392 PHOTOGRAMMETRIC ENGINEERING

form of the F-13 appeared on the scene.Crews received more training and the re­sults improved proportionately. There stillwas a long way to go howeyer. With thearrival of Shoran, many felt that tre­mendous progress had been made in theright direction.

It is evident that we are moving towardthe goal outlined by Col. Sewell when hesaid "Precision automatic flying. would behighly desirable, since automatic equip­ment is generally more sensitive and reli­able than human reaction."

The straight line computer with the air­borne Shoran sets keep the planes on astraight line in this difficult navigationalarea.

Shoran provides the most economical,accurate and rapid means of providingaerial photographs for mapping purposestoday. To conduct a successful operationrequires tons of equipmen t oi all kinds,cargo aircraft, helicopters, photo-mappingplanes and outstanding electronic spe­cialists. This is why we do not see manyof these units in existence today. But in thelong run it is cheaper in cost since thenumber of re-f1ights are reduced, and theinsurance on the chances of carrying outthe missions correctly the first time are in­creased 100 per cent.

The specifications for our mapping re­quire staying within a 53 to 65 per centforward overlap, the desired being 60 percent and an average of not greater than56 per cent; a sidelap of between 15 and30 per cent; a tilt of not greater than 3degrees in any case and an average of notexceeding one degree; and a crab of notover 5 degrees. With such specificationsand considering the limited mapping ex­perience of the crews, it is a wonder that

any of the photography was considered ac­ceptable.

Automatic equipment is one answer;another is intensive training of the crews.The photo sohool at Lowry Field is con­sidering expanding its present course tosatisfy this requiremen t.

With regard to those involved in amapping program I mentioned that theymust understand the need for the maps.They must also have an individual interestin the program.

A specialized mapping Squadron is oncemore being formed. The recent conceptthat a Reconnaissance. Unit could do thiswork as part of its training is changing. Asurvey of personnel recently taken in oneof our major commands indicated a con­siderable interest in joining the unit. Theobjective is to select the personnel withthe most experience for this unit. We areheaded in the righ t direction in this re­spect, for personnel with little or no inter­est in this work will result in considerableunnecessary cost in both time and money.

There are also new types of automaticequipment to be provided these unitseventually. This will permit staying withinour specifications easily and require onlythe surveillance of the crews for it t6 func­tion properly. We should soon see the timewhen aircraft, operating automatically andunmanned, will be dispatched on a map­ping mission and return to a predesignatedbase.

Perhaps we shall see the day whennuclear powered aircraft capable of stayinj!aloft for days and limited only by theendurance of its crew, will search outareas of good weather and thereby achievethe now very ambitious goal "complete ac­curate mapping of the earth's surface."

CONTROL FOR ARCTIC MAPPING

C. H. Ney, Assistant Dominion Geodesist, Department of Mines andTechnical Surveys, Ottawa, Canada

SYNOPSIS

Possible methods are classified under twoheadings-astronomic and electronic.

Astronomic Methods:

(a) Precise astronomical telescope(b) Astrolabe(c) Zenith cameraInherent errors of the methods

Electronic Methods:

(a) Shoran(b) Decca(c) RaydistUse of methods and inherent errors

Vertical Control

Barometric and trigonometric levelling sup­plemented by radar altimetry

PANEL ON ARCTIC MAPPING 393

Organization and Transportation:

Main and satellite depotsTransportation: helicopter, dog team, aero­

planes, and freight canoesPortable radio transceivers a prime necessity

for integration of work.

For the establishment of mapping con­trol in the Arctic, a number of possiblemethods suggest themselves. In general,they may be considered under three classi­fications-astronomic, electronic and di­rect mcasuremen t.

PRECISE ASTRONOMICAL METHOD

The precise astronomical method, usinga broken-axis type astronomical· telescopeoriented in the meridian plane, will giverelatively high accuracy in sub-polarareas. The instrumental equipment weigh­ing about 600 pounds may be set up readyfor work in less than two hours time. Aposition determination accurate to 30 or40 feet, astronomically, may be securedby a three hours' observation. One hourwill usually suffice to determine the posi­tion with an accuracy of 75 to 100 feet. Inhigh latitudes where the atmosphere is freefrom smoke and dust, star observationalwork may be carried on during mid­morning or mid-afternoon periods ofbright sunlight. With instruments havingobjective lenses of 50 or 60 mm., first,second and third magnitude stars may beused for daylight observation.

THE ASTROLABE METHOD

The astrolabe method applied to pre­cision theodolites has been used extensivelyin the Canadian northland. Four or fivestars are observed in each quadran t at afixed altitude (usually 45 degrees or 60degrees). The instrumental equipment,which weighs about 200 pounds, may beset up ready for work in less than onehour. To determine a position accurateto 150 or 200 feet, astronomically, four orfive hours observing is required. To ensurean accuracy of 100 feet, observationsshould be made over two nights.

Since 1929, the Geodetic Survey ofCanada and to a lesser extent the Topo­graphical Survey, have established some1,500 astronomic control stations in north­ern Canada. About 380 of these points arelocated in the Arctic or sub-Arctic areasnorth of the tree line.

ZENITH CAMERA METHOD

During the 8-mon ths period of eachyear when stars are visible to the nakedeye, the zenith-camera photographic meth­od might be useful. By this method, severalphotographs are taken of the stars closeto the zenith at the point of observation.The Greenwich time of each exposure isalso recorded by photographing the faceof the chronometer at the instant of platef'xposure. After processing, the rectangularcoordinates of the stars' images are scaledoff the photographic plates.

From these data, the geographical posi­tion of the camera station may be deduced.I t is claimed by the proponen ts of thezenith-camera method that an accuracycomparable to that of the astrolabe maybe secured in a short period of time. Duringthe long summer period in the Arctic whenstars are not visible to the naked eye, thezenith-camera could not be used. In addi­tion, the processing of the plates in thefield would involve considerable difficultyattended by possible breakage. Up to thepresent time, the portable field Zenithcamera has not been used in Canada.

As is generally known, all astronomicalmethods of position determination are sub­ject to inherent errors due to unknown de­viations of the vertical, which, in Canada,are found to have an average value of 300feet. For this reason, astronomical fixa­tions are suitable only for small-scale map­ping where the anomalies due to the devi­ations of the vertical are obscured by thesmallness of the map scale.

CONTROL BY TRIANGULATION AND ROUTE

TRAVERSES

Considerable control comprising tertiarytriangulation and route traverses has beenestablished in northwestern areas by theTopographical Survey and the Army Sur­vey Establishment of the Department ofNational Defence. Some of the route tra­verses have involved win ter tractor opera­tions in the barren-land area west ofHudson Bay.

Among other projects in' this categoryare the following:

(a) Winter traverse from Fort Nelsonto Fort Simpson.

(b) Tertiary triangulation from the141st meridian eastward to the MackenzieRiver basin.

(c) Winter traverse along the 60th

394 PHOTOGRAMMETRIC ENGINEERING

parallel of latitude westward from theMackenzie Highway to the northwest cor­ner of the Province of Alberta and thencesoutherly to Hay Lake.

SHORAN ELECTRONIC METHOD

Shoran trilateration provides control ofexcellent ultimate value-comparable al­most to second-order triangulation, andfree from the effects of deviation of thevertical. With the co-operation of theRoyal Canadian Air Force, the ationalResearch Council, and the MeteorologicalService of the Department of Transport,the Central Canada Shoran net has beenextended since 1948 from the vicinity ofthe 49th parallel of latitude northerly andnorthwesterly as far as the Arctic coast.A few hundred miles to the south of thenorthern extremity, this net has. been ex­tended in 1952 eastward towards HudsonStrait. At the close of the 1952 season, linemeasurement operations have been fin­ished as far as the westerly limits of BaffinIsland. Altogether 230 lines have beenmeasured in the network in which theaverage and maximum lengths of line are210 and 362 miles respectively. The recon­naissance and station preparation work hasbeen completed for several hundred milesboth northward and southward fromHudson Strait. During the 1953 season itis hoped that the southerly arm will beextended to a junction with the Gulf of St.Lawrence primary triangulation net.

However, in an area such as the Arcticwhere transportation involves major dif­ficulties, the inherent disadvantages ofShoran should be carefully considered.These unfavorable features include thenecessity of repeated visits to each stationsite, the transportation of heavy and bulkyequipment, the employment of numerouspersonnel, and the comparatively longtime necessary to complete a station.Yesterday; Major Thompson presented apaper dealing with the application ofShoran-controlled photography to Cana­dian mapping.

DECCA-ELECTRONIC METHOD

Decca is a radio system of posltlOn­fixing in which three transmitting stations,at known points on the earth's surface,lay down two intersecting patterns of hy­perbolic-shaped position lines. These pat­terns are printed on topographical maps orcharts, or on a basic grid for use in un-

mapped areas. The position-fixing instru­men t is a portable radio receiver tuned tothe transmitters and driving a pair of"Decometer" indicators which displaycontinuously the numerical values of thetwo position lines on which the receiver islocated. The desired geographical positionis.given by the point of intersection of thepair of correspondingly-numbered positionlines on the chart. The process of positionfixing is therefore simply the matter ofreading two dials and plotting the inter­section of the two position lines.

The degree of accuracy obtainable fromDecca fixations at the present stage of de­velopment is not too well known. Com­paratiye tests over ranges covered by geo­detic tria,ngulation should prove of greatinterest.

FIXATION METHODS RECOMMENDED

In the northern part of the Arcti'carchipelago, there remain vast areas withIi ttle or no con tro!'

In regions where only small-scale map­ping is required, precise or second-orderastronomy is recommended as the mostpractical method of establishing horizontalcontro!' For areas such as harbor ap­proaches, anchorages and airports wherelarge-scale mapping is planned, Deccashould be investigated. Should it appear tobe unsatisfactory, the alternative would bethe adoption of route traverses or tertiarytriangulation. .

VERTICAL CONTROL

Vertical control has been carried bytrigonometric levelling through a sec­ondary triangulation net extending fromthe Gulf of St. Lawrence to Ungava Bay.In the winter of 1950-51 precise levels wereextended along the winter tractor roadfrom Fort Nelson, B. c., to the 60thp'arallel of latitude

In the.more remote Arctic areas, verticalcontrol could be best established by baro­metric and trigonometric levelling and ra­dar altimetry. At the completion of thehorizon tal con trol work, aeroplanesequipped with radar altimeters would beflown between control stations or alongroute traverses, so that profiles of thelines might be accurately determined. AsMr. Waugh discusses the use of the radaraltimeter in his paper, the subject will notbe elaborated here.

PANEL ON ARCTIC MAPPING 395

ORGANIZATION AND TRANSPORTATION

The general plan for the establish men tof control would involve the placing andretention of survey units at main or satel­lite depots throughout the entire year. Inthis way, the work could be carried onduring the favorable periods of both thewinter and summer seasons. In the extremenorth, the weather station at Resolute onCornwallis Island could be used as themain depot. Farther south, CambridgeBay, Frobisher or Coral Harbor could beused for the same purpose.

In the areas where astronomical meth­ods are to be used, it is proposed that eachdepot should be manned by two or threesurvey units, each consisting of an ob­server, a recorder and two labor assistants,all under the supervision of the depot chief.

The survey units would proceed outradially from each depot to establish thenecessary control stations. During themonths of March, April, May, October,November and December, helicopter ordog team transportation supplemented byaeroplane drops of food and fuel shouldprove highly satisfactory. A 10-dog sledteam will haul a load of 1,600 to 1,800pounds under normal winter' conditions.During the winter months, aerial co-op­eration would be more or less limited to thebright periods of the moon. Due to theexcessive cold no work would be plannedfor January or February.

During July, August and Septemberconsiderable progress could be made using

helicopter, aeroplane, or canoe-plane-droptransportation.

In coastal areas, the use of 22 foot freightcanoes equipped with outboard motors isrecommended. These craft will carry i tonwith ample free board; they weather sur­prisingly high seas and have the addedadvantage of lightness and mability. Incase of theatening danger from ice orstorm, both the cargoes and canoes may beremoved from the water to the relativesafety of an ice pan or on the shore.Geodetic survey parties have travelledhundreds of miles along the Hudson Baycoasts with this type of craft which hasproved to be preferable to a schooner orwhale boat.

RADIO COMMUNICATION

Good radio communication between thedepot and its field survey units is a primenecessity. The modern type of small radiotransceivers (G.S.ll or P.F.1) used forsome years by the Geodetic Survey ofCanada, are quite satisfactory. They arepowered by dry batteries and operate oneither continuous wave or phone with platevoltages varying from 90 to 200 volts.

In general, the problems of transporta­tion are much more complex than thoseconnected with the technical end of theproject. However, if the new high-ceiling,freight-carrying type of helicopters weremade available for the work, no serious'difficulty would be expected to attend theestablishment of mapping control.

HORIZONTAL AND VERTICAL CONTROL FOR ARCTIC MAPPING

Comdr. Hubert A. Paton, Chief, Baltimore Photogrammetric Office,U. S. Coast & Geodetic Survey

SYNOPSIS

A detailed survey of the Arctic Coast ofAlaska by the U. S. Coast and Geodetic Surveyhas been in progress since 1945. New methodsof transportation of supplies and personnelwere employed. An arc of second order triangu­lation was extended along the shore for a dis­tance of 680 miles and astronomic stations wereestablished and base lines were measured. Ele­vations referred to sea level datum were placedon triangulation stations. Extreme weather con­tions required the development of new tech­niques -in surveying methods. New types ofclothing were tested and new living proceduresdevised.

For eighty years the U. S. Coast and

Geodetic Survey has been sending fieldparties to Alaska, bu toniy in recen t yearshas it been feasible to send them into theArctic regions. The Bureau did cooperatein the early part of this century with theAlaskan Boundary Commission in estab­lishing an arc of triangulation along the.141st meridian; this was completed in1912. In 1945 a party was ordered to pro­ceed to Point Barrow to begin a detailedsurvey of the Arctic coast in order thathydrographic charts could be published.These charts require accurate topographicand hydrographic surveys, and to controlthem it was necessary to extend an arc of