For many years there has been evidence (for instance from pilot balloon ascents and drift of cirrus clouds) of the existence of occasional very strong winds in the upper troposphere. However, it was not until about 1933, that Bjerknes, who had introduced the concept of the polar front during the first world war, produced a map of geostrophic wind deduced from upper-air temperature soundings made at a few scattered stations and showed a core of strong westerly winds at about 12 kilometres in middle latitudes in winter. No further progress was made until during the second world war when a comparatively large number of upper-air stations were set up and it was found that narrow belts of very strong winds were almost always present over some part of the Earth's surface in the 30,000/40,000 ft. altitude band. In 1944–5 American bombers encountered some rather frightening winds over the Japan area and since that time some extensive investigations of jet streams have taken place.

The term jet stream is popularly applied to any strong upper-wind current (of say 80–90 knots) and it is safe to assume that such winds are in fact associated with a jet stream, which may be considered as a narrow tube containing very strong winds embedded in the surrounding atmosphere.

A closed form of an algorithm to determine a Global Positioning System (GPS) satellite's position, velocity and acceleration is proposed, and an Earth Centred Earth Fixed (ECEF) to Earth Centred Inertial (ECI) transformation result using the Civil Navigation (CNAV) message is presented in this paper. To obtain the closed form of the GPS satellite velocity and acceleration determination algorithm using the CNAV, we analytically differentiated the IS-GPS-200F position determination function. The calculated data are transformed from the International Terrestrial Reference Frame (ITRF) to the Geocentric Celestial Reference Frame (GCRF) using an equinox-based transform algorithm that is defined in the IAU-2000 resolution system using the Earth Orientation Parameter (EOP) data. To verify the correctness of the proposed velocity and acceleration determination algorithm, the analytical results are compared to the numerical result. The equinox-based transformation result is compared to simple rotation about the z-axis, which does not use the EOP. The results show that by using the proposed algorithm and the equinox-based transformation together, the user can obtain more accurate navigation data in the ECI frame.

In this paper, a simplified constellation architecture consisting of only two navigation satellites located around the Earth-Moon L1,2 libration points is obtained for the Universe Lighthouse. In order to determine the feasible constellations that can achieve continuous global coverage for lunar orbits, an exhaustive search over all possible combinations of libration point orbits is performed first. With the use of a fitting procedure, amplitude relations between the feasible L1 and L2 libration point orbits are derived by polynomial interpolation. After that, a cislunar navigation simulation is conducted to verify the navigation performance of the candidate two-satellite constellations. The final Monte Carlo simulation results indicate that the simplified system is available for cislunar navigation and the best accuracy of a few tens of metres can be achieved for both the trans-lunar cruise phase and lunar orbit phase.

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.

Carrier-phase inter-frequency bias (IFB) exists in GLObal NAvigation Satellite System (GLONASS) baselines when receivers of different brands are used. Those biases need to be calibrated in GLONASS data processing to derive precise fixed solutions. Consequently, the accuracy of the IFB calibration affects ambiguity fixing, and low-accuracy IFB values in the calibration will degrade the positioning results. Hitherto, at least two IFB rate value sets for various receiver brands have been given in previous studies. Some of the differences between the value sets exceed 2 mm/FN (frequency number) and the effects of those differences on ambiguity fixing have not been investigated until now. This study showed that ambiguity fixing in GLONASS single-epoch positioning is very sensitive to the accuracy of the IFB rates. Even errors of millimetres can seriously lower the empirical success rate. The short baselines from the Global Navigation Satellite System (GNSS, which includes Russian GLONASS) networks of the International GNSS Service and the Regional Reference Frame Sub-Commission for Europe were employed to obtain more accurate IFB rate estimates with the proposed two-dimensional particle filtering. Afterwards, the IFB estimates were statistically refined by the least-squares method. Experiments showed that when the refined IFB rates were used in the IFB calibration, the empirical success rates of ambiguity fixing in GLONASS single-epoch positioning were largely improved compared with the values given before, improvements such as 20·6% for a Septentrio and Leica receiver combination.

Mr. Wilkinson's paper, which was presented at a joint meeting of the Institute and the Royal Institution of Naval Architects in London on 7 January 1971, with the President, Rear-Admiral G. S. Ritchie, C.B., D.S.C. in the chair, will be published in full in the Journal of the Institution, illustrated with diagrams and inventories tracing the evolution of the ship's bridge and wheelhouse in relation to advances in technology, ergonomic factors and manning policy. A comparison is made with the design of aircraft flight decks and the cabs of diesel-electric locomotives. The value to the naval architect of manœuvring and handling simulators is emphasized. The paper and the ensuing discussion are summarized below.

Wing Commander Anderson has drawn attention to the fact that the distribution of the larger navigational errors is frequently observed to be non-gaussian in character. He raises the point whether this can be accounted for by the generation of such errors in succession, rather than simultaneously. The successive generation of navigation errors arises through the error incurred on a particular leg being distributed about a mean which is dependent on the error up to the end of the previous leg.

When planning the replacement of an existing shore-based radar advice chain, which may have admirably served the port area under consideration for the past fifteen or twenty years, a number of basic elements have to be reviewed. The review and the ensuing process of analysis should be steps towards the adoption of a basic philosophy for the eventual development of a replacement system; this is necessary to judge requirements in relation to the many possible solutions, ranging from a simple shore-based radar advice service to sophisticated vessel traffic management systems. Elements for consideration include:

(i) The area to be served, present and future.

(ii) The traffic pattern, present and future.

(iii) The technology available or under development.

(iv) The other operational and administrative services available to shipping.

(v) The quality of manning and manning scales.

(vi) The economics of the shipping industry.

(vii) The cost of the new system.

(viii) The distribution of this cost over shipping and the community in general.

(ix) Legal aspects.

Besides these factual considerations and their analysis we should develop a philosophy regarding the aims of the system, which could be an improvement in port operation efficiency, in traffic safety, or in vessel turn-around time. The realization of these aims will probably result in economic benefits both for the port and for shipping and these will have to be weighed when investigating the distribution of system cost over shipping and the community in general.

Improved radar surveillance for air traffic control can be obtained by the integration of radar systems. Integration, however, might cause the delay of radar information, which would hamper the air traffic controllers in their work. To estimate the delay, a mathematical equation to assess the amount of radar information causing this delay has been deduced from the properties of the behaviour of air traffic. The mathematical equation has been tested using results obtained from operational secondary surveillance radar in the Netherlands.

This note on the distribution pattern of some Omega observations is based on a study of the phase differences observed at the Faculty of Fisheries at Hokkaido University (41° 48·4′N., 140° 43·3′E.). The A—D pair was investigated continuously, at half-hourly intervals, from i February 1974 to 31 January 1976, the A—C and C—D pairs from 1 January 1975 t o 31 December 197J and the A—H and D—H pairs from 1 January 1976 to 31 December 1976.

In June 1955, Canadian Pacific Airlines inaugurated a regular scheduled service between Vancouver and Amsterdam via the polar route. The Company had a wealth of northern experience which was of immense operational value on the polar route. In addition to its overseas services, C.P.A. has operated regular flights for many years to far northern parts of Canada and some of the group of companies which amalgamated to form C.P.A. in 1942 had arctic experience dating from the days when commercial aviation was in its infancy. One aspect of navigational experience which has helped its navigators on many occasions has been the map reading talents of the former bush pilots who show an astonishing ability to locate themselves visually over country which is mostly water, and where one lake looks much like every other lake.

The lives of sea turtles consist of a continuous series of migrations. As hatchlings, the turtles swim from their natal beaches into the open sea, often taking refuge in circular current systems (gyres) that serve as moving, open-ocean nursery grounds. The juveniles of many populations subsequently take up residence in coastal feeding areas that are located hundreds or thousands of kilometres from the beaches on which the turtles hatched; some juveniles also migrate between summer and winter habitats. As adults, turtles periodically leave their feeding grounds and migrate to breeding and nesting regions, after which many return to their own specific feeding sites. The itinerant lifestyle characteristic of most sea turtle species is thus inextricably linked to an ability to orient and navigate accurately across large expanses of seemingly featureless ocean.

In some sea turtle populations, migratory performance reaches extremes. The total distances certain green turtles (Chelonia mydas) and loggerheads (Caretta caretta) traverse over the span of their lifetimes exceed tens of thousands of kilometres, several times the diameter of the turtle's home ocean basin. Adult migrations between feeding and nesting habitats can require continuous swimming for periods of several weeks. In addition, the paths of migrating turtles often lead almost straight across the open ocean and directly to the destination, leaving little doubt that turtles can navigate to distant target sites with remarkable efficiency.

A geometric approach to Low Earth Orbiter (LEO) precision orbit determination (POD) based exclusively on triple-differenced GPS carrier phase observables is presented. The algorithm is fast and efficient because there is no ambiguity-resolution requirement, which is a complicated and time-consuming task for long-range kinematic GPS. However, the triple-difference kinematic LEO POD requires careful screening for cycle slips, as the orbit quality depends on the accuracy and the geometry of the observations. It is shown that the signal-to-noise-ratio (SNR) combined with residual screening offers a good approach to data cleaning. Data from a CHAMP (Challenging Minisatellite Payload, altitude ~450 km) mission are used to present the accuracy, speed and efficiency of the processing algorithms. The methods of data screening and the effects of geometry on the orbit quality are discussed and the final achievable accuracy including the limitations and benefits of this method are quantified. It is demonstrated that the triple-difference method offers short processing times and is currently capable of achieving a 3D RMS fit to the dynamic orbit of 15–30 cm and 1 mm/s to the velocity.

High-precision ‘autofarming’ makes possible farming techniques previously impractical using metre-level Differential GPS-based control systems: techniques such as tape irrigation, the elimination of guess rows, and precise contour farming. A Carrier-Phase Differential gps positioning and attitude system with centimetre-level and 0·1° accuracy was installed in a large farm tractor. Four types of trajectories (lines, arcs, spirals, and curves) were identified as basic building blocks necessary to generate a ‘global’ trajectory for a realistic autofarming path. Information about each trajectory type was translated into reference state specifications that a linear controller used to control the tractor over velocities between 0·7 and 2·8 m/s to within approximately 6 cm (1 σ) without implement and 10 cm (1 σ) with implement on sloped terrain using a previously developed tractor model. These results are a significant step towards a realistic autofarming system because they not only demonstrate accurate control over various realistic operating speeds but over different types of trajectories necessary for a commercial system.

The basic idea of a dead reckoning personal navigator is to integrate incremental motion information in the forms of step length and step direction over time. Considering that the displacement components are estimated for each step-cycle, it is essential to monitor the integrity of these parameters; otherwise, the error accumulation may render the system unstable. In this paper, a two-stage Kalman Filter (KF) augmented by a neural network is developed to facilitate integrity monitoring. The preliminary results, obtained from several tests performed on simulated and real-word data, indicate an 80% success rate in integrity monitoring.

It has for some years now almost been folklore that the marine traffic situation in the Dover Strait is one of great potential danger. Very considerable efforts have been made to alleviate the situation. There is a complete traffic separation scheme (the first in the world), there is continuous radar surveillance both from England and France, there are routine broadcasts on v.h.f. to warn mariners of any navigational problems, and there is now a system whereby certain ships report-in. Concurrently with all this activity, the accident rate has dropped significantly over the last decade, especially in fog, and it is a reasonable inference that the reduction in the number and severity of accidents is attributable to this activity.

But patterns of navigation change, and it is necessary for marine administrators to be aware of problem areas as or before they arise so that marine management measures can be introduced when appropriate. Factors to be taken into account are the volume and characteristics of the traffic, the difficulty of navigation and the accident record. One of us has drawn attention to the traffic situation off East Anglia and suggested that a prima facie case for some remedial measures had been made. This paper examines the available evidence in more detail.

First, an account is given of the accident record in the area under consideration (Figs 1, 2) over the last 10 years. Both the numbers and severity of collisions and strandings are discussed.

Of immense importance to nautical astronomers are tables of trigonometrical functions. The history of these begins with the table of chords first suggested by Hipparchus two centuries before the beginning of the Christian Era. The earliest table of chords extant is that computed by Ptolemy (fl. c. 150 a.d.) whose table, true to the sexagesimal tradition, is based on the division of the radius of a circle into sixty parts. The first table of half-chords, or sines, is supposed to be of Indian origin and to date from the sixth century; but credit for being first to use a table of half-chords for solving spherical triangles belongs to the Arab mathematician Albategnius who flourished during the tenth century. The first printed table of sines, according to De Morgan, is a small work giving sines to each minute of arc from 0° to 90°, undated and unsigned but evidently published before 1500.