The small microwave skin depth of sea water as well as the small penetration depth of laser signal in water impose limitations on the application of SAR and Lidar in sea surveillance systems. On the other hand, vessels travelling at sea bring about hydrodynamic anomalies in the sea water called as wake. These hydrodynamic disturbances can be detected by using some techniques such as airborne radio imaging and Extremely Low Frequency (ELF) electroMAGNETIC signal processing. In practice, the motion of conductive sea water anomalies in the natural earth's MAGNETIC field induces ELF MAGNETIC wakes which can be measured via accurate MAGNETIC sensors and detected through signal processing schemes. The physical properties of the hydrodynamic wake as well as those relating to the corresponding MAGNETIC wake are directly related to the vessel parameters such as hull shape, speed and HEADING. In this work, we firstly derive and formulate the mathematical expressions relating to the aforementioned hydrodynamic and MAGNETIC wakes. By employing derived expressions, a novel detection scheme is proposed based on constructing the 2-dimentional image of the vessel’, s MAGNETIC wake through the MAGNETIC signals captured from an array of MAGNETIC sensors, and finally, the relation between the spectral image of the MAGNETIC wake and the vessel HEADING is studied. We will show that our proposed scheme can detect the existence of a remote vessel as well as its HEADING from the constructed image with high accuracy, and moreover, it does not have common limitations of existing single-sensor based HEADING detection schemes.

This paper is dedicated to design of a low cost and GPS independent navigation system and also implementation of that on a boat. Exact position estimation of a boat is very important and critical in maritime security. There are several different methods for maritime navigation including Doppler navigation, GPS and INS as the three most common methods. With regard to high cost of Doppler navigation due to its expensive sensors, probability of GPS signals lost or distortion and also for cumulative errors in INS and pricey cost in its ultra-accurate types, in this research an open loop estimation method is presented using only HEADING ANGLE and velocity of the vehicle. Due to lack of speed sensor, velocity of the boat is simulated by adding noise to the speed values measured by GPS. Furthermore real data of a magnetometer are used as the boat's HEADING ANGLE measurements. In order to assess the suggested algorithm, two different tests are carried out in Mazandaran Sea and the speed and HEADING ANGLE of the boat are stored during the mission and then off-line implementation of the proposed method is accomplished in MATLAB. Comparing the results with GPS measurements indicates acceptable and desirable performance of the suggested method.

In a strap down MAGNETIC compass, HEADING ANGLE is estimated using the Earth's MAGNETIC field measured by Three-Axis Magnetometers (TAM). However, due to several inevitable errors in the MAGNETIC system, such as sensitivity errors, non-orthogonal and misalignment errors, hard iron and soft iron errors, measurement noises and local MAGNETIC fields, there are large error between the magnetometers' outputs and actual geoMAGNETIC field vector. This is the necessity of MAGNETIC calibration of TAM, especially in navigation application to achieve the true HEADING ANGLE. In this paper, two methodologies, including clustering swinging method and clustering velocity vector method are presented for MAGNETIC compass calibration. Several factors for clustering process have been introduced and analyzed. The algorithms can be applied in both low-cost MEMS magnetometer and high-accuracy MAGNETIC sensors. The proposed calibration algorithms have been evaluated using in-ground and in-flight tests. It can be concluded from the experimental results that, applying the clustering calibration algorithms bring about a considerable enhancement in the accuracy of MAGNETIC HEADING ANGLE.

HEADING estimation is one of the main challenges in low-cost inertial navigation systems (INSs). Non-observability of HEADING ANGLE with gravitational acceleration vector as well as inaccessibility of radio/satellite navigation in underwater vehicles increases the value of this challenge. Applying three-axis magnetometer and HEADING estimation from earth MAGNETIC field components is one of the main approaches to accuracy enhancement of the low-cost inertial navigation systems. However, in order to achieve accurate HEADING estimation, the magnetometer must be appropriately calibrated for both sensor errors and presence of MAGNETIC deviations. This paper aims to develop back-stepping algorithm for magnetometer calibration applied to measure the earth MAGNETIC field components. In the proposed algorithm, the results of the prevalent spherical MAGNETIC calibration are corrected based on vertical channel decomposition and MAGNETIC field components in the horizontal plane. The algorithm is evaluated in the field tests executed on an Autonomous Underwater Vehicle (AUV).

Background and Aims: Disc displacement is the most common temporomandibular joint disorder and MAGNETIC resonance imaging (MRI) is the gold standard in its diagnosis. This disorder can lead to changes in signal intensity of MAGNETIC resonance (MR). The purpose of this study was evaluation of correlation between relative signal intensity of MR images of retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle with type of anterior disk displacement and condylar head flattening in patients with temporomandibular disorder (TMD).Materials and Methods: In this retrospective study, 31 MR images of patients who had anterior disc displacement were evaluated. After relative signal intensity measurement for retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle, the correlation between relative signal intensity and type of anterior disc displacement was evaluated with repeated measure ANOVA test. In each of these 3 areas, t-test was used to compare the groups with and without condylar head flattening.Results: The correlation between relative signal intensity of MR images and type of anterior disc displacement in retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle was not significant. There was also no statistically significant correlation between relative signal intensity of MR images and flattening of condylar head in retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle (P>0.05).Conclusion: According to findings of this study, relative signal intensity of MR images in retrodiscal tissue, superior and inferior head of ptrygoid muscle is not a good predictor for type of anterior disc displacement and flattening of condylar head. It seems that this cannot be used as a diagnostic marker for TMD progression.