Abdalla Osman

Improved target detection and bearing estimation utilizing fast orthogonal search for real-time spectral analysis

The problem of target detection and tracking in the ocean environment has attracted considerable attention due to its importance in military and civilian applications. Sonobuoys are one of the capable passive sonar systems used in underwater target detection. Target detection and bearing estimation are mainly obtained through spectral analysis of received signals. The frequency resolution introduced by current techniques is limited which affects the accuracy of target detection and bearing estimation at a relatively low signal-to-noise ratio (SNR). This research investigates the development of a bearing estimation method using fast orthogonal search (FOS) for enhanced spectral estimation. FOS is employed in this research in order to improve both target detection and bearing estimation in the case of low SNR inputs. The proposed methods were tested using simulated data developed for two different scenarios under different underwater environmental conditions. The results show that the proposed method is capable of enhancing the accuracy for target detection as well as bearing estimation especially in cases of a very low SNR.

Synthetic virtual array processing of GPS sonobuoys for underwater target tracking

This paper explores the coherent processing of an array of GPS sonobuoys as an effective method for enhancing target tracking capabilities and improving the bearing estimation accuracy. The paper mainly focuses on underwater target detection using an array of DIFAR sonobuoys. Currently the bearing estimation of underwater targets using DIFAR sonobuoys field is based on individual element processing. However the low levels of signal to noise ratio (SNR) jeopardize the bearing estimation accuracy. The main factor influence the performance is imposed by the deployment strategy of DIFAR sonobuoys and is related to the inter-element distance between sonobuoys which may exceed the minimum distance requirement for array processing. Other factors are the inter-element distances changes over time as well as sonobuoys initial deployed constellation. In this research, we modified the conventional Bartellet beamforming technique in order to accommodate array processing of a group of GPS sonobuoys. Moreover the paper demonstrates the implication of employing virtual array synthesis method to eliminate the current processing limitations. The proposed methods were tested using simulated data developed for two different scenarios with different underwater environmental conditions. A comparative analysis is presented for Bartellet beamforming application on GPS sonobuoys field using current basic processing techniques versus array processing techniques based on the method proposed in this study. The results show that the proposed method is capable of enhancing the accuracy of target bearing estimation especially in cases of very low SNR. Merits and limitations of the proposed method is discussed and analyzed in this study.

Enhanced GPS narrowband jamming detection using high-resolution spectral estimation

Global positioning system (GPS) technology has enabled accurate positioning and navigation of jamming that deteriorates the positioning accuracy. We focus on accurate detection of GPS jammers in the frequency domain where fast Fourier transform (FFT) is predominantly used. An innovative high-resolution frequency estimation method to accurately detect single and multiple in-band continuous-wave jamming signals transmitted at very close-by frequencies is proposed. The proposed method utilizes orthogonal search that provides robust nonlinear spectral estimation to detect dominant jammer frequencies. The Spirent GSS 6700 GPS simulator was utilized in this study to generate several cases for the GPS L1 signal. The output of the GSS 6700 was acquired using the Novatel FireHose GPS frontend receiver that digitizes and down-converts the signal into in-phase (I) and quadrature (Q) samples. The results demonstrated its capabilities of simultaneously detecting more than one GPS jammer existing at close-by frequencies. It is also shown that jammer frequency estimates obtained for a single jammer are more accurate than those obtained by FFT. Furthermore, FOS yields more accurate results than FFT at considerably smaller window sizes.

Analysis of different GNSS array processing methods utilizing new experimental approach using a Spirent simulator and single frontend receiver

Performing array processing on the Global Navigation Satellite Systems (GNSS) signals in a controlled environment requires costly hardware that most researchers cannot afford. This paper introduces a new experimental approach that substantially reduces that cost. It makes possible the emulation of raw digitized in-phase (I) and quadrature phase (Q) samples of GNSS signals, received by an array of Global Positioning System (GPS) antennas. The proposed technique enables simulating linear, planar and three dimensional (3D) array geometries for any satellite positioning system. In this study, only one Spirent GSS6700 GNSS simulator is used along with a single Novatel Firehose frontend. They are both designed for single antenna systems and are used in this research to simulate a seven element uniform linear array (ULA) and a seven element uniform circular array (UCA). Multiple signal classification (MUSIC), Minimum Variance Distortionless Response (MVDR) and classical beamforming are applied for direction of arrival (DoA) estimation, utilizing both ULA and UCA array structures, in order to verify the proposed experimental approach.

Enhanced underwater target tracking using innovative spectral denoising method

This paper explores the application of an innovative spectral denoisng method to improve underwater target tracking capabilities and the bearing estimation accuracy using uniform linear array of passive sonobuoys. Direction of arrival (DOA) estimation using the denoised array data is attained via Bartlett beamforming which is widely employed in underwater target tracking systems. The proposed technique is tested for simulated single and multiple source detection at relatively low signal to noise ratios. Results are presented to illustrate the improvement in bearing estimation using the proposed technique.

Performance evaluation of a non-linear error model for underwater range computation utilizing GPS sonobuoys

Deployed from an airborne platform or a surface vessel, arrays of GPS sonobuoys can be used to efficiently track and localize submarines. The range of the target of interest can be monitored with the deployed sonobuoys. However, the accuracy deteriorates when the target is on the detection range of only one sonobuoy. The objective of this research is to improve the range computation of the target of interest by establishing a non-linear error model for range error using adaptive neuro-fuzzy inference systems (ANFIS), which has the capabilities of dealing with data of high level of uncertainty and the advantage of being based on neural computation. Furthermore, the performance of the proposed model is examined with both experimental real field data and contact-level simulation data considering different scenarios for both the array of GPS sonobuoys and the target. The results discuss merits and the limitations of the proposed method.

Accuracy enhancement of underwater target detection with time‐frequency analysis techniques

Underwater target detection is mainly based on acoustic emissions generated by the target of interest (TOI) as it propels itself through the ocean, and operates non‐propulsion‐related onboard systems. The spectral signature of these acoustic emissions is used for identification and localization of TOI. This paper focuses on underwater target detection using passive sonobuoys. Discrete Fourier transform (DFT) is used in most sonobuoy processing systems to provide spectral analysis of the received signals. Due to the relatively high noise level and the several sources of interference that may exist underwater, the DFT may not determine the spectral signature of TOI with adequate accuracy. The low signal‐to‐noise ratio (SNR) and the presence of strong interference sources with frequencies close to the TOI frequency jeopardize the detection accuracy, the bearing estimation performance, and target tracking capabilities. The aim of this paper is to: (1) examine the performance of both wavelet packet analysis an...

Impact of underwater noise environment on coherent array processing of global positioning system (GPS) sonobuoy fields

Global positioning system (GPS) sonobuoys are widely used in underwater target localization. Most of the present underwater target tracking utilizing GPS sonobuoys rely on individual processing of the data provided by each sonobuoy. Coherent array processing of GPS sonobuoy fields was recently suggested in order to improve the overall system performance by proper combination of sonobuoys received signal. Therefore, it is essential to study the impact of underwater noise environment on target localization when an array of GPS sonobuoys is utilized. This paper introduces a complete analysis of the effect of different types of noisy environments. The overall system performance is evaluated for each environment for both individual sonobuoy processing and coherent array processing. Simulation was used to examine the effect of both white Gaussian noise and correlated noise on the overall system performance in the presence of two sources of interference at variable signal to noise ratios (SNR). Each sonobuoy sig...