THE HIGH FREQUENCY SURFACE WAVE RADAR SOLUTION FOR VESSEL TRACKING BEYOND THE HORIZON

With maximum range of about 200 nautical miles (approx. 370 km) High Frequency Surface Wave Radars (HFSWR) provide unique capability for vessel detection far beyond the horizon without utilization of any moving platforms. Such uniqueness requires design principles unlike those usually used in microwave radar. In this paper the key concepts of HFSWR based on Frequency Modulated Continuous (FMCW) principles are presented. The paper further describes operating principles with focus on signal processing techniques used to extract desired data. The signal processing describes range and Doppler processing but focus is given to the Digital Beamforming (DBF) and Constant False Alarm Rate (CFAR) models. In order to better present the design process, data obtained from the HFSWR sites operating in the Gulf of Guinea are used.  

Polarimetric Incoherent Target Decomposition by Means of Independent Component Analysis

International audienceThis paper presents an alternative approach for polarimetric incoherent target decomposition dedicated to the analysis of very-high resolution POLSAR images. Given the non-Gaussian nature of the heterogeneous POLSAR clutter due to the increase of spatial resolution, the conventional methods based on the eigenvector target decomposition can ensure uncorrelation of the derived backscattering components at most. By introducing the Independent Component Analysis (ICA) in lieu of the eigenvector decomposition, our method is rather deriving statistically independent components. The adopted algorithm - FastICA, uses the non-Gaussianity of the components as the criterion for their independence. Considering the eigenvector decomposition as being analogues to the Principal Component Analysis (PCA), we propose the generalization of the ICTD methods to the level of the Blind Source Separation (BSS) techniques (comprising both PCA and ICA). The proposed method preserves the invariance properties of the conventional ones, appearing to be robust both with respect to the rotation around the line of sight and to the change of the polarization basis. The efficiency of the method is demonstrated comparatively, using POLSAR Ramses X-band and ALOS L-band data sets. The main differences with respect to the conventional methods are mostly found in the behaviour of the second most dominant component, which is not necessarily orthogonal to the first one. The potential of retrieving non-orthogonal mechanisms is moreover demonstrated using synthetic data. On expense of a negligible entropy increase, the proposed method is capable of retrieving the edge diffraction of an elementary trihedral by recognizing dipole as the second component

Tracheotomy in children

IntroductionTracheotomy is one of the most urgent procedures in medicine. It is an operative procedure that creates a surgical airway in the cervical trachea.AimTracheostomy refers to a surgical incision made into a trachea. Children are often considered “little people”, however, in medical sense, that is not completely true. The aim of our paper is to review the tracheostomy procedure in children.Materials and MethodsIn this paper, we analysed the tracheostomies in children performed in the Clinical Centre Niš (Serbia) in the five-year period from January 2015 to December 2019 inclusive. At our centre, all tracheostomies were solely performed by otolaryngologists.ResultsA total of 37 tracheotomies were performed in the studied period. There were 25 (67.6%) boys and 12 girls (32.4%). The main reason for this relatively low tracheostomy count in our study is because our practitioners are usually performing tracheostomies only in children that require urgent care. All chronic or complicated cases, if they are stable enough to transport, are referred to a higher specialised institution in Belgrade, Serbia.The youngest was a newborn, not older than 1 hour, and the oldest was 17 years old. We divided them into groups according to the age. There were 5 (13.5%) neonates, 25 (67.6%) infants, 3 (8.1%) preschoolers, 2 (5.4%) school-aged children, and 2 (5.4%) adolescents. This is in concurrence with other studies, where authors reported that the highest number of tracheostomies (around 65–70%) were performed before 1 year of age.In most cases, indication for tracheostomies were upper airway obstructions (n = 35, 94.6%). Prolonged orotracheal intubation (n = 1, 2.7%), and protective tracheostomy (n = 1, 2.7%) were the causes in the other two cases.ConclusionWhile researching the literature for this paper we found that there is little standardisation associated with tracheostomy, even though it is a procedure that is performed regularly all over the globe. There is evidence that there is a disparity in opinions not only among the practitioners in different countries, but in individual countries as well. With the increasing number of patients that require tracheostomy, we find that this topic should be addressed more carefully with the attempt to establish the best way of action for this procedure, and with that, lower the complication and mortality rates

Poincare Sphere Representation Of Independent Scattering Sources: Application On Distributed Targets

International audienceThis paper introduces Independent Component Analysis (ICA) to the Incoherent Target Decomposition theory (ICDT) through the particular application - snow cover analysis. Given that the equivalence of the currently used eigenvalue decomposition and Principal Component Analysis (PCA) can be stated under certain constraints, the goal is to generalise ICDT in the context of Blind Source Separation (family of techniques comprising both PCA and ICA). This generalisation allows independent non-orthogonal backscattering mechanisms retrieval in case of non-Gaussian polarimetric clutter. The obtained independent target vectors are parametrized using the Target Scattering Vector Model (TSVM). The algorithm is applied on a distributed target - snow cover, and the obtained parameters are illustrated and appropriately interpreted using the Poincare sphere

Independent component analysis within polarimetric incoherent target decomposition

International audienceThis paper represents a part of our efforts to generalize polarimetric incoherent target decomposition to the level of BSS techniques by introducing the ICA method instead of the conventional eigenvector decomposition. We compare, in the frame of polarimetric incoherent target decomposition, several criteria for the estimation of complex independent components. This is done by parametrising the obtained dominant and mutually independent target vectors using the TSVM and representing them on the corresponding Poincare sphere. We demonstrate notably good performances of the proposed method applied on the RAMSES POLSAR X-band image, by precisely identifying the class of trihedral reflectors present in the scene. Logarithm and square root nonlinearities - two of the three proposed criteria for complex IC derivation prove to be very efficient. The best discrimination between the a priori defined classes appears to be achieved with the principal kurtosis criterion. Finally, the algorithm using the former two functions leads to very interesting entropy estimation

Wet snow backscattering sensitivity on density change for SWE estimation

International audienceThis paper deals particularly with the sensitivity of the wet snow backscattering coefficient on density change. The presented backscattering model is based on the approach used in the dry snow analysis, appropriately modified to account for the increased dielectric contrast caused by liquid water presence. It encircles our undertaking of simulating and analysing snow backscattering using fundamental scattering theories (IEM-B, QCA, QCA-CP). The wet snow parameters are chosen according to the area of the particular interest - the French Alps, while the choice of the SAR sensor parameters (frequency, polarization) is primarily conditioned by the initially settled goal - reaching qualitative conclusions concerning wet snow backscattering mechanism. Based on simulation results, we state the dominance of the snow pack surface backscattering component, causing the backscattering to be directly proportional to the volumetric liquid water content. This result is confirmed by the performed in situ measurements. We illustrate as well the decrease of this effect with the increase in operating frequency

Analysis of supplementary information emerging from the ICA based ICTD

International audienceThis paper presents an elaboration of the ICA based ICTD, proposed in [1]. The method is applied on three different datasets and three distinctive aspects of its performances are considered. Firstly, we challenge the initial choice of the ICA algorithm, by testing the suitability of two representative tensorial (fourth-order) and one second-order algorithm. Further, we demonstrate the invariance of the proposed decomposition with respect to both the rotation around the line of sight and the change of polarisation basis. Finally, we analyse the potential of supplementary information contained in the second most dominant component

Zernike ultrasonic tomography for fluid velocity imaging based on pipeline intrusive time-of-flight measurements

International audienceIn this paper, we propose a novel ultrasonic tomography method for pipeline flow field imaging, based on the Zernike polynomial series. Having intrusive multipath time-offlight ultrasonic measurements (difference in flight time and speed of ultrasound) at the input, we provide at the output tomograms of the fluid velocity components (axial, radial, and orthoradial velocity). Principally, by representing these velocities as Zernike polynomial series, we reduce the tomography problem to an ill-posed problem of finding the coefficients of the series, relying on the acquired ultrasonic measurements. Thereupon, this problem is treated by applying and comparing Tikhonov regularization and quadratically constrained l1 minimization. To enhance the comparative analysis, we additionally introduce sparsity, by employing SVD-based filtering in selecting Zernike polynomials which are to be included in the series. The first approach - Tikhonov regularisation without filtering, is used because it is the most suitable method. The performances are quantitatively tested by considering a residual norm and by estimating the flow using the axial velocity tomogram. Finally, the obtained results show the relative residual norm and the error in flow estimation, respectively, ~0.3% and ~1.6% for the less turbulent flow and ~0.5% and ~1.8% for the turbulent flow. Additionally, a qualitative validation is performed by proximate matching of the derived tomograms with a flow physical model