Binary Offset Carrier (BOC) modulation signals have been applied in Global Navigation Satellite Systems (GNSS) because they offer a higher positioning accuracy and higher multipath rejection. However, there is a drawback in that the autocorrelation functions have multiple side peaks, meaning that this technique also leads to the large main peak estimation error problem and a low correlation decision efficiency problem. In this paper, we propose a new Main Peak Extraction (MPE) method for high-order BOC signals to solve these problems. In the new method, the synthesis cross-correlation function is established, and the geometry graph is formatted to calculate the estimation main peak. We eliminate all side peaks and improve the main peak phase estimation precision under the condition that the sub-carrier phase is offset. The results of the simulation demonstrate that the new method can achieve better main peak decision efficiency, side peak cancellation ability and phase estimation performance than traditional methods.

The idea of an ‘Altitude-Azimuth’ almanac is not new though most effort (see this Journal, Vol. 1, 185, 1948; Vol. 2, 285, 1949) has been concerned with the Sun and planets rather than the stars. For the stars the simple problem is that observations are recorded in mean time (say G.M.T.) whereas the positions of the stars depend on sidereal time (L.H.A. Aries) given by: L.H.A. Aries = G.H.A. Aries + west longitude. A full account of star tables (and diagrams) using a mean-time argument (and thus avoiding using the Almanac to give G.H.A. Aries) is given in ‘The Genesis of the E. A.N.T.s’ (this Journal, Vol. 6, 333, 1953).

Navigation safety at sea is vital for each autonomous surface vehicle (ASV), which involves the problem of motion planning in dynamic environments and their robust tracking through feedback control. We present a practical path-planning method that generates smooth trajectories for a marine vehicle traveling in an unknown environment, where obstacles are detected in real time by millimetre wave (mmWave) radar. Our approach introduces a polynomial curve to describe the lateral and longitudinal trajectories in the Frenet frame, known as the ‘motion primitives’, whose combination ensures that the planning area is properly covered. In addition, we can select a feasible, optimal and collision-free trajectory from such a set of motion primitives that is generated by considering the vehicle dynamics and comfort. The capabilities of proposed algorithm are demonstrated in the experiment with static and dynamic obstacles.

The maritime radiobeacon differential GNSS service in Europe has recently been reorganised with the aim of having at least two of the 162 stations serve each critical coastal location. Maritime administrations have now set specifications for the availability and continuity of the service. The paper analyses these requirements, noting incompatibilities between them. It proposes a method of predicting the performance of beacons, employing IALA standards. This takes into account each beacon's own availability, and propagation factors that include groundwave signal attenuation, interference, and skywave fading at night. Availability, continuity and coverage maps produced by the new programs are presented in the paper.

With most tele-operated robots the operator's only feedback is the view from an onboard camera. Live video lets the operator observe the robot's immediate surroundings but does not establish the orientation or whereabouts of the robot in its environment. An additional plot of the robot's trajectory would be helpful for the operator and is sometimes provided, based on GPS. However, indoors where GPS is unavailable, tracking has to rely on dead-reckoning, which is too inaccurate to be useful. Our proposed TelOpTrak method corrects dead-reckoning errors even when only odometry and a low-cost (and thus, high-drift) MEMS-class gyro are available on the robot. TelOpTrak corrects gyro drift by exploiting the structured nature of most buildings, but without having to directly sense building features. This paper explains the TelOpTrak method and provides comprehensive experimental results.

Earlier versions of this paper (Borenstein et al., 2010a), (Borenstein et al., 2010b) were presented at two conferences. The main difference between the earlier conference papers and the present manuscript is that the latter is more comprehensive, more up-to-date, and it presents an entirely new set of experimental results, including results of a live demonstration at the 2010 Robotics Rodeo event at Ft. Benning, USA.

The helicopter traffic over the North Sea is performed in uncontrolled airspace over international waters. The lack of radar coverage makes the establishment of controlled airspace difficult. The development of Automatic Dependent Surveillance (ADS) and use of satellite technology for Navigation, Communication and Surveillance (NCS) have made it possible to evaluate Modified Automatic Dependent Surveillance (M-ADS) as a basis for establishing controlled airspace over remote areas without radar coverage.

The problem of underkeel clearance is not new; since time immemorial navigators have been concerned to know the minimum depth of water in which they can sail with a ship of given draught. Until quite recently, underkeel clearance requirements were determined almost entirely empirically, and in many cases the rule of thumb values used can be shown to be greater than the requirement of navigational safety would dictate.

In the years since the war the pattern of the oil industry has changed and very large ships are now commonly used to carry crude oil cargoes to a large number of ports around the world. It is obvious that use of these ships, with their deep draughts, has meant that a number of expensive dredging projects have been put in hand to provide adequate access to the ports served. Continuing escalation in size means this will probably continue.

Before considering in detail the instrumentation involved, it is necessary to establish first of all what is meant by microwave radiometry and mention briefly its possible applications. A radiometer is a device for measuring heat radiation and the title ‘Microwave Radiometry’ is a little surprising in that it implies heat radiation at microwave frequencies. In fact a consideration of the underlying physics shows that heat radiation and electrical thermal noise are indeed the same phenomenon, although their properties were investigated independently by physicists and electrical engineers. This concept is particularly valuable in microwave radiometry, where the electronic techniques are appropriate to ultrasensitive noise measurements, but the system applications are most easily visualized in terms of heat, or, more particularly, temperature.

The Eva G. R. Taylor Lectures were founded in 1959 to mark the occasion of Professor Taylor's 80th birthday. Following an appeal signed by the Presidents of various learned bodies, including the Institute, it was agreed to endow an annual lecture to be presented by a distinguished scholar in any of the branches of learning to which Professor Taylor made such notable contributions. Rear Admiral Ritchie's lecture was presented at the Annual General Meeting of the Institute held in London on 26 October 1966, with the President, Rear Admiral Sir Edmund Irving, K.B.E., C.B., in the Chair.

Having studied marine statistics for a number of years, especially those concerning casualties at sea and in particular collisions between ships, the opening paragraph of the Traffic Separation Working Group's report (this Journal, 19, 4) is, to say the least, lacking confirmatory evidence on two counts.

I refer to the general statements which allege that:

(i) ‘The main risk at sea today arises not as it used to from stranding and shipwreck, but from collision’.

(ii) ‘In the open sea, where nearly 30 per cent of all collisions occur…’

As both include the words ‘at sea’ or ‘open sea’ it is not unreasonable to suppose that they imply freedom to manœuvre under own power unhampered by depth of water or similar navigational restriction.

This being so, and not an irrational definition of the area of concern to the Working Party, what are the facts and how exactly do casualties at sea compare with those in other areas of marine interest throughout the world.

To find the right answer to the global problem is not easy and there are no short cuts, such as for example making a sample analysis in a limited area where traffic density is high, in order to arrive at fairly large numbers which are then used to deduce the statistical probability applicable to all areas.

For some years the principal maritime nations have provided sea-going and future Masters and mates with some form of radar simulator training. These training courses, although differing in duration, subject material, training method and technique, had one common aim: to familiarize responsible sea-going personnel with radar as an instrument. They taught understanding of the various instrument controls, picture or display interpretation, plotting and anti-collision tactics based on the existing international Rules of the Road and Admiralty Court jurisprudence: and all this for open-sea conditions where the Master is sole master of the situation and with no outside adviser at his disposal. Many Masters and mates have followed these very necessary and useful training courses and many more will undoubtedly follow, for nobody should today go to sea in a responsible position as Master or officer of the watch without such training. Recently, pilot authorities have started to send their pilots to the same courses and again this is a step in the right direction.

A recent survey by Burger and Corbet (Welsh Institute of Technology) has furthermore shown that those trained do not seem to obtain full advantage of the acquired knowledge, once they are back in actual practice. This fact plus the fast technical advances in electronics and consequently new radar techniques should eventually lead to the institution of refresher courses.

In this paper, presented by the International Air Navigators Council, and written by its Executive Vice Chairman, the navigation of the S.S.T. is considered from the practising navigator's point of view. Extrapolating from present procedures the conclusion is drawn that navigation system verification should continue to be the responsibility of flight-deck management, that self-contained D.R. systems should be monitored by an externally referenced aid, that raw navigational data should continue to be available to the flight crew and finally that simplicity and reliability in navigation systems should be preferred to finite accuracy.

Consideration of an environment in which operational data and experience are limited to the military is a difficult assignment at the best of times. In order to discuss, with some degree of intelligence, the long-range navigation system considered desirable in the supersonic environment, we have relied mainly on the process of extrapolation using existing data and operational ‘know how’ to formulate practical guidelines.

This study aims to address the accuracy evaluation problem for rapid transfer alignment with the coexistence of large misalignment angles and uncertain observation noises. For the requirement of accuracy evaluation, complete information in terms of misalignment angles should be estimated during the alignment process. Thus, a fixed-interval smoothing approach is the core of solving this problem. In this paper, a new Divided Difference Filter (DDF)-based an Interacting Multiple Model Two-Filter Smoother (IMM-TFS) is developed to estimate the misalignment angles. The proposed DDF-based IMM-TFS releases the restriction of inverse nonlinearity by using the weighted statistical linearization regression method, and the resulting pseudo-linear model can be used for backward-time IMM filtering. The smoothing step takes into account the merging of estimations and the interaction of multiple models simultaneously. The new smoother is compared with the previous well-known methodologies in simulations. The results show that the DDF-based IMM-TFS can achieve better accuracy for misalignment angles estimation, and has a high efficiency for detecting the changes in a model.

A paper by Captain J. F. Kemp under this title was published in the April number of this Journal together with some comments on these proposals. Further contributions to the discussion and a reply from Captain Kemp are printed below.

In the April issue of this Journal Captain Kemp has put forward a carefully considered proposal for making the Rule of the Road more effective. His proposal is well considered because he is aware of the audacity which its careful presentation conceals; he is also careful to suggest a change in the Rules only as a basis for discussion. His suggestion is precise, for it is simply to extend Rule 18 to all encounters, or in other words to require both vessels, when crossing or overtaking, to rotate the line of sight in the normal direction as required in Rule 18.