The United Nations Convention on Law of the Sea (UNCLOS) came into force on November 18, 1994 to provide the legal framework for maritime boundary delimitation. Understanding the geomatics aspects of UNCLOS is vital for coastal nations to claim the ownership of the natural resources within the limits of their Continental Shelf. This paper discusses some of the geomatics aspects of UNCLOS, namely the geodetic and uncertainty issues. A case study for Egypt's outer limits is also presented.

This paper reports the development of a DGPS navigation system integrated with altitude aiding. In this system, a digital height dataset is used for altitude augmentation. A two-dimensional (2-D) positioning algorithm is discussed and modified based on previous publications. The developed algorithm was implemented on the Brunel Inverse DGPS system. The performance of the new developed system is experimentally verified and compared with three-dimensional (3-D) GPS and DGPS systems. The experimental results showed 86% availability of positioning services; whereas for the 3-D GPS system alone, the availability was only 63% of time. In addition, the accuracy of the system was improved from 7.1 to 6.1 m (RMS) for GPS and from 6.0 to 5.1 m (RMS) for DGPS when compared to standalone 3-D modes.

The navigational feats of the Vikings and Norse in the Middle Ages have excited much interest and admiration, and we are fortunate that actual sailing directions for their various North Atlantic routes have been passed down to us in the Icelandic sagas. Using statistical data of modern wind conditions, this paper examines the sailing directions to determine whether the sailing times quoted are reasonable for a type of ship that was making these voyages in the Middle Ages. The findings show very good correlation between the calculated times and those of the sagas. The paper goes on to study an apparent anomaly for a particular route quoted in the sagas and concludes that the departure and destination points have probably been misinterpreted in the past.

The motivation for this paper was to provide computer support on the rules for sailing races. A brief overview is given of sailing terminology and racing rules. It is argued that a useful program for the racing rules should run on hand-held devices. The program should support an archive of rule scenarios, race training, self-learning of the rules, and analysis of rule disputes. SailRule is a freely available program intended to analyse and improve performance in applying the racing rules. The SailRule program has been implemented using the SuperWaba programming environment for hand-held devices. The user interface is described for the rules program. An explanation is given of the principles behind formalising and codifying the racing rules so that they can be efficiently implemented. Examples are given of how the program represents and analyses rule scenarios.

The effort to integrate the use of GPS and GLONASS constellations resulted in the production of a special receiver, which can use both constellations in combination. These receivers may be used in GPS only mode, GLONASS mode and combined (both GPS and GLONASS) mode. Utilising this type of receiver, GPS and GLONASS signals were monitored for one calendar year simultaneously in different places in India to study the status of visibility of satellites and the positioning accuracy. The number of satellites in GLONASS constellation gradually depleted from 16 to 7 during the course of this study. So a 3-D solution was rarely possible using only GLONASS satellites. However, appreciable improvement in PDOP was observed in the combined mode. Before the withdrawal of GPS Selective Availability (SA), significant improvement of position accuracy could be observed in the combined mode. After the removal of GPS-SA, the accuracies of the combined mode and that of GPS-only mode have been found to be of the same order. While this does not apparently reflect any advantage, it indirectly confirms that both the GPS and the GLONASS systems have similar limits of accuracy and also confirms that optimal interoperability of two systems has been achieved. These studies reveal that the combined use of GLONASS and GPS will always be beneficial to a varying degree depending on different applications and circumstances.

Collision avoidance remains the most important concern for ships at sea. Despite the electronic equipment now fitted on ships to support the mariner, expert experience is still essential when a ship is in danger of colliding with the others. To include these experts' experiences to resolve the problems of collision, we have designed a fuzzy collision-avoidance expert system that includes a knowledge base to store facts and rules, an inference engine to simulate experts' decisions and a fuzzy interface device. Either a quartermaster or an autopilot system can then implement the avoidance action proposed in the research. To perform the task of collision-avoidance effectively, a robust autopilot system using the state space H∞ control methodology has been designed to steer a ship safely for various conditions at sea in performing course keeping, course-changing and route-tracking more robustly. The integration of fuzzy collision-avoidance and H∞autopilot systems is then proposed in this paper.

When anchorages are arranged in a harbour, the manoeuvering difficulty of a ship navigating between anchored ships should be considered. However, until now, nobody has researched how to design the arrangement of anchorages from the viewpoint of manoeuvering difficulty. In this paper, the relationship between the arrangement of anchorages and manoeuvering difficulty is systematically analysed by applying the Environmental Stress Model to the problems of a ship navigating between anchored ships. Based on this analysis, a method of designing the arrangement of anchorages is considered that ensures manoeuvering difficulty is at an acceptable level for mariners. The distance needed between the anchored ships has been proposed to accord with the length of the navigating ship and the mean length of anchored ships.

This paper describes an ionospheric correction technique for single frequency GPS measurements from satellites in low Earth orbit. The fractional total electron content (TEC) above the receiver altitude is obtained from global TEC maps of the International GPS Service network and an altitude dependent scale factor. By choosing a suitable effective height of the residual ionosphere, the resulting path delay for positive elevations is then computed from a thin layer approximation. The scale factor can be predicted from the assumption of a Chapman profile for the altitude variation of the electron density or adjusted as a free parameter in the processing of an extended set of single frequency measurements. The suitability of the proposed model is assessed by comparison with flight data from the Champ satellite that orbits the Earth at an altitude of 450 km. For the given test case, a 90% correction of the ionospheric error is achieved in a reduced dynamic orbit determination based on single frequency C/A-code measurements.

Recent studies show that basic satellite positioning is reaching its limits in terms of performance improvements. Further enhancements in positioning performance can be based almost entirely on augmentation and procedures supported by other systems. Considering the complexity of the interrelationship with additional systems, intrinsically different solutions are being developed to solve the positioning performance improvement problem. Here we present a new concept in positioning. Dubbed distributed positioning, it merges basic satellite positioning with advanced and assisted positioning procedures. The resulting complex synergy unavoidably includes the use of additional technologies in mobile communications, wireless Internet, and advanced computer systems. The real advantage from the introduction of distributed positioning lies in its capability to provide a significant improvement in overall positioning performance. Latest navigation status and up-to-date local environment models are much easier to apply on rover positioning, compared with classical assisted-GPS positioning procedures. Distributed positioning presents a completely different approach in positioning performance improvement, opening new prospects in research and development not only in the field of the satellite positioning, but also in telecommunications and computer engineering.

Safe and efficient marine navigation in ice-infested waters requires comprehensive and timely information on the sea ice conditions. These include information on the ice concentration and type, ice edge location, icebergs and open leads. The Canadian Ice Service is responsible for providing ice information in Canadian waters, mainly through its daily ice charts. Unfortunately, due to the difference in time between the ice chart production and its use by mariners, the ice information is always out of date. This problem might be overcome by developing a neural network-based system for predicting the ice conditions over time. A supervised neural network is trained to predict the ice conditions at a given location and time using the current ice charts, which are provided by the Canadian Ice Service. The input ice data is mapped to an output vector that gives the predicted ice conditions. The traditional non-modular feed-forward neural network structure failed to map the required function, and hence, was modularized to give better prediction performance. Each neural module was responsible for the prediction of a 5×5 km area, while the ice characteristic of interest was the total concentration.

This paper was first presented at GNSS 2002 – European Navigation Conference – held in Copenhagen, 28th to 30th May, 2002.

At the 5th GNSS Symposium, held in Seville in 2001, the authors presented a paper entitled ‘The Portuguese DGPS network’, which began by addressing the current need for a DGPS service, given the removal of Selective Availability (Moore et al., 2001). In that paper, the benefits of DGPS for mariners, namely in terms of accuracy and integrity, were discussed and presented, in order to show that the option to embrace DGPS was, and is, still valid because it can provide the best accuracy and integrity at sea. However, the accuracy advantage afforded and the integrity check performed by DGPS are only useful if the DGPS service reaches very high standards of availability and continuity. It would be almost useless to have a DGPS service with low availability and continuity, because it could mean a ship losing the differential corrections in restricted waters, where the service is most needed. In summary, the level of benefit gained from DGPS is directly proportional to the user availability of the service and to its continuity. Having discussed accuracy and integrity last year, this paper covers issues related to availability and continuity (continuity replaced the previously used concept of reliability). The availability and continuity requirements recently adopted by the International Maritime Organization (IMO) and the International Association of Lighthouse Authorities (IALA) are presented, as well as the ways by which DGPS services can meet the very high requirements for the harbour entrance and approach phase of navigation. The concepts used in the Portuguese DGPS network to minimize downtime and ensure the highest reliability and availability, are presented as an example.

It is good to see the COLREGS reappearing in Forum as a subject for discussion. R. W. Cooper (2001) is right to point out the problem inherent in rule 10(j) that one of the vessels in an encounter to which the rule applies cannot be sure whether the length criterion is met or not. Clearly some amendment is desirable.

We have developed a local-area ionospheric time-delay model that consists of nominal and perturbation models. The nominal model describes the trends of ionospheric time delay over 1–2 days and uses nine parameters. The perturbation model describes rapid changes of ionospheric time delay over 2–3 hours and uses six parameters. All the parameters are estimated from raw data measured at one reference station, which has filters to estimate all the parameters of the local-area ionospheric time-delay model. With this model and Black's tropospheric time-delay model, we obtain compensated Differential GPS (DGPS) pseudorange corrections by subtracting the atmospheric time-delay difference between the reference station and the user. We believed that the model could extend DGPS coverage. To check this, we analyzed experimental data. The results show that this algorithm not only improves DGPS positioning accuracy, but also extends DGPS coverage from 100 km to more than 400 km. We named this new algorithm the Seoul National University Differential GPS (SNUDGPS).

This article is the second in a series dealing with the hand-held instruments and techniques navigators have used to find distance.

Warships frequently steam in tight formation in order to concentrate defensive gunfire. It is the Conning Officer's responsibility to keep his ship on station at an assigned range and bearing from the guide ship, usually the flagship of the Senior Officer Present Afloat. This can be an easy task when the fleet is steaming along peacefully, but it becomes a particularly challenging responsibility when the formation is changing course frequently under battle conditions. In such difficult situations, the Conning Officer needs all the help he can get.

In the days before radar, and even now when radar and laser are blacked-out, the Conning Officer had to rely on optical instruments to determine range and bearing. Bearing always has been easy – a pelorus mounted on the wings of the bridge gives bearing quickly and accurately. Measuring range is more difficult. Many ingenious instruments relying on prisms or the doubly reflecting principles of the sextant have been produced to simplify the task of finding distance (Ifland, 2002).

I read the Forum article ‘Removal of an Ambiguity from the Maritime Collision Regulations’ (Cooper, 2001) and make the following comments. As a Royal Yachting Association Yachtmaster Instructor, I find that many people quote Rule 10 of the COLREGS only in part and thus are misled by its intentions.

Finding the distance has always been a challenge to the mariner. What is the distance to the lighthouse at the mouth of the harbour? Am I far enough off the rocks and shoals? My assigned station in the formation is bearing 300°, range 1500 yards from the guide ship, am I on station? What is the range for gunfire to the enemy flagship?