When we started surveying Megalithic sites in Britain we used a cloth tape, but after some years it was realized that it was necessary to be more precise and now we use a steel tape for the important sites. Similarly with astronomy; at first we considered it sufficiently accurate to work to ¼° but now we know that it is advisable to work always to within a minute of arc. This is because we have found out that the erectors of the stones sometimes used distant foresights, either artificial or natural, and by using these they could get an accuracy of better than a minute. The method of observing was for the operator to watch the edge of the celestial body grazing a foresight or running down the edge of a hill. He moved sideways until he got exact coincidence and then marked the position. This first came to our attention when we measured up the site at Ballochroy on the west side of Kintyre.

Maritime traffic has significantly increased in recent decades due to its advantageous costs, delivery rate and environmental compatibility. With the advent of the new generation of marine radars, based on the solid-state transmitter technology that calls for much longer transmitted pulses, the interference problem can become critical. Knowing the positions and the heights of the ships, the mean number of the vessels in radar range can be estimated to evaluate the effects of their mutual radar interferences. This paper aims to estimate the probability density function of the mutual distances. The truncation of the density function within a limited area related to horizon visibility leads to a simple single-parameter expression, useful to classify the ships as either randomly distributed or following a defined route. Practical results have been obtained using Automatic Identification System (AIS) data provided by the Italian Coast Guard in the Mediterranean Sea.

This paper discusses the necessity and feasibility of the application of Pulse Doppler Radar in vts through analysing the limitations of the non-coherent, single frequency, radar and the advantages of PD radar.

Increasing the stability and reliability of navigation for mobile objects of different classes is becoming increasingly significant. Satellite navigation systems have a fundamental defect: a vulnerability to hacking and spoofing. Observation of the horizon line is significant for two applications. The first is stellar inertial navigation systems. In this case, the horizon line can be used for local vertical estimation. Errors in local vertical estimation directly affect coordinate errors. The second is correlation-extremal navigation based on the observed horizon line shape (when islands or continents are observed from aerial vehicles). In both cases, instability of the horizon line produces navigation errors. A measurement procedure for horizon line position estimation was proposed and realised. Around-the-clock horizon line shooting was undertaken in 2013. Processing of the results shows a horizon line direction instability of about 5–7 angular minutes during the day time.

Self-organising radio systems have been proposed for aeronautical and maritime communication, navigation and surveillance applications. In aviation, the introduction of the VHF Data Link (VDL) Mode 4 is currently being discussed, while the implementation of Automatic Identification Systems (AIS) is planned in the maritime domain. Operating in an autonomous mode, a self-organising radio system employing Time Division Multiple Access (TDMA) does not require a terrestrial infrastructure, such as base stations. The concept of self-organisation is based on the cooperative behaviour of a large number of users sharing a common VHF radio channel. Analyses have shown that uncoordinated stations, so-called hidden users, can cause interference in self-organising radio systems. This paper presents two different approaches to autonomous self-organisation together with the results of investigations of intra-system interference. Such analyses may help to introduce potential improvements to the system performance, which reduce the effect of hidden users in this very promising GNSS-based technology.

A theoretical analysis of the effects of dual frequency ionosphere propagation correction on GNSS code tracking noise is presented. The effect on tracking noise of using different combinations of the proposed Galileo signals for ionosphere propagation correction is investigated. It is concluded that, for the open or commercial service user, the Galileo signals E2-L1-E1 near to and around GPS L1 should be used to apply ionosphere propagation corrections to the E5 signals. This produces a tracking noise standard deviation about three times larger than that on an E5 signal alone. An ionosphere correction-smoothing algorithm is presented that reduces the tracking noise on the corrected pseudo-range measurements.

The development of augmentation services, such as EGNOs and WAAS, requires careful modelling and simulation before any deployment of equipment takes place. The ideal location of ground stations, and the potential impact of temporary failures of ground equipment, must be assessed in detail, to ensure that proposed service levels of accuracy and integrity are maintained at all times. The correct analysis of these parameters can only be achieved if the various wide area processing models, and their respective error propagation characteristics, are suitably simulated. This paper describes the use of a sophisticated and versatile suite of GNSS analysis tools in recent studies. It describes the incorporation of realistic error budgets for WADGPS and LADGPS corrections, and the potential use of different combinations of GPS, GLONASS, geostationary and other satellites in both GNSS-1 and GNSS-2.

Readers of Captain Cotter's paper under this title in the April 1976 issue of the Journal may be interested in some evidence that Dutch seamen in the seventeenth century were aware of this phenomenon of ship magnetism.

Abraham de Graaf in De seven Boecken van de Groote Zeevaert, published at Amsterdam in 1658, warns ships' officers taking bearings with the compass-that metal objects in their clothing can seriously deflect the compass, and mentions iron buttons and buckles. This was an important contemporary work on navigation and de Graaf was an examiner of officers of the Dutch East Indies Company from 1679 to 1714.

Many problems in navigation can be best viewed and solved as problems in analytical geometry. We only need to understand the geometry of two ‘navigable’ surfaces; the sphere and the ellipsoid of revolution. The ellipsoidal model is generated by revolving an ellipse about its minor axis and this model is used as a global model for the surface of the Earth. The eccentricity of the meridian ellipse is small (≈0·082) so we sometimes refer to this surface as a ‘spheroid’ since the surface is still ‘sphere-like’. The physical Earth is, in fact, referred to as a ‘geoid’ whose surface is that which approximates global mean sea level. The mathematical representation of the geoid is not trivial and the ellipsoid of revolution is an extremely good approximation to it.

This paper compares the differences between the rhumbline courses and distances calculated by three methods: the classical formula, precise formula and by software contained in a typical GPS receiver. It concludes that, while the calculations made by the GPS receiver are generally more accurate than the classical method, navigators must use Tables of Latitude Parts to calculate rhumbline distances accurately.

Conventional cruise control systems fulfil the function of automatic speed control. A desired speed is selected by the driver, and a control system operates on the throttle to maintain this desired speed. When traffic density is moderate or high, the driver is faced with having to adjust the set speed regularly in order to maintain a comfortable distance from preceding vehicles and will frequently have to brake, disengaging the cruise control. Thus conventional cruise control can become a source of irritation when used in moderate or heavy traffic. If a distance sensor is added to a conventional cruise control system, then it is possible to add distance keeping to the basic speed control function. This forms the basis for adaptive cruise control, which can be further improved if a limited authority braking system is incorporated. Use can then be made of both throttle and brake actuators to control the distance and relative velocities between a vehicle and a preceding target vehicle.

This paper presents further research on the SNUGL pseudolite-based navigation system presented in this journal in 2003. This system has centimetre-level accuracy, but has an error source arising from right-hand circularly polarized (RHCP) transmissions, unlike outdoor Global Positioning System (GPS). The GPS satellites and pseudolites use RHCP signals, and the polarization affects carrier-phase measurements according to the Line-of-Sight (LOS) vectors from transmitters to receivers. The RHCP error is eliminated by a double differencing process in outdoor GPS, but the error remains in the pseudolite-based system because the LOS vectors from transmitters to a reference and user receivers are different for the close transmitter constellations. This paper shows the RHCP effect on the pseudolite-based navigation system through simulations and experiments. It then shows the RHCP-compensation method improves the measurement and position accuracy by over 10%.

This paper considers the issue of operating aircraft through the North Atlantic's Minimum Navigation Performance Specification (MNPS) airspace. Noting that aircraft constantly strive for reduced fuel burn and uplift, it describes how flight operators and pilots conduct safe, efficient flights through the region. Reference is made to mechanisms of the North Atlantic MNPS airspace in terms of its Organized Track Structure and other routes that exist. These different structures emphasize the level of flexibility available. Flight planning procedures and requirements necessary to obtain oceanic Air Traffic Control (ATC) clearances are mentioned, as is an account of how communication and position reporting procedures operate to apply the Mach Number technique. Other aspects of MNPS operations such as ETOPS operational restrictions, meteorological effects, the employment of Reduced Vertical Separation Minima and planned regional changes aim to provide an overview of the MNPS system's current and future air traffic management.

Unlike a direct broadcasting satellite navigation system, the transmitting satellite navigation system developed in China uses transponders onboard communication satellites to retransmit navigation signals generated at a ground master station. The transmitting navigation satellite constellation consists of a number of inclined geosynchronous orbit (IGSO) satellites. Considering China's mainland coverage in the northern hemisphere occupies some 62 degrees in longitude, the inclination of the IGSO satellites cannot be too high, or its signals would not be received by the users in the middle and high latitude areas when the IGSO satellite travels over the southern hemisphere. Meanwhile, the latitude of the most southerly station in China mainland that can uplink navigation signals is about 18°N when the IGSO satellite travels to the southern hemisphere. Therefore, there is a need to consider the IGSO inclination to achieve balance between uplinking high-quality navigation signals and covering the high-latitude area. In this work, the navigation performance and availability of the IGSO satellite are examined when navigation signals are uplinked from the stations Lintong and Sanya.

The History of Air Navigation Group commissioned the author to provide a brief account of airborne DR development by discussing both the methods and the equipment used in the air. This first part covers the period before 1940. The split is arbitrary, although it is obvious from a British perspective that military events around that date had a major impact on the pace of navigation development. However, it is equally obvious that airborne DR developed alongside a worldwide technical and intellectual revolution. This aspect of the story is abstract and involves some conjecture, so the paper takes it for granted and concentrates instead on practical matters. Accounts of air navigators' experiences as well as material on DR theory and descriptions of DR equipment in navigation manuals, journals and various surviving research documents have been used as the source material.

The title, the gift of Frank George, derives from The Troublesome Voyage of Captain Edward Fenton, E. G. R. Taylor's masterly edition of narratives relating to one of the less successful of Elizabethan adventures. Fenton's voyage of 1582, to China and Cathay, was a total failure. But the tale endures.

Mobile satellite communications and navigation are, historically and technically, intertwined. This paper offers a historical perspective on this interrelationship to see if the past provides some guidance to the future.

In the next decade there will be an increasing demand for more accurate self-contained navigation systems due to more stringent air traffic control requirements, particularly with the introduction of the supersonic transport. Although inertial systems have been fairly widely used in military aircraft and missiles, the only self-contained systems in service in civil aircraft are dead reckoning systems based on measuring the aircraft's velocity and heading and drift angle. A big improvement has been effected in the measurement of velocity and drift angle by the introduction of doppler radar. The accuracy achievable with doppler is not matched by the accuracy of existing heading reference systems and the overall accuracy is, at present, inadequate for future requirements.

An inertial navigation system is a possible alternative but its cost will be two to three times that of a doppler heading reference system.

H.M.S. Challenger is one of Her Majesty's surveying vessels. She is a ship of 1140 tons and carries a complement of 96 officers and men. Built in 1931, she is named after her illustrious predecessor in which the wellknown world oceanographic cruise was made in the years 1872–6. This expedition brought back a great wealth of chemical and physical data, and a huge collection of plants and animals from the oceans. These were checked and analysed and eventually, under the guidance of Sir John Murray, who had been a scientist on board, the results were published in fifty folio volumes known as the Challenger Reports. These reports still form, the starting point for the study of the oceans and marine life.