Presently used surveying sensors in directional drilling processes include accelerometers and magnetometers arranged in three orthogonal directions. The magnetometers in these setups are negatively affected by external magnetic interferences induced by various sources. Therefore, expensive, heavy and lengthy protective nonmagnetic collars need to be installed. Fiber-optic gyroscopes (FOGs) in an inertial navigation setup have been proposed as an alternative to magnetometer-based downhole surveying. The present study explored the feasibility of utilizing a FOG-based tactical-grade inertial measurement unit (IMU) as a complete surveying sensor for measurement-while-drilling (MWD) processes downhole. Alignment and real-time navigation under laboratory conditions were demonstrated. Analysis of vibrations and temperature as possible factors limiting the accuracy of the navigation process was performed. Severe vibration effects were reduced using software techniques, and a shock-absorbing housing was suggested. The temperature range of the IMU is limited by the optical components of the device, but dynamic temperature changes within this range did not present a major problem. A downhole sub design demonstrated that the actual integration of the IMU requires only minor changes in the presently used drilling tools. The utilization of a tactical-grade IMU eliminates the necessity of nonmagnetic collars, which results in lower costs and improved accuracy.

FOG-based navigation in downhole environment during horizontal drilling utilizing a complete inertial measurement unit: directional measurement-while-drilling surveying

Microprocessor technology is appearing more often in all forms of offshore instrumentation and systems. Typically, this instrumentation must operate in real time and meet strict throughput and environmental specifications. As real time, offshore, processing requirements place heavier demands on single CPU processing centers the benefits of distributing the workload amongst several CPUs becomes increasingly attractive. An incompletely developed distributed architecture, however, may not provide the expected level of performance desired. A clear understanding of design tradeoffs and implementation considerations is required to ensure a successful implementation. This paper outlines the basic components of distributed systems, such a processors, operating systems, languages, interprocessor communications and the design decisions which effect bus loading, reliability, design flexibility, concurrent task scheduling and ease of software development. Two specific application examples, both using a distributed computer system, are presented, one in the navigation field and the other an untethered, unmanned vehicle control system.

http://ieeexplore.ieee.org/iel6/5451196/25891/01152116.pdf

Using Distributed Microprocessor Systems In Marine Applications

Raw data can be filtered, aggregated, transformed, fused, visualized, and correlated, yet data by itself is of no practical value. For data to be of value it must first be interpreted. Interpretation/analysis is a necessary but insufficient condition for conveying information. The interpretation must impact the behavior of the end user for the data to be truly useful, hence the term actionable intelligence. This forms the underlying basis of all information processing systems: utilize data collected from a variety of sources to piece together a view of the world that enables an end user to make enlightened decisions with respect to this environment. Information processing (IP) systems take various forms, many of which combine technology from several scientific fields. Within the past four decades we have seen IP systems incorporate many technological advances including Bayesian Networks, multihypothesis data fusion, expert systems, artificial neural networks (ANNs), fuzzy systems, and evolutionary algorithms. The ocean sciences have benefited significantly from these technologies as they have provided new solutions to difficult and previously (computationally) intractable problems. This paper highlights some of the major advances in information processing and data fusion efforts in oceans technology over the past four decades, and presents some predictions about future developments in this dynamically changing arena.

Advances in information processing in oceans technology a 40 year review

Temporal and spatial variations in navigation data caused by deterministic and random phenomena can severely degrade integrated system accuracy unless suitable compensation is applied. An estimation procedure capable of modeling the statistical behavior of measurement and system error dynamics during real time operation has the capability of compensating measurements corrupted by stochastic effects. Several candidate estimators are investigated within a marine integrated system environment. A Kalman estimator is shown to provide the strongest benefits. A cautionary note is included concerning the effect modeling errors and numerical effects may have on estimation accuracy.

S. Swift

Papers

Improved navigation accuracy through Kalman filtering