One critical issue in network real-time kinematic (NRTK) is the interpolation of atmospheric delay for user stations. Some classic interpolation algorithms, such as linear interpolation method (LIM), ignore the strong correlation between tropospheric delay and height factors, and the interpolation accuracy is poor in areas with large height difference. To solve this problem, a troposphere modelling method based on error compensation, namely ECDIM (Error Compensation-Based DIM), is proposed, and this method can be applied to both conventional single Delaunay triangulated network (DTN) and multi-station scenarios. The results of California Real Time Network (CRTN) with large height difference show that compared with LIM, the overall modelling accuracy with ECDIM has been improved by 50.1% to 67.3%, and especially for low elevation satellites (e.g., 10–20 degree), the accuracy is increased from tens of centimetres to a few centimetres. At user end, the positioning error in up direction with LIM has an obvious systematic deviation, and the fix rate of epoch is relatively low. This situation has been improved significantly after using ECDIM. The results of Tianjin Continuously Operating Reference System (TJCORS) show that in areas with small height difference, both methods have achieved high precision interpolation accuracy, and the positioning accuracy with ECDIM in up direction is improved by 21.2% compared with LIM.

The traditional non-adaptive Kalman filter includes models of the error characteristics of the navigation aids in use and such filters are very successful, so long as their model assumptions approximate to the true error characteristics sufficiently closely. However, for any filter there will be times when the environment changes and one or several aids will have errors which are not consistent with the assumed error models. It is necessary to consider carefully the sensitivity of the filter to such changes and, where a significant reduction in performance ensues, modifications to the filter are necessary.

This paper introduces a Kalman filter which monitors the behaviour of internal variables to detect and characterize any model imperfections. The filter will then adapt its internal model of the environment accordingly. The discussion is restricted to the development of a navigation filter for integrating dead reckoning (EM log and gyrocompass) and Omega data. The principles are the same for any filter and details regarding similar analysis involving the use of other aids, for example Satnav and Decca, have been developed in a similar way.

Before implementing any filter it is necessary to understand the behaviour of the measurement errors. For the dead reckoning and Omega aids this behaviour is described in section 2, while section 3 outlines a filter for integrating these aids and introduces the problems of model imperfections.

It is the common practice to draw great-circle tracks on gnomonic charts, on which they appear as straight lines, to pick off the latitudes of intermediate points where the track is intersected by the charted meridians, and finally to transfer the pairs of coordinates thus measured to a Mercator chart. The purpose of this note is to present the derivation of some formulae by means of which the coordinates of points along the track may be calculated very easily.

It is well known that many collisions occur because one ship turns right whilst the other turns left when in close proximity to one another. Little is known as to why this occurs and, although some simulation models have been established using entropy theory, the problem remains unsolved.

In this paper, an assessment model for uncertainty is reviewed briefly. The concepts of uncertainty and uncoordination of mariners' behaviour in collision avoidance are discussed. A simulation model in conjunction with a DCPA (distance to the closest point of approach) decision-making model using fuzzy programming is introduced to discuss coordination.

This second Matthew Flinders Memorial Lecture, in a series sponsored jointly by the Royal Institute of Navigation and the Hydrographic Society with the cooperation of Lincolnshire and Humberside Arts was presented at the University of Hull on 11 May 1983 with Sir John Dudding, Chairman of Lincolnshire and Humberside Arts in the Chair. The first lecture, presented by Rear-Admiral G. S. Ritchie in April 1974 (Journal27, 3) on the bicentenary of the birth of Matthew Flinders, described the hydrographic work of this exploring navigator. Miss Ferrar concentrates on the graphical records of Flinders's Australian voyages.

When Marco Polo made his journey to China, overland from Venice in the thirteenth century, the lands around the Pacific Ocean were wholly unknown to Europeans. But the silks and spices with which he returned sowed the seeds of the quest for a sea route to the ‘Spice Islands’ which was to be one of the mainsprings of exploration for nearly 500 years. The Spaniards crossed the Atlantic. But instead of finding themselves on the coast of Asia as they had expected they discovered the lands (and the wealth) of the Aztecs and Incas, and their explorations extended along the Pacific coasts of Central and South America from Mexico to Peru. The Portuguese found their way around southern Africa and across the Indian Ocean to South-east Asia, where they attained their objective and established a lucrative trade with the Spice Islands. Sailing ship routes depend upon the direction of prevailing winds, so the outward voyage took them eastwards from the Cape of Good Hope and then northwards to their destination. The homeward crossing of the Indian Ocean was in more northerly latitudes.

The first scientific instrument to be designed specifically for use at sea was the mariner's astrolabe. The cross-staff or Jacob's staff had been used by astronomers since the Middle Ages, and the magnetic compass used by navigators had long been familiar as an aid to land travel, a means of setting portable sundials, and in the east, a device for divination.

Significant developments have taken place in navigation and positioning techniques at sea. These include radio, acoustic and inertial methods, and satellite based techniques. The latter consist of the Transit Doppler system, which has now been in operation for over 20 years, and the Global Positioning System which is due to be inaugurated in the early 1990s. These various systems are described in the paper, and their marine engineering, geodetic and geophysical applications discussed. The paper is based on a lecture presented at the Oceanology International Conference held at Brighton in March 1986.

In many aviation and nautical contexts, single manning is common. Some aircraft and some vessels are designed for single manning with no choice. Others can have multiple or single manning, usually depending on such factors as operational requirements, mission objectives, intended human roles, task demands, workload, envisaged mission duration, and environmental conditions.

Recently, there has been wide-spread interest in the use of the Global Positioning System (GPS) for precision approaches in a civil aviation environment. However, most of the work to date in Europe and North America has treated a GPS/inertial reference system (IRS) combination as the source of guidance for this phase of flight. Since the US has a very large general aviation population, the FAA is very interested in determining the role of a stand-alone implementation of differential GPS (DGPS) as a navigation sensor for precision approaches. This paper has two parts: a summary of the analysis of this application of DGPS; and a discussion of the navigation satellite test bed that is under development at the FAA's Technical Center.

The first part contains proposed accuracy, integrity and availability operational requirements, and their air traffic implications. A stand-alone DGPS concept is developed, and analysed. The major results of the analysis indicate that stand-alone DGPS may not fully meet Category I (CAT I) accuracy requirements. The results of the analysis are then used to provide the rationale for the major recommendation: that FAA pursue an implementation of a wide-area DGPS (WADGPS) to achieve a Near CAT I precision approach capability. The second part of the paper discusses the three-phase navigation satellite experimental programme that is being developed to acquire the data to validate the enhancements to GPS, including a GPS Integrity Channel (GIC) and WADGPS. The objectives of each of the experimental phases are presented and discussed. Then the experiments of Phase I that address GIC/WADGPS are discussed.

For mobile 3-D radar installed on a gyro-stabilized platform, its measurements are usually contaminated by the systematic biases which contain radar offset biases (i.e., range, azimuth and elevation biases) and attitude biases (i.e., yaw, pitch and roll biases) of the platform because of the errors in the Inertial Measurement Units (IMU). Systematic biases can NOT be removed by a single radar itself; however, fortunately, they can be estimated by using two different radar measurements of the same target. The process of estimating systematic biases and then compensating radar measurements is called error registration. In this paper, the registration models are established first, then, the equivalent radar measurement error expressions caused by the attitude biases are derived and the dependencies among attitude biases and offset biases are analysed by using the observable matrix criterion. Based on the analyses above, an Optimized Bias Estimation Model (OBEM) is proposed for registration. OBEM uses the subtraction of azimuth and yaw bias as one variable and omits roll and pitch biases in the state vector, which decreases the dimension of the state vector from fourteen of the All Augmented Model (AAM), (which uses all the systematic biases of both radars as state vector) to eight and has about 80% reduction in calculation costs. Also, OBEM can decrease the coupling influences of roll and pitch biases and improve the estimation performance of radar elevation bias. Monte Carlo experiments were made. Numerical results showed that the bias estimation accuracies and the rectified radar raw measurement accuracies can be improved.

In this note the Middle Latitude Rule is derived. Namely, to reach Great Circle vertex in two steps such that the total distance is a minimum, an initial rhumb line course equal to the orthodromic course at Middle latitude is to be used. The shortest distance is achieved if the rhumb line course is altered towards the vertex at the orthodrome-loxodrome intersection point.

When the satellite era commenced more than a quarter of a century ago, one could hardly foresee the world wide revolution it heralded in the development of aids to navigation for merchant shipping. However, early investigations into the possible application of satellites to maritime needs led to an understanding of the powerful potential of satellite techniques for navigation. It became clear that if the international maritime community was really interested in a global all-weather, high-precision and commercially viable navigation system; such a system could only be satellite-based. This is evident from the situation that has recently arisen in IMO, where after exhaustive discussion on the mandatory carriage of electronic position-fixing equipment on ships in designated areas, the organization could not express a preference for any particular aid, until it was decided that efforts should be made to develop a global satellite navigation system capable of meeting a new standard of navigational accuracy. Moreover, in preparing the navigational accuracy standard, account was taken of experience gained with existing satellite navigation systems.

The Dover Strait is not the most congested stretch of narrow water in the world but it is the gateway used by ships of almost every kind on passage to and from nearly all the important ports in northwest Europe, Scandinavia and the United Kingdom. While the recent increase in shipping may not continue at its present rate, the modern trend towards larger vessels and higher speeds has enhanced the hazards to navigation in narrow waters and port approaches, while the volume and nature of modern cargoes have dramatically increased the risk of widespread pollution in the event of any major snipping casualty.

Jet streams are fast moving air streams which appear at times in the levels between 15,000 and 40,000 feet; they are located in the tropical air above the polar front. In this paper examples are given and certain occasions are noted on which they have seriously influenced air navigation.

Early in 1948 when a few charts of the 225 mb. level were drawn to show temperature variations over an air route it was noticed that a very strong stream of air was seen along the line where the tropopause appeared to cut that level. This stream seemed of very considerable length and little width.

The author is Professor of Oceanography in the School of Engineering and Science of New York University and this paper was prepared for the Imco joint ad hoc group for the study of external forces affecting ships. Reviewing the circumstances attending the loss of the trawlers Blue Crusader and Boston Pionair in 1965 he attributes them to high pyramidal seas caused by the crossing of wave trains refracted in water of varying depth. The use of model experiments, air photography and laser altimeters is suggested for verifying the theoretical conclusions, in the light of which corrective measures might be taken when navigating under such conditions.

In the discussion which followed the Institute's proposal on routing, Captain Oudet proposed that the collision problem should be investigated in other areas where the risk was known to be high. This paper discusses the origin of NEMEDRI routes and the collision problem on specific NEMEDRI routes in the North Sea.

The origin of NEMEDRI (Northern European and Mediterranean Routing Instructions) routes is a matter of history and necessity, some understanding of which is necessary in any analysis of present problems, NEMEDRI routes are those swept routes through declared danger areas due to mining in World War II in North European waters, the Mediterranean and Black Sea. These routes take their name from the NEMEDRI publication issued to mariners giving the relevant hydrographic information for these particular areas. The swept routes and declared danger areas in many other areas, such as the remote Kerguelen Islands, Tonga or off Korea, have no such special publication and are notified in Notices to Mariners. The present navigational significance of the NEMEDRI routes is that they carry a very substantial amount of the world seaborne trade.

In the first of this series of papers, the general principles of costing the effect of air traffic control deviation were discussed. This paper discusses the application of these principles to a model route structure for North Atlantic subsonic jet traffic. It is shown how the, design of an optimum system is related to cost considerations and how the cost depends on variations in traffic intensity and on the level of separation standards in all three dimensions. The work on which the paper is based was carried out at the Royal Aircraft Establishment.

Powered research ships are the basic vessels from which the science of oceanography is conducted. For the investigation of certain surface water problems, however, a large, powered vessel is not the most suitable platform, for, while affording ample accommodation and working space, she may have fundamental faults. Her deck may be far above sea-level so that in bad weather direct observation of marine life is impossible. More important, her mere presence may alter the very characteristics, both physical and biological, which are being studied. Thus her hull, rolling, pitching and threshing in a seaway may appear to some animals as a fearsome intruder. The throbbing of her propeller sets up low-pitched vibrations powerful enough to alert the fish for miles around. The sea close to the engine room becomes warmed and to it is added hot water from the condenser. There is violent water mixing by the bow wave. These factors in combination effectively alter both the sea temperature and the thermal stratification. The ship's wash, thrown away from the sides, may set up a heavy cross sea which distorts the shape of nearby waves, particularly in regard to their steepness and height.

Although GPS positioning errors are now well described, there are still some uncertainties regarding the impact of some rare space weather phenomena on GPS positioning accuracy. Solar eclipses have been considered as one source of such rare events, so the 1999 solar eclipse gave the opportunity to collect horizontal GPS positioning data for further analysis. The results of statistical analysis show no deterioration of horizontal GPS positioning accuracy. Space weather, ionospheric and geomagnetic conditions were also carefully analysed and showed no significant activity. In conclusion, the experiment confirmed negligible impact of the 1999 solar eclipse on horizontal GPS positioning accuracy, and opens discussion concerning application of satellite positioning systems in space and ionospheric weather monitoring.

The NAVSTAR Global Positioning System (GPS) is a satellite-based navigation system that will provide extremely accurate three-dimensional position fixes and timing information to properly equipped users anywhere on or near the Earth. The system will be available continuously regardless of weather conditions and will find extensive utilization in improved weapons delivery accuracies, range instrumentation, &c. Furthermore it will provide an ultimate saving in the number and cost of navigation and position-fixing systems currently employed or projected. It is a Joint Service programme managed by the U.S.A.F. with deputies from the Navy, Army and Marines and the Defense Mapping Agency. The system concept evolved from U.S.A.F. and Navy studies initiated in the mid-1960s. Current programme plans call for the deployment of six satellites in 1977 to permit demonstration and evaluation tests over the continental United States. The system will then be expanded through the deployment of additional satellites into an operational 24-satellite system.