Ibrahim Olcer

Adaptive Temporal Matched Filtering for Noise Suppression in Fiber Optic Distributed Acoustic Sensing

Distributed vibration sensing based on phase-sensitive optical time domain reflectometry (ϕ-OTDR) is being widely used in several applications. However, one of the main challenges in coherent detection-based ϕ-OTDR systems is the fading noise, which impacts the detection performance. In addition, typical signal averaging and differentiating techniques are not suitable for detecting high frequency events. This paper presents a new approach for reducing the effect of fading noise in fiber optic distributed acoustic vibration sensing systems without any impact on the frequency response of the detection system. The method is based on temporal adaptive processing of ϕ-OTDR signals. The fundamental theory underlying the algorithm, which is based on signal-to-noise ratio (SNR) maximization, is presented, and the efficacy of our algorithm is demonstrated with laboratory experiments and field tests. With the proposed digital processing technique, the results show that more than 10 dB of SNR values can be achieved without any reduction in the system bandwidth and without using additional optical amplifier stages in the hardware. We believe that our proposed adaptive processing approach can be effectively used to develop fiber optic-based distributed acoustic vibration sensing systems.

RF injection locked 18 GHz regeneratively mode-locked semiconductor laser

In this manuscript, a semiconductor based fiber ring cavity mode-locked laser regeneratively driven at 18 GHz is presented. The optical spectrum of the laser is centered at 1578 nm. The laser is RF injection locked via an external source at 18 GHz. The phase noise of the mode-locked laser is measured and the integrated timing jitter was found to be 10.8 fs (from 100 Hz to 20 MHz) and 13.3 fs (from 100 Hz to Nyquist frequency). The integrated amplitude fluctuation (from 100 Hz to 20 MHz) was less than 0.02%. The laser phase and amplitude noise responses to various injected RF power levels were also investigated. The injection RF power has significant effect on the phase noise and the best jitter value is around 40 dB lower than the cavity regenerated RF power.

Field tests of a distributed acoustic sensing system based on temporal adaptive matched filtering of phase-sensitive OTDR signals

Distributed acoustic sensing (DAS) based on phase-sensitive optical time domain reflectometry (OTDR) is being widely used in several applications and attracting significant research interest. The main challenge in coherent detection-based phase-sensitive OTDR systems is the speckle-like background noise which impacts the detection performance and conventional techniques are not suitable for detecting weak vibrations under strong background noise. Recently, we proposed a temporal adaptive filtering (AMF) technique to reduce the background noise in phase-sensitive OTDR systems. The AMF method is based on linear filtering of the optical backscattered signals and the filter coefficients are computed from the observed data. In this study, after briefly reviewing the fundamental theory underlying the adaptive algorithm, we present the effectiveness and performance results of the AMF technique with the field tests. The impact of the diagonal loading level which is used to solve the ill-conditioning of the estimated noise covariance matrix is investigated. Performance dependence of the AMF technique on filter size and a comparison with the conventional trace averaging is presented. It is demonstrated that with the AMF technique, more than 10 dB of SNR values can be achieved without introducing additional optical amplifier stages in the DAS hardware. It is shown that intruder activities 25 m far away from a buried SMF-28 fiber underground can be detected with the proposed technique efficiently.

A novel data adaptive detection scheme for distributed fiber optic acoustic sensing

We introduce a new approach for distributed fiber optic sensing based on adaptive processing of phase sensitive optical time domain reflectometry (Φ-OTDR) signals. Instead of conventional methods which utilizes frame averaging of detected signal traces, our adaptive algorithm senses a set of noise parameters to enhance the signal-to-noise ratio (SNR) for improved detection performance. This data set is called the secondary data set from which a weight vector for the detection of a signal is computed. The signal presence is sought in the primary data set. This adaptive technique can be used for vibration detection of health monitoring of various civil structures as well as any other dynamic monitoring requirements such as pipeline and perimeter security applications.

Microwave wall interior imaging algorithm

In this study, shape and location of the buried objects in the wall is detected by using 2D microwave imaging method. Ultra wide band microwave imaging is a non-destructive imaging technique to image ground layers, to detect mine, explosive and objects behind or in the obstacle. Microwave imaging aims the reconstruction of the material properties of an object by measuring the scattering of an electromagnetic signal it is illuminated with. The hidden objects, which have different kind of material properties, are imaged by using suggested non-destructive microwave imaging algorithm.

An SCA complaint software defined radio application

In this paper, an SCA based HF waveform implementation on an own developed single board computer hardware (GÖMSİS) is presented. The JTRS program in the United States is developing the SCA Standard which defines the specifications for new generation software defined radios. The software defined radios are expected to gain great flexibility and reconfigurability by the help of this standard. In this study, an SCA based HF modem application has been developed and ported to our own platform. The lessons learned from the design and implementation of an SCA based waveform are presented. NATO STANAG 4285 HF modem is selected to be the target waveform in this work.

Implementation of polyphase-FFT based channelizer on FPGA

In this paper a channelizer implementation is performed on FPGA by first a demonstration through simulation and then by applying real test signals. In this study, polyphase FFT based method is selected as the channelization method. The wideband signal, with the bandwidth of 50 MHz, is sampled by 105 MHz and divided into 64 channels with the channel spacing of 0.82 MHz while each one has a sampling frequency of 1.64 MHz and complex outputs. The filter that discriminates between channels has a bandwidth of 1 MHz which allows a certain degree of interference between the adjacent channels, enabling the derivation of signals existing at the intersection area of these channels. In order to realize this, two times oversampling is used for each channel. The design is first simulated in MATLAB environment, and then coded in VHDL and simulated in ModelSim environment. After simulations, the design is synthesized in Xilinx-ISE and loaded to the development board with Virtex-4SX35 FPGA on it, for further testing with real signals.