K.Y. Foo

A routing and channel-access approach for an ad hoc underwater acoustic network

In this paper, the concept of an ad hoc underwater acoustic network (UAN) is presented. It seeks to meet two critical needs: to establish a long-range and decentralised communication link, and to maintain a reliable on-demand communication link with minimal human intervention. Despite having the same goal, the operating characteristics of an ad hoc UAN usually differs from its radio counterpart due to the nature of its target applications and the environment in which it operates. The differences must be taken into account in order to achieve an optimal system. Such a scheme is based upon the ad hoc on-demand distance vector (AODV) algorithms developed for wireless radio networks. The considerations necessary for adopting these algorithms are discussed. The multiple-access with collision avoidance and acknowledgement (MACAW) scheme is implemented for the control of medium access. The issues and challenges faced, along with the viability of alternative techniques are discussed. Simulation results are presented.

Robust underwater imaging with fast broadband incoherent synthetic aperture sonar

Synthetic aperture techniques have been of interest to the sonar imaging community, but suffer from the problems of maintaining phase coherence and a slow mapping rate. The need for rigorous and accurate platform trajectory monitoring often increases the design and implementation costs as well as the hardware complexity. The paper examines incoherent processing techniques and shows their potential for use in designing a robust and practical underwater imaging system. A novel, fast, incoherent, time-domain processing technique is presented. The advantages of using incoherent processing for three dimensional imaging are discussed. Broadband signals are used for achieving high range-resolution. Results from simulations and processing of sea-survey data are included.

Standard target calibration of broad-band active sonar systems in a laboratory tank

High-frequency, scientific active sonar systems are frequently calibrated using standard target spheres. Spot frequency calibration accuracies (using carefully optimized sphere diameters) of 0.1 dB have been previously established as theoretically and technically feasible. The premise of this work is that a tungsten-carbide sphere may be used to calibrate an arbitrary sonar system in a laboratory water tank. In order to achieve an accurate calibration it is necessary to obtain exact knowledge of the characteristics of the immersion medium and the target. With this aim, the temperature and salinity of the water was accurately determined, resulting in an estimate of the sound speed of the water. The density and composition of the spheres were examined using laboratory equipment. Moreover, various other sources of variability have been addressed. For the purposes of this work, seven tungsten carbide spheres of different sizes were used to perform inter-comparison calibration estimates. Measured and modeled target strength curves were compared across the bandwidth of 50 to 150 kHz. Comparative results are presented for all the spheres, with the best-case average precision of 0.22 dB being obtained for the 25 mm sphere.

A Knowledge-Based System for Evaluating the Impact of Soil Properties on the Performance of Utility Location Technologies: Design and Case Study

Non-invasive utility location techniques are vital for maximizing the potential of trenchless technologies, especially within an urban environment. This paper proposes the approach of implementing a knowledge-based system (KBS) for predicting the geophysical properties of the soil by taking into account both the geographical and seasonal variation in soil properties. The key motivation for developing KBS as a prediction methodology is the advantage of being able to gather and integrate both analytical models as well as expert knowledge based upon existing and opportunistic data. The design and implementation of this system are presented as a case study for ground penetrating radar, which is mainly affected by the complex permittivity and electrical conductivity of the soil. Soil electromagnetic semiempirical models are implemented to obtain an estimate of the complex permittivity using geotechnical properties obtained in laboratory tests or found on a national database. Hydrology models are applied to account for variations in soil water content and the associated impact on permittivity values due to changes in precipitation patterns. Results obtained from a ground penetrating radar test site with a long-term monitoring station installed are also presented, showing agreement between measured data and KBS output, and demonstrating potential for improving the effectiveness of utility surveys.

Magnetic Field Measurement to Detect and Locate Underground Power Cable

Accurate location of buried cables is crucial for future application of trenchless technologies in urban areas. This paper describes an experimental study on detection and location of underground power cables using magnetic field measurement. To do this, a measurement system is designed to be able to measure the magnetic field of an underground power cable at a number of points above ground. It was constructed using battery powered data acquisition modules connected to a coil array, and controlled by a laptop. The experimental investigation has been carried out in a university car park, where the universitys utility map shows an isolated power cable. The results shows that the measurement system and cable location method predict a reasonable position of target cable.

Disposable stepped-frequency GPR and soil measurement devices

Some geophysical and geotechnical scientists would wish to non-invasively measure the electromagnetic properties of soils using inexpensive, even disposable, technology. They may even wish to develop inexpensive and compact low-power GPR equipment for such uses as teaching and mitigation of construction risks during excavation. To this end, a heuristic comparison is made between a commercial Vector Network Analyser (VNA) and two very low cost VNAs sourced from the amateur radio community. The results are used to illustrate the potential for technology transfer from amateur communications to the GPR community, in order that a wider range of technologies be available for inexpensive implementation in GPR and soil spectroscopy studies. It will be shown that even very low-cost gain and phase detection semiconductor devices can be used to develop simple GPR and soil measurement systems capable of being used in the field to compliment GPR survey interpretation, as well as for standalone soil monitoring.

Robust time‐division channel‐access approach for an ad hoc underwater network

An ad hoc underwater network is formed by a cluster of stationary nodes that can act as a source, destination, or a relay, in which data packet usually travels across multiple hops. Using a time-division scheme where the propagation delay between the nodes is used as a packet queuing buffer optimises throughput. This requires accurate knowledge of the relative ranges of all the nodes, a high level of accuracy in time-synchronisation, and restricts changes in the position of the nodes especially in the absence of a central server or master node within the network. A method that offers greater robustness is by using a time-slotted approach, where each node is offered a time-slot sufficient for one transmission to reach its maximum effective range. A passive acknowledgement scheme is implemented where a node listens for acknowledgement when the transmitted is being relayed. Nodes monitor other time-slots for the opportunity to contend for idle slots in order to enhance throughput. Results obtained from simulations demonstrate that this method is robust in supporting changes in the relative distances between the nodes, and can operate with a time synchronisation error of up to 1 second.

Mapping the Underworld: A Step-Change in the Approach to Utility Location and Designation

Trenchless technologies (TT), unlike open cut trenching, offer the potential to install, maintain and refurbish buried utilities without the need to close long stretches of carriageway. Recent studies indicate that carbon emissions associated with trenchless installations are far smaller, and trenchless installations are more sustainable, than trenching. Yet utility companies, and their contractors, routinely shun trenchless technologies due to the perceived risk of damaging previously undetected third party assets. Mapping the Underworld (MTU) seeks to create a multi-sensor tool, and a new philosophical approach to underground mapping, to mitigate such risks and facilitate the routine adoption of TT. The novel approach is now being developed through the proof of concept stage towards field trials and the results of these proving trials form the basis of this paper. Moreover such street works, like all construction, repair, renewal and maintenance projects, must be reviewed in terms of a sustainability assessment framework to explore their real costs and benefits to the society on behalf of which, as ultimate ‘users’ of the facilities, the works are being carried out. This paper seeks to integrate the findings of a highly multi-disciplinary technology-based project with a wider research programme on the context of effective and efficient working in the streets. The lessons drawn from this programme of research extend to all aspects of pipeline engineering.

Robust Weighted-mean Approach for the Evaluation of Ground Improvement Columns Using Surface Wave Analysis

This paper demonstrates the application of surface wave analysis specifically for the evaluation of ground improvement columns, and considers the susceptibility of phase measurements to noise associated with this technique. This is addressed by introducing a robust approach of calculating the phase velocity based upon a weighted-mean approach that uses the signal-to-noise ratio (SNR) of the signal as a variable cost function to obtain an optimal phase velocity estimation. Experimental data was collected from a laboratory scale setup of a 0.1 m diameter x 0.15 m depth gravelly-sand column installed within a 0.6 m x 0.3 m x 0.3 m block of homogenous kaolinite-clay. Results from the measurements indicated Rayleigh-wave phase velocities of 59 m/s and 110 m/s for the clay and column respectively. The weighted-mean approach demonstrated consistently more accurate phase estimation as compared to the case of a rigid threshold approach.

Pipeline Engineering in the Ground: The Impact of Ground Conditions on Pipeline Condition and Maintenance Operations

The ground in which utility service pipelines are buried inevitably controls, to a large degree, the structural performance and progressive deterioration of the pipelines themselves. In a parallel programme of research to the UK Mapping the Underworld (MTU) project, a study of the fundamental properties of the ground, and how they change with the seasons and local physical and chemical contexts, is being conducted at the University of Birmingham, UK. While the results of this study feed into both the operational protocols for the MTU multi-sensor location device and the associated knowledge based system (KBS) that is being created to aid its deployment (both topics being the subjects of separate papers to this conference), the suite of complementary research projects on the ground and its properties provide valuable insights to the pipeline engineer. Geophysics is being used by the research team to explore the state of the ground with the aim of highlighting areas of concern for the structural health of pipelines buried in the ground. Studies of cast iron pipeline corrosion mechanisms have focussed on the changes that the reaction products cause to the surrounding soils, with a particular emphasis on clay soils, and one interesting finding is that these clay-iron reaction products can make the pipelines ‘invisible’ to standard geophysical location devices. Moreover there are other features in the ground that are being targeted (voids, ground wetting and softening due to leakage, ground weakening due to progressive erosion), and these features effectively make the ground more or less ‘visible’ to geophysical technologies. Alongside this work, bespoke tests have been developed for use on site to ‘calibrate’ the geophysics, thereby enhancing the signatures of the features. This paper introduces these parallel research projects and draws out the important findings for pipeline engineers charged with establishing the condition of existing buried assets.