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Contents
1
'J’ _
nrror‘st Weapons and the Terrorist Threat
s*gn Dwight L. Gertz, U. S. Navy
% Ensi, Sharks:
113
Navy Countermeasure Research 113
'' Captain Charles A. Barton, U. S. Navy (Retired)
^'fiega: A Status Report 118
rLCaPtain Charles W. Koburger, Jr., U. S. st Guard Reserve
D,
PasSl
the r
0j. Clty that bustles below. Hundreds in th°usands men and women live
b,
the ^'n£s underneath the flight path of ascending aircraft. In one fourth- ry apartment, three young men open closet door and remove something k lch would remind a movie buff of the a*ooka he had seen in a late show war
Vle- They slide the window open and c’
Tty
°2ens of airlines and governments thgratC t^le ^ig jets which take off from par airPort m a steady stream. The de- 0j- Ure of each is pinpointed by the roar asengines and the flashing of lights 1( roars into the sky. The pilots and engers can make out only hints of
. e sprawling blocks of apartment
T;tch the planes—E1A1, Lufthansa, A- and Aeroflot—each a clearly rked representative of an independent 10n- As the marked aircraft arches crhead, they take aim at the looming sUhouette Th *
ane professional naval officer spends tifrCit 1'1S nme nervously eyeing
sbips, hardware, and expertise of his ential enemies. In recent years, this tention has focused, for U. S. naval
officers, on the rapidly improving Soviet Navy. In our concern for this massive challenge, we must guard against a tendency to forget that the goals of war are political and that these goals may be achieved by forces other than the regular military establishments of the combatants.
In the gray area between peaceful politics and war live numerous organizations capable of contributing to the achievement of national goals. Although this has never been a secret, it is sometimes forgotten that these organizations are improving their tactics and arms inventories in much the same manner as the world’s more conventional military forces do.
A guerilla band cannot defeat a modern naval force, but it can inflict an embarrassing loss on an individual component unit, or it can use an attack on a civilian target to drastically alter the political environment in which the conventional fleet operates. For this reason, it may be interesting to see what sort of improvements have been made in the terrorist arsenal.
It would not hopelessly threaten plausibility to discuss the possibility of nuclear weapons or other exotic weaponry falling into the hands of a terrorist group. Both the spy thrillers and sober military analyses have brought this problem to light. Effective weapons do not have to be exotic, however. The conventional arsenals of the major military powers contain plenty of weapons for the terrorist which do not saddle him with the technical or political burdens inherent in the use of nuclear, chemical, or biological weapons.
One such conventional weapon is the Soviet-built SA-7 Grail surface-to-air missile. The Grail’s launcher tube, which is about the size of a World War II bazooka, fires a missile which guides on the infrared radiation from aircraft engines. It is considered comparable to the U. S.-built Redeye missile which is about four feet long and which can fly at supersonic speeds for a considerable distance in pursuit of a low-flying airplane.
The simplicity and lightweight ruggedness of this sort of battlefield guided
were
required to throw up a special secuti cordon around airports in Brussels a(1 London. The Grail attack never marer‘ alized, but the security measures ne ^ ^ sary to protect against it illustrated t1 type of response required to coun a threat posed by a small groUP people equipped with a very small- effective, weapon.
neady
3babl)'
Wi[b
ments are gaining support daily.
weapon (BGW) make it a prime candidate for deployment with the armed forces of the Soviet Union in a variety of applications. It can be lugged by foot soldiers, mounted on vehicles, or carried on board naval combatants. The technology involved is simple enough to lend itself to mass production.
One reason for heavy Soviet investment in the Grail is that it is a combat- tested system. Use of the Grail against U. S. aircraft in Vietnam was first reported in the spring of 1972. It downed several aircraft at that time and seriously disrupted reconnaissance and helicopter operations, close air support missions, airborne artillery spotting, and other low altitude aviation operations.
U. S. countermeasures, most notably the use of hot flares to mislead the missile’s infrared guidance system, held the casualty rate down but also provided the users of the Grail with a laboratory situation in which to test improvements. The October 1973 Arab-Israeli War offered yet another opportunity to test modifications to the system. As a result, if a Grail operater is linked by today’s improved battlefield communications to one of the many miniaturized radar systems in production, he can be ready for an enemy aircraft before it even comes into view.
The successful record of the Grail has created a demand for the antiaircraft missile in traditionally Soviet-supplied nations and some "neutral” nations.
Several countries already have the Grail system, and as the number of countries increases so do the chances that the link will be created in the chain which will lead to terrorist possession of the deadly missile.
From its Soviet origin, the missile might proceed by any number of circuitous routes on its way to a terrorist organization. The missile might begin as part of an arms shipment to a Soviet- supplied nation such as Syria. Syria, like several of its Arab allies, arms and supports the Palestine Liberation Organization (PLO). This "group” includes several factions, each with varying degrees of loyalty to the central command and differing concepts of the most effective means of obtaining Palestinian goals. It is not too difficult to imagine the possibilities by which a radical faction such as the Black September might obtain weapons from more conservative groups in the PLO by gift, theft, defection of personnel, or sheer mismanagement.
Another possible pipeline exists in that governments which already support terrorist groups might pass the effective missiles on directly. The Qadhafi regime in Libya, recently the recipient of large quantities of Soviet military hardware, has been suspected as the source of Grail shipments to terrorists on at least two occasions.
In the first case, Italian police apprehended five young Arabs who had
rented an apartment in the seaport a of Ostia, near Rome. The apartmen t mi four miles from Leonardo da Vinci port and directly underneath the tra pattern for the North-South run^'0 Cached in their apartment were Grail launchers and a supply of ndssl The Italian press reported that the t rorists were only hours away fr0IT1 planned attack on a commercial This demonstration of the reality the Grail threat led to a dramatic tea tion by Western European government when they were informed that Gr ^ had been shipped to terrorists m
Different activist groups in every part of the world would proL like to acquire weapons like the G whether they planned to employ or not. Groups in Ireland, Quebec'’ Black Africa, Asia, and even the Unite States have resorted, for political rea sons, to tactics which emphasize qul spectacular actions. Spectacular atta have become recognized as imp°rta facets of numerous successful tevo ^ tions or "wars of national liberatin'1. The embryonic revolutionary can 1° to the histories of Israel, CypruSj. Mozambique, Vietnam, and a host other countries to see places where tet rorism helped spawn either a con'e(1 tional war, or a political victory without large-scale military action. .
With the respect generated by cbeir successes, terrorist and guerilla money, influential support, and a feefin? of growing power, the terrorists :in^ their new weapons could be very mu in evidence in the coming months an years.
Editor’s Note: The views expressed art those of the author and do not necessttd) represent the position of the Department °J Defense or the U. S. Government.
tal ar^' m ^/°r^ War II hair-raising Cs shark attacks on survivors of sea asters began to filter back from those 0 lived to tell them. The effect on °rale was serious. Men who could face tile fire with courage became deeply a|. tUrhed by thoughts of being eaten tan^ ^ s^ar^s- -Airmen became reluc- to fly over shark-infested waters. a result, Dr. Harold J. Coolidge of e Office of Strategic Services began Vest'gating the feasibility of develop-
fofi, *
U. S.
s — ^ringer, hered
:rn'cal. Black nigrosine dye was added provide the visual reassurance of Seeing tjje chemiCal spread out in the ater and to provide a concealment . ct°r similar to that provided by the lflk of octopus, squid, and sea hare.
In 1943, a small research team at the 'aval Research Laboratory, which had previously developed the yellow fluores- ^ent Sea Marker dye, was tasked to help evelop the final product. In tests on
a shark repellent. In March 1942, °wing Dr. Coolidge’s initiative, the Navy officially requested research j. development of a shark repellent t0rn the Committee on Medical Re- ffi^h wartime Office of Scien-
c Research and Development.
The initial experiments at the Woods le Oceanographic Institution imme- 'ately ran into difficulties. All the obvi- °Us chemicals failed to prevent sharks r°m attacking the bait. Then Stewart the senior investigator, remem- an interesting fact from his shark shing days in Florida: a dead shark left rotting on a hook drove every other ark out of the fishing area. Because ^°Pper sulphate had previously been Ur|d to have some repellent quality and decomposed shark flesh fluids were Ur>d to contain large quantities of acet*c acid, it was decided to test the repellent effects of the copper ion in ^Ornbination with the acetate ion in the
rrn of copper acetate, a colorless chei • to
large dangerous sharks the copper acetate nigrosine dye combination appeared to be a success. Thus, "Shark Chaser” was born.
The addition of the now familiar plastic packets of Shark Chaser to all life jackets and life rafts had an enormous psychological benefit. However, 30 years of experience and additional tests have shown that copper acetate combined with nigrosine dye is far from being the ultimate in passive defense against sharks. In shark pens at the Lerner Marine Laboratory, Bimini, Bahamas, when each component of Shark Chaser was used separately, captive sharks of six different dangerous species approached the lure through a cloud of copper acetate. The nigrosine dye, however, repelled nearly all the sharks except the nurse shark. In open sea tests Shark Chaser was relatively effective in protecting baited hooks except against black tip sharks. But an actively feeding shark which was striking at anything even ate the open packet of Shark
Chaser. This shark, however, did spit out the packet almost immediately.
The inadequacies of Shark Chaser, coupled with the Navy’s interest in developing improved protection measures against shark attacks as naval operations requiring men in the sea have increased, has led to the present importance of the role of the Office of Naval Research (ONR) in sponsoring shark research.
A super white shark was built for the movie "Jaws, ” but sharks with its dimensions have been caught.
How serious is the shark problem? The records show that of the approximately 250 species of sharks only about 35 are potentially dangerous to man and only about ten of these are proven man-eaters, or more accurately, man- maulers. In fact, sharks as man-eaters may be overrated. Few victims have been eaten alive in the strictest sense of the term. In this regard, Dr. H. David Baldridge, Jr., formerly a U. S. Navy captain with the Naval Aerospace Medical Center, Pensacola, and now a senior research associate at the Mote Marine Laboratory in Sarasota, Florida, is con-
is a
of a much-touted "bubble curtain
vinced from his studies that defensive or just plain testy aggression plays a bigger part in shark attacks on humans than the feeding urge. As he points out, if sharks in coastal waters fed upon people by choice in preference to their natural food, the incidence of shark attacks would be far greater than 100 cases reported throughout the world each year. And of the 100 cases, only about half are fatal. By comparison more than three times as many people die in the United States alone from bee stings or lightning.
So why the great concern about sharks? Primarily because the shark hazard has implications that transcend the damage done to one victim. Attacks on military personnel create morale problems of such proportions that during World War II probably more servicemen drowned from panic at the sight of a shark fin than from shark attack. Furthermore, the Navy’s interest is considerably broader now and involves more than protecting survivors of a sea disaster. The scope of the Navy’s present interest includes the protection of its underwater swimmers, certain types of experimental and operational equipment (for example, the buoyancy equipment used to float recoverable missile nose cones), naval recreational and training beaches, and civilian populations in areas under the Navy’s administrative control.
In the past, many naval operations involving gear recovery and other underwater projects have been curtailed or abandoned because of the aggressive behavior of sharks. Recent studies have shown that some sharks are capable of biting through ropes and cables of substantial size. This capability has resulted in the loss of expensive oceanographic instrumentation when sharks severed the supporting cables. The search continues for better shark deterrents than now exist—deterrents which will protect both people and equipment.
Shark countermeasure research efforts moved slowly after World War II until 1958 when the American Institute of Biological Sciences (AIBS) and Tulane University, with the support of ONR and the Navy Bureau of Aeronautics, sponsored a conference in New Orleans on "Basic Research Approaches to the Development of Shark Repellents.” Two days of discussion quickly revealed that there was a challenging need for more information about the biology and behavior of sharks before more adequate deterrents could be devised.
To meet this challenge, AIBS set up the Shark Research Panel under the direction of Dr. Perry W. Gilbert, Professor of Neurobiology and Behavior at Cornell University and, now, also Director of the Mote Marine Laboratory at Sarasota. This development was followed by the establishment of the Shark Attack File (SAF). SAF has become the most complete historical record of worldwide shark attacks and is now maintained at the Mote Marine Laboratory.
The first report of the Shark Research Panel was published in I960. By 1963, Navy-sponsored research and studies of shark attacks provided enough new information to enable Dr. Gilbert to prepare his often referenced "Advice to Those Who Frequent, or Find Themselves in, Shark Infested Waters” which appeared in a panel report: Sharks and Survival. In 1967 the panel issued another volume of reports also under the editorship of Dr. Gilbert: Sharks, Skates and Rays.
At various times since 1958, ONR, through its Oceanic Biology Program, has sponsored research at 14 universities and research institutions. In addition, a great deal of related research in oceanic biology has been conducted at numerous other institutions. Thus, ONR has played a key role in supporting studies that are important not only to the Navy, but also for increasing the fundamental knowledge of oceanic biology and ecology.
Fundamental to the search for shark deterrents is information about the mechanisms that guide a shark to its prey. Although the shark has a very small brain it has an elaborate sensory apparatus. This includes not only the more familiar eye, ear, and nose receptors, but also more esoteric receptors for the detection of low frequency vibrations outside the usual audible range, such as pressure changes and small electrical impulses of biological origin. The visual apparatus was studied extensively at the University of Miami, the Plymouth Laboratory, Scripps Institution of Oceanography, and Cornell University. At the Lerner Marine Laboratory electroencephalography was employed to
increase knowledge of olfaction in sharks. ,
Much of this shark and shark-relate
research has not come easily or cheap r It is important in evaluating anti-sha devices to test them against several mem bers of a number of species. The testing
good example why this redundancy ** required. When this device was teste against 12 tiger sharks, 11 swam t>ac and forth through the curtain at ’ but the 12th was deterred. Complete? erroneous results would have been o tained had only the 12th shark been used in the tests.
Adequate holding facilities for ntifl1 bers of large, dangerous sharks are e* pensive to construct and maintain. M present such facilities exist at only about a half-dozen laboratories in the won • In the United States there are only three- the Mote Marine Laboratory, the Ur" versify of Hawaii, and the Institute 0 Marine Science at the University 0 Miami. The Lerner Marine Laboratory’ operated by the American Museum 0 Natural History of New York, has ex cellent facilities. Of these facilit*65’ those at Miami have fallen into disuse and those at Bimini may be forced t0 close because of increased costs and m adequate funding.
|
At the Mote Marine Laboratory, Dr' Baldridge, building on the previous work of Dr. Gilbert and the Shark search Panel, has made a computer assisted analysis of data from 1,165 case histories in the Shark Attack File. ’The results were published in a 31 October 1973 report submitted by the Mote Laboratory to Oceanic Biology Programs
° °NR: Shark Attacks Against Man— P/ogram of Data Reduction and Analysis.
■ while the numbers of applicable cases 1^ t'le Shark Attack File may still be too . t0 permit the isolation of really ^gnificant statistical correlations, Dr.
a dridgg prodUCed a work of great j^erest and practical value to those who nc, swim, or dive in the sea, or who ^"ght someday find themselves inadVertently in the shark-infested water.
contrast to the basic research p'onsored under the Oceanic Biology r°grams of ONR most of the applied Search and development of the actual rdware for shark countermeasures has en carried out by the Naval Undersea er>ter, San Diego (formerly called the aval Undersea Research and Develop- ^ent Center and before that the Naval j. n<Jersea Warfare Center). The search r new devices to aid in both the pas- SlVc and active defense against sharks has tUrned up several inventions that show Particular promise. One is the Navy’s J°hnson Shark Screen. This is a plastic ag with an inflatable rim in which a SUfvivor can float with his shape and 'Movements concealed, while any blood 0r other odor-producing body products are kept isolated from the open water. Another Undersea Center develop- is the C02 Shark Dart, a sort of ^uper hypodermic needle. The incentive 0t this device developed from studies which showed that the hydrostatic bal- *nce maintained by large sharks is suf- Clently sensitive to provide a firm screntific basis for the development of lriti'Shark weapons which would upset ^is balance by the injection of gas into che body cavity of the shark. A shark as no air bladder with which to vary lts buoyancy and must, therefore, keep Roving unless it lies on the bottom, when killed, it sinks. What keeps the sbark’s buoyancy (hydrostatic balance) Within controllable limits as it grows in Sl2e and weight is an increasingly large storage of low density oils in a very large liver.
Tests of the Shark Dart were some- tlfnes spectacular. When high pressure C°2 is injected anywhere into the abdominal cavity not only is the hydrostatic balance upset, but there is instant Eternal disruption of the "free floating” 0rgans, often resulting in forcing the Mark’s stomach out its mouth. The
Shark Dart (also known as a gas gun) is now produced commercially in five versions by Farallon Industries.
The same basic principle of hydrostatic balance lies behind another concept for an anti-shark device that has not yet been developed. Stewart Springer, instrumental in the development of Shark Chaser, told of "planking a shark.” The idea was to attach a piece of buoyant wood to a shark so that it swam very erratically and was rendered helpless. It was subsequently suggested that the same effect could be obtained by sticking or firing a lance to which was attached a small drogue parachute into a shark.
A self-contained electrical device known as the Shark Shield has been used successfully for more than four years by shrimp trawlers to discourage sharks from attacking the cod end of the trawl. The Shark Shield is powered by rechargeable batteries and delivers, through a pair of electrodes, a square wave, 120- volt DC electric pulse with a frequency of one to two per second and a duration of 60 ms. This device was effective in repelling four species of adult sharks known to be dangerous to man in tests at the Mote Marine Laboratory.
Another electric anti-shark weapon has been tested by Dr. H. D. Baldridge and the Mote Marine Laboratory in collaboration with Dr. Scott Johnson of the Undersea Center. It is a self-contained electric dart capable of instantly immobilizing a large shark by a flow of current from the dart’s imbedded tip through a complex of pathways in the shark’s body to the surrounding sea water and, hence, to the external electrode of the dart. Thus far, this device has not been uniformly effective against all species of sharks.
The Lerner and Mote Marine laboratories are testing the use of dolphins
A Navy diver equipped with the C02 Shark Dart (upper left) attracts a six-and-a-half foot blue shark. The photo (immediately above) demonstrates the effect of a Shark Dart hit—the stomach has been forced out of the shark’s mouth and keeps the shark afloat until it dies.
and porpoises as anti-shark weapons. Experience with intelligent and trainable dolphins led scientists to seriously consider the possibilities that such animals could be trained to ward off sharks in areas where divers were engaged in underwater operations. In 1971, a male bottlenosed dolphin was caught in the Gulf of Mexico and placed in a tank at the Mote Marine Laboratory. This dolphin, named "Simo” (the Greek word for snub-nosed), was used initially in tests that showed that dolphins and sharks are not natural enemies. Subsequently, experimenters were able to condition Simo to forcefully butt sharks on signal and to harass and drive large sharks from his pool on command. Only a bull shark seemed to faze him. However, a shortage of funds interrupted this program and Simo was released.
The search goes on. The shark problem has not been eliminated, but advances have been made since the Navy actively began to promote research on sharks and shark countermeasures in 1958.
Omega: A Status Report
By Captain Charles W. Koburger, Jr.,
U. S. Coast Guard Reserve, Omega Navigation System Operations Detail (ONSOD)
The U. S. Navy, in cooperation with the U. S. Coast Guard and participating foreign countries, is in process of constructing and operating the worldwide very low frequency Omega navigation system. The Navy has provided the electronic equipment for the program, while a Coast Guard detail coordinates the overall operation of the system. Most of the individual stations overseas are operated by the host countries. Although the system has been under development for more than two decades and some navigators, at least, have had contact with Omega, apparently not everyone really understands it.
The Omega radio navigation system, like most navigation systems, has a military heritage. (Both Loran and Decca, for instance, were developed during World War II.) When the initial work on Omega began it was envisioned as the only technically possible solution for obtaining a reasonably priced global-coverage navigation system. The concept was, and continues to be, based on the utilization of principles similar to those employed in Loran and Decca, with the purpose of extending the coverage achieved by these systems by operating in the very low frequency (VLF) range of the radio spectrum.
Twenty years ago no one foresaw that superior alternative navigational techniques would soon emerge. Inertial navigation, for example, is more advantageous for military use because it is completely self-contained on board an equipped platform. It is, therefore, less vulnerable to attempts to neutralize or jam it than a ground-based radio navigation system such as Omega. The advent of the space age may have opened the way to satellite navigation systems, but Omega remains a reliable, simple, and cheap alternative.
In light of current trends, it seems safe to predict that within a decade, the great bulk of Omega users will be merchant shipping, fishing vessels, the airlines, and the scientific community. The military services will likely continue to use Omega as a backup system. In a non-hostile environment, Omega is too handy and economical an aid to ignore.
Omega is an all-weather navigational aid designed to give worldwide position fixes (generally accurate to within 1 to 2 miles) adequate for most marine and air navigation. In theory, Omega can provide worldwide coverage with six Omega stations (OMSTAs), but for geographical and technical reasons, eight are needed. (See Figure 1.)
During the research and development phase a prototype system, operating at 1 kw, was tested. The last 1 kw prototype, U. S.-contracted OMSTA Trinidad is due to be phased out and replaced by a standard station in Liberia.
Each standard Omega transmitting station is equipped with a timing an control set, a transmitter, an antenna tuning set, the antenna (tower or valley span) and ground subsystem, a remote monitor, a data link tying the monitor
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Lines of position cover the typical Omega navigational chart.
669
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t^e control system, and an emergency pow« generator.
/ ®mega utilizes VLF constant wave a , ^ s'gnals between 10 and 14 kHz, atlc* set aside by international agree- ^er>t in 1947 for navigation aids. This st MnCy ranSe uniquely suited for e radio transmission over long
Paths.
T
0 use the Omega system, with the prcal marine receiver costing $5,000 to >000 (airborne units cost approxi- satc'y $50,000), it ordinarily is neces- *7 to have Omega overprinted charts— shIleS wifh hyperbolic lines
diff^'Hg tPie exPecred basic zero phase erence from various pairs of stations; and 274 c ■ 1 ■ ■
tak series propagation correction
es> giving predicted seasonal and ^Urnal corrections for the charts. Both produced by the Defense Mapping gency’s Hydrographic Center. (The e expensive airborne receivers make fecial charts unnecessary, reading out rectly in geographic coordinates.)
£ ^ position fix is normally obtained 0tn Omega by comparing or measur- j.®. tple "phase” (i.e. relative time) erence for synchronous signals reed from various stations, usually en ln pa;rs Any tw0 convenient sta- rjs can be used; there are no mas- q 'Save relationships between stations. .°°d reception and large crossing an- s are the key factors. Each pair of gnals gives one line of position. Three th Crent Pa‘rs °f stations, i.e. at least . ee stations, giving three lines of posi- , n> are therefore normally required.
. 0re can be used if desired. The read- nSs thus achieved are then corrected ^cording to the published tables to . °'v for predictable aberrations of the Slgr>al in specific areas and at specific tlrTles. (The computerized Omega re- Ccjver handles this process automati- v ) The accuracy of the fix depends °n the timing precision of the transputers, the degree to which the signals ev'ate from their expected velocity en r°ute, and the precision of the receiving eSu'pment.
/transmitter timing is kept exact to ^'rhin two to three-millionths of a sec- °n<i, but even this small margin permits P°sition-fix errors of about 200 yards.
npredictable deviations in the signal jplocity cause additional errors of several Uridred yards even in good conditions.
Therefore, even assuming the use of a very accurate receiver, the signals themselves can contain substantial errors.
Each of the eight standard stations in the system transmits, or will transmit, three standard navigation frequencies (10.2, 11.3, and 13.6 kHz) and has been assigned two "unique” frequencies. (These unique frequencies were intended originally for station identification, although they may be used for navigation and other purposes, such as international time, time interval, and frequency standardization signals. At present, only the two Omega stations operated by the U. S. Coast Guard regularly transmit unique frequencies. The controlling international agreements must be modified before the transmission of unique frequencies by foreign stations can be included as a definite part of the transmission format.) Each signal is transmitted for approximately one second. The signal cycle, with time spacing, has a total of eight "slots” available for signals. The cycle repeats itself every ten seconds (continuously) with each station picking up the sequence in turn, in what is sometimes called "time-sharing.” (See Figure 2.)
The principal navigation difficulty in the use of Omega is "lane ambiguity.” This stems from the fact that signal readings repeat themselves every so often. Any two stations’ signals are thus, at intervals, the same, establishing "lanes.” Normal receiver read-out is in lanes and hundredth of lane. The Omega signals provide lines of position relative to the boundaries of a lane, but do not identify the specific lane. The navigator must establish his position by other means with sufficient accuracy so
.672 i MANSEL ISLAND" -667 - -660
.
U. S. NAVAL OCEANOGRAPHIC OFFICE
that he knows what Omega lane he is in. It is sometimes possible to start from a known fixed position, then keep counting the lanes crossed; this counting is achieved automatically on some receivers.
Lane identification is otherwise not usually difficult to determine if the individual lanes are wide enough. The three standard Omega navigation frequencies were chosen to provide a spread along virtually the entire width of the internationally-assigned radio navigation frequency band. As presently used, they provide a maximum lane width of 72 miles. Using some or all of the unique frequencies in combination with the standard frequencies can offer the navigator a greater number of the more desirable wider lanes. The combined signal is also less subject to propagation anomalies than a single one by itself.
■
Propagation disturbances are another recognized problem for Omega. These disturbances cannot be eliminated; we must learn to live with them. These signal anomalies come from a variety of electro-magnetic sources: sudden ionospheric disturbances (SIDs); Polar Cap disturbances (also called "absorption”) (PCDs or PCAs); and other, so far unidentified, atmospheric noises (UANs). On the average, there are six to eight SIDs a month, of relatively short duration (20 minutes), four to five PCAs a year, of longer duration (two to three days), and only occasional UANs. Normally these disturbances do not have equally adverse effects upon all Omega signals available at any one location. Redundancy in the number of signals available is, therefore, an important countermeasure to this problem.
Figure 2. Omega Stations and Their Signal Formats
Station | Station Letter Designation | 1 | Broadcast Phases (1 2 3 | -8) and\Frequencies Transmitted/kHz] 4 5 6 7 8 | |||||
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| i_____ "I |
NORWAY | A | | 10.2 | 1 1 13.6 | | I 11.3 | | I 12-1 | | I 12.1 | | I 12.1 | | 112.35 | | [12.351 |
TRINIDAD* | B | I - | 1 1 10.2 | | I 13.6 | | I 11-3 | | I - I | m | I - I |
|
HAWAII | C | 111.55 | I 111.55 | | I 10.2 | | | 13.6 | | I 11-3 | | I 11.8 | | I 11.8 | | frCfl |
MHDTU |
|
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| nsi __ |
DAKOTA | D | | 13.1 | | 112.85 | | 112.85 | | I 10.2 | | I 13.6 | | I 11.3 | | I 13.1 | | |
LA REUNION | E | | 12.3 | 1 1 12-3 | | 112.05 | | 112.05 | | I 10.2 | | | 13.6 | | I 11-3 | | fr2i3 l |
ARGENTINA | F | | 12.9 | 1 1 12.9 | | I 12-9 | | 113.15 | | 113.15 | | I 10.2 | | I 13.6 | | rrm ____ |
AUSTRALIA | G | | 11.3 | o CO | I 13.0 | | I 13.0 | | 112-75 | | 112.75 | | I 10.2 | | |7a61 |
JAPAN | H | | 13.6 | I I 11.3 | | I 12.8 | | I 12.8 | | I 12.8 | | 113.05 | | 113.05 | | pia21 |
* Prototype, temporary substitute for Liberia.
of
igation skills while perfecting his use
When propagation disturbances are discovered, either on Omega monitor sets or from other sources, the Omega Navigation System Operations Detail (ONSOD), Washington, D.C., initiates Notices to Mariners, through the facilities of the Defense Mapping Agency, and issues Notices to Airmen. ONSOD also sends messages to a special address indicator group announcing the anomalies.
By the end of this fiscal year three more standard stations (Argentina, La Reunion, and Liberia) will join the five operational Omega stations (four standard and one prototype). The goal for Omega is to provide a signal-noise ratio of not less than — 20 decibels in a 100 hertz bandwidth, worldwide, and to provide enough signals so that at least three, and usually four, lines of position can be plotted from good Omega signals anywhere on the globe, at any given time. The absence of an OMSTA in the Tasman Sea area (tentatively Australia) will mean that coverage in the Southwest Pacific and Indian Ocean will continue to have deficiencies. Alternative sites for this eighth standard station are being considered and this gap will be filled as soon as possible.
The operational reliability of the Omega stations fully on the air is about 99% (excluding scheduled downtime) with mean time between failure (MTBF) equal to, or greater than, 1,000 hours, and mean time to repair (MTTR) equal to, or less than, 30 minutes. Downtime must still be scheduled from time to time for special engineering modifications, although these are becoming less frequent. Eventually, system-wide reliability should be considerably better than 95%.
Omega need not be, nor should it now be, the sole navigational technique used. It is entirely up to the resourcefulness and ingenuity of the navigator to how best use and incorporate Omega in his navigation plan. For example, a navigator’s daily routine might consist of the following:
► Round of stars at morning twilig^1
► A morning sunline crossed with one or more Omega lines
► A (noon meridian altitude of the sun crossed with one or more Omega lineS
► An afternoon sunline crossed with an Omega line
► Evening twilight round of stars
► At night, periodic Omega fixes based on three or more LOPs
Such a routine would permit the navigator to maintain his celestial nav
Omega. Of more possible significance a useful fix can be provided each time that observations are made and positions are plotted.
For the seaman or airman, Omega >s essentially a high seas, or en route, navigation system. Its accuracy will be quite sufficient for these civil shipping and aircraft operations. When a vessel is within 200 miles of most ports or when an aircraft is within a similar range of land, or an airport, other, more precise navigation aids are available for use.