Nautical Depth Sounding- The Rheocable Survey Method

Since 1984, research and development activities have been undertaken in Belgium comprising in situ measurements and sea trials with TSHD ‘Vlaanderen 18’ in Zeebrugge. Towing tank experiments and sludge test tank experiments have also been performed in the laboratories of the Flanders Hydraulic Research. This work has enabled the authors to conclude that mud on the seabed consists of two different physical states occurring in the same configuration - fluid mud on top of solid (consolidating) mud. Fluid mud is navigable, solid mud is not. The interface between both is characterized by a drastic increase of rheological parameters, in particular, the yield stress. However, for the time being, this phenomenon cannot be fully interpreted scientifically. The Rheocable sounding method is designed to detect the interface between fluid and solid mud. A towed object, when kept in a velocity window, is always positioned at this interface between fluid and solid mud. This method makes it possible to develop a new maintenance dredging strategy - leave/ignore the fluid mud and remove only the solid mud. The dredging of fluid mud is therefore unnecessary – it is navigable (!) – and extremely uneconomical. Solid mud on the other hand is not navigable, is immobile and will absolutely maintain its position on the seabed unless removed by dredging action. Furthermore, the deployment of the Rheocable implies many operational and contractual advantages, including transparency of dredged quantities etc. The Rehocable cable sounding method allows for a considerably improved focus, smaller quantities and easier planning of the maintenance dredging activities, resulting in lower budgets and improved safety for shipping traffic.Desde 1984, se han emprendido en Bélgica actividades relacionadas con la investigación y el desarrollo, comprendiendo medidas in situ y pruebas en el mar con el TSHD ‘Vlaanderen 18’, en Zeebrugge. Se han llevado a cabo también experimentos en canale de pruebas hidrodinámicas y experimentos de canales de prueba para sedimentos en los laboratorios de Investigación Hidráulica de Flandes. Este trabajo ha permitido a los autores concluir que el lodo del fondo marino consta de dos estados físicos diferentes en la misma configuración - el lodo fluido en la parte superior del lodo sólido (que se consolida). El lodo fluido es navegable, el lodo sólido no lo es. La interfaz entre ambos está caracteri-zada por un aumento drástico de los parámetros reológicos, en particular la elasticidad. Sin embargo, por el momento, este fenómeno no puede ser interpretado del todo científica-mente. El sondaje empleando el método de flujo ha sido diseñado para detectar la interfaz entre el lodo fluido y el sólido. Un objeto remolcado, cuando se mantiene en una ventana de velocidad, está siempre posicionado en esta interfaz entre el lodo fluido y el sólido. Este método hace que sea posible desarrollar una nueva estrategia de mantenimiento del dragado - dejar/ignorar el lodo fluido y retirar sólo el lodo sólido. El dragado del lodo fluido es pues innecesario - es navegable (¡!) – y extremadamente costoso. Por otra parte, el lodo sólido no es navegable, es inmóvil y mantendrá absoluta-mente su posición en el fondo marino a menos que sea retirado mediante el dragado. Además, el despliegue del método flujo dependiente implica muchas ventajas operaciona-les y transaccionales, incluyendo la transparencia de las cantidades dragadas etc. El sondaje empleando el método de flujo permite un enfoque considerablemente mejorado, cantidades inferiores y una planificación más sencilla de las actividades de mantenimiento del dragado, dando como resultado presupuestos inferiores y una mejora en la seguridad del tráfico marítimo.Depuis 1984, des activités de recherche et de développement . entreprises en Belgique, qui comprennent des mesures in situ et des essais à la mer sur le TSHD ‘Vlaanderen 18’ à Zeebrugge. Des expériences dans des bassins d’essais de carène et des expériences dans des bassins de boue ont également été réalisées dans les laboratoires de la Flanders Hydraulic Research. Ces travaux ont permis aux auteurs de conclure que la boue du fond marin consiste en deux différentes compositions physiques qui se présentent sous la mê-me configuration – boue fluide sur un sommet de boue solide (en consolidation). La boue fluide est navigable, la boue solide ne l’est pas L’interface entre les deux est caractérisée par un accroissement drastique des paramètres rhéologiques, en particulier le seuil d’écoulement. Toutefois, pour le moment, ce phénomène ne peut pas être entière-ment interprété au niveau scientifique. La méthode Rheocable de sondes est destinée à détecter l’interface entre la boue solide et la boue fluide. Un objet tracté lorsqu’il est maintenu dans une fenêtre de vélocité est tou-jours positionné à l’interface entre la boue fluide et la boue solide. Cette méthode rend pos-sible le développement d’une nouvelle stratégie de dragage d’entretien. – de laisser/ignorer la boue fluide et d’enlever seulement la boue solide. Le dragage de boue fluide n’est donc pas nécessaire – c’est navigable – et extrêmement peu économique. D’un autre côté, la boue solide n’est pas navigable, est immobile et dragage. En outre, le déploiement du Rheocable implique des avantages opérationnels et contractuels incluant la transparence sur les quantités draguées, etc. La méthode de levés Rheocable permet une mise au point considérablement améliorée, de plus petites quantités et une planification plus aisée des activités de dragage d’entretien, ce qui a pour résultat une réduction des budgets et l’amélioration de la sécurité du trafic maritime

COMPARING TWO METHODS TO SOLVE THE LAYERED SPHERE PROBLEM, APPLICATION TO ELECTROMAGNETIC INDUCTION SENSORS.

The layered sphere problem can be solved by using a multipole expansion in each layer and imposing the appropriate boundary conditions. This direct approach has some drawbacks because it can be numerically badly conditioned. We show that a tranmission line (TL) formalism can be used to solve the problem and that this approach is better conditioned than the direct approach. The corresponding TL is inhomogeneous because it has a characteristic impedance which varies with the radius and which also depends on the direction. We show how the classical TL expressions can be generalized to take into account such an inhomogeneous TL. Both formalisms are applied to a configuration representative of a metal detector (MD) above a magnetic soil. For such a configuration, a large number of the terms is required in the expansion and the direct approach fails in computing the high order terms because of numerical saturations. In contrast, accurate results are obtained with the TL approach. Key words: layered sphere, multipoles, transmission line, characteristic impedance, metal detector

Volume of Influence for Magnetic Soils and Electromagnetic Induction Sensors

The concept of volume of influence (VoI) for electromagnetic induction (EMI) sensors is introduced and accurately defined. It enables one to better understand the response of a magnetic soil to an EMI sensor, as well as the effect of soil inhomogeneity on soil compensation. The VoI is first defined as the volume producing a fraction a of the total response of a homogeneous half-space. As this basic definition is not appropriate for sensor heads with intrinsic soil compensation, a generalized definition is then proposed. These definitions still do not yield a unique VoI, and a constraint must be introduced to reach uniqueness. Two constraints are investigated: one yielding the smallest VoI and the other one the layer of influence. Those two specific volumes of influence have a number of practical applications which are discussed. The smallest VoI is illustrated for typical head geometries, and we prove that, apart from differential heads such as the quad head, the shape of the smallest VoI is independent of the head geometry and can be computed from the far-field approximation. In addition, quantitative head characteristics are provided and show-among others-that double-D heads allow for a good soil compensation, assuming, however, approximate homogeneity over a larger volume of soil. The effect of soil inhomogeneity is further discussed, and a worst case VoI is defined for inhomogeneous soils

verification

Applying Bayes based classifiers for decision fusion in a multi-modal identit

Modeling the Response of Electromagnetic Induction Sensors to Inhomogeneous Magnetic Soils With Arbitrary Relief

A general model to compute the response of an electromagnetic induction sensor to a magnetic soil, in both time and frequency domains, is developed. The model requires modest computational resources and can be applied to arbitrary soil inhomogeneities and relief, and to arbitrary sensor coil shapes, orientations, and positions. Central to the model is the concept of a head sensitivity map, which can be used to characterize the sensor head as a function of the shape, size, and position of the sensor coils. Two further concepts related to the head sensitivity are presented, which are the zero equisensitivity surface and the volume of influence. We demonstrate that these concepts aid the understanding of the detector behavior. The general model is based on the Born approximation, which is valid if the soil magnetic susceptibility is sufficiently small. A simpler model, which is only valid for homogeneous half-space soils but does not require the Born approximation, is also developed. The responses predicted by both models are shown to be in good agreement with each other and also with available analytic solutions. Comparing the two models also enabled an expression for the error incurred when using the Born approximation to be established. We shown that, for most soils of relevance to mine clearance, the corresponding error is negligible