for double targets. In another fiber linkbranch with 15-km fiber transmission, we obtained the 2-cm ranging resolution for asingle target.Index Terms: Chaos, remote radar, semiconductor lasers.

Remote Radar Based on Chaos Generation and Radio Over Fiber

A distributed multiple-input multiple-output chaotic radar based on wavelength-division multiplexing technology (WDM) is proposed and demonstrated. The wideband quasi-orthogonal chaotic signals generated by different optoelectronic oscillators (OEOs) are emitted by separated antennas to gain spatial diversity against the fluctuation of a target’s radar cross section and enhance the detection capability. The received signals collected by the receive antennas and the reference signals from the OEOs are delivered to the central station for joint processing by exploiting WDM technology. The centralized signal processing avoids precise time synchronization of the distributed system and greatly simplifies the remote units, which improves the localization accuracy of the entire system. A proof-of-concept experiment for two-dimensional localization of a metal target is demonstrated. The maximum position error is less than 6.5 cm.

Distributed MIMO chaotic radar based on wavelength-division multiplexing technology.

A wideband complexity-enhanced chaos generation scheme is proposed by using a semiconductor laser subject to delay-interfered self-phase-modulated optical feedback. The influences of feedback strength, phase modulation index, and interference delay on the effective bandwidth and time-delay-signature (TDS) characteristics of the proposed scheme-generated chaos are extensively investigated both experimentally and numerically. The results demonstrate that with the joint effects of phase modulation-induced spectrum expansion and nonlinear filtering of delayed interference, wideband chaos with flat spectrum and excellent TDS suppression characteristics can be generated over a wide dynamic operation range. In comparisons with the relevant chaos generation schemes under conventional optical feedback, individual self-phase modulated optical feedback, and delay-interfered optical feedback, the proposed scheme cannot only significantly enhance the effective bandwidth of chaos but also considerably enhance the complexity of chaos by suppressing the TDS toward an indistinguishable level close to 0.

/pdf/wideband-complex-enhanced-chaos-generation-using-a-5askj8oh9z.pdf

Wideband complex-enhanced chaos generation using a semiconductor laser subject to delay-interfered self-phase-modulated feedback.

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.

Microwave-Photonic Sensor for Remote Water-Level Monitoring Based on Chaotic Laser

We propose and demonstrate a novel scheme to generate time-delay-signature-suppressed broadband chaotic light by using an optically injected laser diode subjected to scattering light feedback. The achievement of broadband chaos is based on the interaction between the injection light and chaotic light from the scattering feedback semiconductor laser via beating. A single-mode fiber as a continuous scatterer is specially used as a feedback cavity to introduce random feedback, which could truly eliminate the time delay signature of chaotic light. The chaotic light with a power spectrum that extends to 13.6 GHz within 3 dB is experimentally achieved.

Time-delay-signature-suppressed broadband chaos generated by scattering feedback and optical injection.

A simple photonic approach to generate ultrawideband (UWB) pulse signals utilizing a gain-switched semiconductor laser with optical feedback is proposed and demonstrated. The RF spectrum of the generated chaotic UWB signals has a -10 dB bandwidth of 9 GHz and central frequency of 6.6 GHz (fractional bandwidth of 155%), which is consistent with the Federal Communications Commission indoor mask. The central frequency and -10 dB bandwidth can be tuned by adjusting the bias current and feedback strength of the semiconductor laser. After transmission through a 30 km single-mode fiber, the spectrum shape of the chaotic UWB signals is almost unaffected by the chromatic dispersion of the fiber.

Photonic generation of ultrawideband signals based on a gain-switched semiconductor laser with optical feedback

A UWB microwave-photonic chaotic radar system for remote ranging is proposed and demonstrated. The chaotic detection signal is transmitted by an ultra-wideband transmitting antenna after a 24 km single-mode fiber transmission to a remote antenna unit. The received signal is converted into the corresponding optical signal through directly modulating and carried by another approximately 24 km single mode fiber back to the central station. The target detection and ranging are accomplished through cross correlation at the central station. Chaotic signals with bandwidths more than 18 GHz are generated experimentally. Ranging of single-target and double-target is demonstrated. The system can not only implement the remote control of the radar, but also has a high range resolution.

http://www.tyut.edu.cn/wuli/institute/2013/jiyongning.pdf

Yongning Ji

Papers

Remote Radar Based on Chaos Generation and Radio Over Fiber

Microwave-Photonic Sensor for Remote Water-Level Monitoring Based on Chaotic Laser

Time-delay-signature-suppressed broadband chaos generated by scattering feedback and optical injection.

Photonic generation of ultrawideband signals based on a gain-switched semiconductor laser with optical feedback

Ultra-wideband microwave-photonic chaotic radar for remote ranging