Decca Navigator Research Articles

Electronic Aids to Navigation for Fishing Vessels and Other Open Sea Users

Norway has long traditions in the field of navigation for fisheries and merchant marine use. Recently the whole navigation aid situation in Norwegian waters was extensively studied and analysed by a government nominated committee. This analysis concluded with what may be called a national navigation aids plan for Norway. Although this plan is predicted in specific conditions, some of the experiences gained during the implementation of the plan may be of general interest. Complete Decca Navigator coverage of the Norwegian coast was achieved on the 14th of May when H. M. King Olav inaugurated the last four chains. Now transmitting equipment is developed for un-manned (automatic) operation. Results so far are satisfactory and gives better coverage in narrow fjords than expected. The CONSOL system with longer range and lower accuracy need no special receiver and is therefore inexpensive to use. Three stations around the Norwegian Sea, sharing one frequency, are now under construction. Standardization of nav. aid systems may be a benefit, but overall economy is best served if the large number of users can choose a system to fit their needs. For merchant marine world wide use the OMEGA system seems to hold the best promise not withstanding recent developments in satellite and inertial navigation.

Harco—A Computer Based Air Navigation System

HARCO is the name given to certain variants of the Decca Navigator radio position‐fixing system, in the particular context of the navigation of civil transport aircraft: an environment which is making increasingly insistent demands upon the navigational accuracy and flexibility of each individual user of the airspace, and upon the ability of the navigational equipment to operate with the highest possible degree of automation. An indication of the navigational capability required for an aircraft operating in high density upper airspace and in terminal areas is given by the operational specification issued in April 1961 by Eurocontrol, the European organisation for the safety of air navigation, which the Harco system is designed to meet. The terms of the specification, summarised in Table I, are self‐explanatory, with the possible exception of item (a): this is a reference to the fact that radio aids of the ‘point‐source’ type, unless used in conjunction with an airborne digital computer, tie the airways layout to the actual positions of the ground stations or beacons. If additional routes or airways are required or if an airway has to be moved, one or more stations therefore have to be sited or re‐sited and this can impose acute problems especially in or near an urban area.

Why Decca Works

Radio position-fixing systems employing the continuous-wave hyperbolic principle, such as the Decca Navigator and Loran C, are now used by ships and aircraft numbering tens of thousands and the theory of their operation has become part of the syllabus in many courses of instruction on navigational aids. Although accepting that these systems produce position-lines along which the difference in the distance from the user to a master and slave station is constant, and that such a line is obtained by time-difference measurement in the form of phase comparison between the two received signals, it may be asked whether this process is affected by the doppler frequency-shifts that will occur if the craft is moving with respect to the stations. Surely, the question goes, these must complicate or modify the behaviour of the system and give rise to an error unless the receiver is stationary ? It sometimes seems to come as a surprise to learn that, far from being adversely affected by it, the operation of these systems is a practical example of the phenomenon to which Prof. C. J. Doppler gave his name: they work not in spite of his ‘shift’, but because of it.

Navigation Techniques Used in the Thresher Search

the effectiveness of the means employed in the search for THRESHER was related strongly to the quality of navigational control. Loran A, Loran C, Decca Navigator, reference buoys, radar, and navigation by echo-sounding and acoustical ranging were all eventually available to the Research Vessel ATLANTIS II during the period April 11 to May 27, 1963. All navigational data were taken as frequently as possible (every one to five minutes), to provide enough samples for statistical treatment. Especially in the case of Loran A early in the search, this procedure provided closer navigational control than ordinarily would be estimated from the known characteristics of the system. Loran C provided but one good line of position. Combinations of lines of position from different systems were used repeatedly, but not generally successfully. Decca Navigator, buoys and radar, and soundings were the most effective of the tools used by ATLANTIS II. With their use, the positions of known fixed objects, such as contact Delta, could be reoccupied reliably. On the other hand, it was not equally possible to relate the positional data from several ships, probably because of differences in navigational technique. Determining the location of deeply towed search instruments in relation to one's ship was another navigation problem, of equal or greater magnitude, which was solved adequately by a method of acoustical positioning.

Ear‐to‐ground

DECCA‐GENERAL PRECISION EQUIPMENT TIE‐UP. A new Company, General Precision Decca Systems Incorporated, has been formed jointly by The Decca Navigator Co. Ltd. and General Precision Equipment Corporation of Terrytown, New York. The new Company will be licensed under all patents and related know‐how of the The Dccca Navigator Co. Ltd. and will engage in the design, production and marketing of electronic navigation equipment for commercial and military aerospace applications and military marine requirements. Products will include hyperbolic navigation systems, position fixing systems for survey, airborne computers and pictorial displays. The Dccca system is currently being used by the U.S.A.F., U.S. Army and U.S. Navy and by New York Airways for their helicopter operations and in addition the U.S. Coast Guard has recently approved the New York transmitting chain for use by ships. There is little doubt that this joint undertaking between Dccca and General Precision represents a major step forward in the fight for acceptance of the Dccca area coverage navigation system in the United States and throughout the world.

SURFACE‐SHIP GRAVITY MEASUREMENTS IN THE NORTH SEA*

AbstractModern marine gravimeters enable us to measure gravity at sea with a mean error of 2 to 5 mgals, depending on sea conditions and navigational accuracy.Good results could be obtained, even in rough seas, by means of Graf's ASKANIA Sea Gravimeter mounted on an ANSCHÜTZ gyrostabilized platform.When a DECCA Navigator System is used, the gravity measured at the points of intersection agrees within 5 mgals at wind‐force Beaufort 4 and vertical accelerations of about 60.000 mgals.The southern North Sea has been surveyed with VFS “GAUSS”, the research vessel of the German Hydrographic Institute, Hamburg. Since 1959 about 4.000 miles of continuous gravity measurements combined with simultaneous magnetic measurements have been carried out in this area. Here nearly all remote‐control gravimeter stations of the Netherlands Geodetic Commission were passed once or several times. Hence they could be used as basic points. However, there are a few cases in which the Dutch data could not be confirmed.The results are given as a free air isogam map covering the area between the meridian of Greenwich and 8° east, and between 54° and 56° latitude, with decreasing density of the measurements from east to west.

I—An Elementary Compound System

This paper is concerned with combining the information from a ground-based radio navigation aid (the Decca Navigator) with self-contained sources of dead-reckoning such as air data and doppler. The essentially complementary relationship between D.R. devices and a ground-reference radio system can be exploited so as to produce an airborne navigational system whose merit exceeds that of either component individually. There is, of course, nothing new in a proposition of this kind. It is suggested that a combination such as that of Decca and a self-contained dead-reckoning device can usefully be described as a ‘compound’ system since the whole is formed, to quote the relevant entry in Webster's dictionary, ‘by the aggregation of otherwise independent elements’.

The Bottom Fauna Communities and Their Sediment Relationships off the Coast of Northumberland

A quantitative survey has been carried out over an area of about 750 square miles of the North Sea adjacent to the southern half of the Northumberland coast. Bottom samples were obtained with a 0.1 sq.m. Van Veen type grab and supplemented by trawls and dredges. The grab was weighted to 71 kg and fitted with endless warp rig. The position of sampling stations was determined by 'Decca Navigator'. The area with sampling stations and depths is shown in Fig. 1. The bottom slopes gently to a depth of about 70 m. where a trough of deep water, 80-100 m., penetrates down into the area from the Farn Deeps in the North. This deep water ends just south of the Tyne and represents the most southerly limits of the 80 m. and 90 m. contours in the North Sea. The general conditions of temperature and salinity over the area have been derived by averaging the accumulated data of thirteen years observations at the three hydrographic stations marked in Fig. 1. The average bottom temperature conditions are shown in Table 1. The salinity conditions are so stable that they can be discounted as a factor contributing to community differentiation in this area.

Trade Announcements

Mr Eoin C. Mekie, C.B.E., has been appointed to the Board of the Decca Navigator Co. Ltd.

Eurocontrol Navigation System Proposal

THE Eurocontrol Association has requested technical proposals for a navigation system capable of meeting provisional specification of April 5, 1961—the system to be capable of operational use in 1965. The low‐frequency hyperbolic area coverage navigation system, HARCO, has been proposed by the Decca Navigator Co., C.S.F. of France, and Telefunken of Germany, with the co‐operation of the Teleregister Corporation of America, and this article deals with the VORDAC system proposed by Standard Telephones and Cables of the U.K., Le Materiel Telephonique of France and Standard Elektrik Lorenz Aktiengesellschaft of Germany, with the co‐operation of Bell Telephone Manufacturing Co. of America and Nederiandsche Standard Electric Maatschappij N.V. of Holland.

Part II: Approach Guidance

The success of inter-city transport helicopter operation will depend on the ability to fly between small sites in city centres with good regularity. Any compromise, such as moving the site to the outskirts of the city or only being able to fly in fine weather, will destroy the advantage of the helicopter over other forms of transport. During the past decade there has been considerable progress in the improvement of helicopter flying qualities so that it is now possible to specify equipment which will enable a helicopter pilot to control his machine in all visibilities and most conditions of turbulence. Further developments in ice protection will enable the basic helicopter to be cleared as an airworthy vehicle for all-weather flight. However, there still remains the problem of navigation, which becomes particularly acute for the final instrument approach. Existing equipment, in particular the Decca Navigation System, can probably meet the case for aerial navigation at altitude, but to fly down an approach to low altitudes into a restricted site demands a higher standard of accuracy and reliability than is offered by any currently available equipment. This paper only deals with the blind approach down to a height of the order of 200 ft. above the landing pad. To extend this to blind landing would require an even higher degree of accuracy and reliability, which does not seem to be justified until some actual operational experience of a simpler blind approach system has been gained to establish whether or not there is a real need for blind landing. A blind approach system which will permit a cloud break height of 200 ft. to be followed by a visual approach and landing on ground lighting should offer at least as good a standard of weather regularity as is currently achieved by fixed-wing aircraft.

Pictorial Presentation

IT was a black day for the Decca Navigator Company, and for British aviation as a whole, when on April 8, 1960, the Council of the International Civil Aviation Organization decided, by fourteen votes to seven, to recommend the American short‐range navigation system VOR/DME as an international standard. That the decision was based on political expediency rather than technical merit is much to be regretted, for with the growing appreciation of the value of a pictorial display system, and the recent developments announced by the Decca Navigator Company, the gulf between VOR/DME and Decca appears to have widened even further.

Massive upward displacement in the deep ocean

For a third of a century many and varied studies on sea water have been concentrated upon a single accessible shallow-water station in the English Channel, EI, supplemented by more extensive excursions usually designed to test working hypotheses. This concentration of effort has been richly rewarded. In deep-water oceanography a similar approach is appropriate; a standard station, ‘Cavall’ has therefore been selected in the north-eastern Bay of Biscay in 4700 m of water at lat. 46° 30' N., long. 8° 00' W., nominal, a position worked by the Danish Research Vessel ‘Dana’ in 1922 and 1930. It is not only the nearest deep water position to Plymouth but it has best possible coverage by the Decca Navigator system. For our experimental programme it is essential that the station positions be maintained and repeated precisely. To achieve this a working Decca chartlet (Fig. 1) on a scale of 1:20,000 has been prepared for each station from a portion of the Admiralty Decca Lattice chart no. L 1104. On this a circle of radius one mile is inscribed. Throughout operations the ship is maintained within this circle by stopping work when necessary and steaming back on Decca co-ordinates towards the centre, or beyond to pre-compensate expected drift.

The method and use of two-range Decca

Two-range Decca is a variant of the Decca navigator system. It was developed specifically for surveying, and, unlike conventional Decca, which utilizes permanently based transmitters ashore, the master is carried in a ship and the shore-based equipment is designed for portability as well as for the essential accuracy. The method and use of Two-range Decca form the subject of this paper, but a few introductory remarks about the conventional system may be in order. The Decca navigator system, now in use throughout Europe and in eastern Canada, has established itself as an aid to navigation of prime importance both to ships and aircraft. It can also be used effectively for surveying, and this application has been the subject of much work and several excellent publications.

北欧水域におけるデツカ航法図について(日本航海学会第23回講演会)

First we drew the contours of the constant probability density of the ship-position every each existent Decca Chain in the Northern European Waters, using the following formulae: P (P, R)=sinφ_P+sinφ_R-sin(φ_P+φ_R) P (P, G)=3/4 {sinφ_P+sinφ_G-sin(φ_P+φ_G)} P (R, G)=3/5 {sinφ_R+sinφ_G-sin(φ_R+φ_G)} [See Fig.2〜Fig.9 in this paper] Secondly, by means of the combination of the above mentioned contours, we made the practical "Decca Navigation Chart" by which we could select the appropriate chain and pair to find out the most accurate Decca Fix at any position in the ditto Waters. [See Fig.10 in this paper]

デッカ航法の確率密度等価線図について(日本航海学会第22回講演会)

In accordance with our investigation on the contours of the constant probability density of the ship-position regarding several typical forms of the chain of the Decca Navigator System, it is found that the fundamental rules in selecting the most accurate pair are as follows: (A) You should utilize the pair except the nearest slave station, the pair on the opposite, when yon, close to the extension of the base line, enter the wedge-shaped part. (B) The borderline for selecting the most accurate pair near the base line is curved into the side which has a greater angle drawn by the two base lines, in case each neighbouring angle is different. (A)' According to the differences of the lane widths on the base line, the wedge-shaped part in the item (A) should be changed as follows: a) wider to each side, when the opposite pair is (P, R) b) narrower from each side, when the opposite pair is (R, G) c) biased towards the (R, G) side, when the opposite pair is (P, G) (B)' According to the differences of the lane widths on the base line, the borderline in the item (B) should be changed as follows, even when the angles drawn by each neighbouring base line are equal. a) much biased towards the (R, G) side, near the base line <MR>^^^ b) fairly biased towards the (P, G) side, near the base line <MP>^^^ c) slightly biased towards the (R, G) side, near the base line <MG>^^^

Air and Sea Tests of the Dectra Radio-navigation System

The object of this paper is to summarize the results of air and sea trials that have been obtained in the first two years' operation of the experimental Dectra chain in the North Atlantic area. Reference is also made to observations at fixed monitor stations, and briefly to the Dectra data link for air-to-ground transmission of the Dectra fix.Dectra, which stands for ‘Decca Track and Range’, is a long-range position-fixing system derived from the Decca Navigator. Early in 1957 two of the three transmitting stations forming a Dectra chain designed to cover the North Atlantic air routes were put into operation and flight tests began in March of that year; in the following October, air trials started using all three transmissions. Various tests at sea have also been carried out, although on a much less extensive scale than those in the air.

The Decca Navigator system for ship and aircraft use

The paper discusses the present use of the Decca Navigator radio position-fixing system as a marine and aircraft navigational aid. The permanent navigational service currently comprises 12 chains and some 4000 ship and aircraft installations; in addition, mobile chains are used for surveying and exploration. The absence of modulation permits close spacing of the chain frequencies. The receivers contain a reference system giving a common phase datum for all users. The system is a c.w. hyperbolic one in which, in ships, the fixing co-ordinates are normally indicated as phase-meter (Decometer) readings. Aircraft normally use an automatic plotter driven from the receiver by an impulse-motor servo system. There are several different types of airborne receiver, and for certain airborne applications a servo system imparting an inertial characteristic to the displayed data is employed. The system can be combined with a navigational aid of the Doppler type to form the Dian system, and the Dectra long-range aid, also part of Dian, has common ground and airborne equipment with the parent Decca Navigator system. A recent development includes a zone-identification facility and employs a new form of transmission that substantially increases the range at which lane identification is effective at night.

Two-range Decca as an Aid to Hydrography

The conventional Decca Navigator system is of the type in which pairs of stations generate patterns of hyperbolic position-lines. One station, the master, is common to each pair so that a chain of three stations suffices to provide the two intersecting position-lines required for fixing. Among the advantages of this arrangement are the absence of any limit to the number of users of a single chain and the compactness of the position-fixing instrument (the receiver) which can readily be installed in the smallest craft. These two features contribute considerably to the success of Decca as an aid to surveying as well as to navigation.

Application of the Decca Navigation System as an Approach and Landing Aid

This paper is a report on a joint Bell-Bendix-Decca program to investigate the problems of flying a helicopter in remote areas under instrument flight conditions with presently available machines, the Decca navigator system, and other sensory equipment. The approach and transition phase to a remote landing spot under instrument conditions was of particular interest and present information displays were found to be unsuitable. During the development program a system was built, tested, and demonstrated that would allow complete instrument flight, including precise navigation along any desired flight path and ils type approaches to any desired landing spot in an area covered by the Decca navigation system. The program results clearly indicated that: 1) Flight in remote areas under zero-zero conditions is possible today. 2) The Decca navigation system is an excellent navigation, approach, and landing aid for helicopter instrument flight. 3) Unsatisfactory information displays are most responsible for the limited helicopter instrument flight operations possible today. Research programs to develop integrated displays must be continued.