402 PHOTOGRAMMETRIC ENGINEERING

Objectives of charting operation·s theworld over are very similar. Dissimilaritiesare chiefly in the methods and equipmentused, and in the physical conditions underwhich the actual surveying is carried on.At ,this Conference we look forward tohearing of the experience of the UnitedStates hydrographers in their charting ofnorthern seas and harbors.

To sum up: The concept of all theCanadian Arctic waters being charted onan adequate scale, is one devou tly to bewished for, but one exceedingly difficult of

accomplishment. The character of thecoast, the severe climatic conditions, thestrong tidal currents and dangers to sur­veying vessels from heavy ice and un­known reefs, all militate against rapidprogress in nautical charting. Yet, it isthese very reasons that add up to thenecessity, and indeed the urgency, of hy­drographic operations. As long as de­fence, economic and scientific developmentcontinue, the concept of adequatelycharted northern waters is not likely to bealtered.

HYDROGRAPHIC SURVEYING IN THE ARCTIC

Lt. Comdr. T. K. Treadwell, Plans and Policy Division, U. S. NavyHydrographic Office, Washington, D. C.

Hydrographic surveying may be roughlydefined as the gathering of all necessaryfield information for the production of nau­tical charts. Due to the nature of the me­dium, hydrography in arctic and sub­arctic regions does not differ in principlefrom hydrography in temperate or tropicaldimates. If the water is not solidly frozen,the same methods of depth determinationare used no matter where surveys aremade. In the even t that the water surfaceis completely solid, special techniques maybe necessary such as breaking the ice,drilling holes to reach the water, or .takingsoundings through the ice itself. So manypractical difficulties arise in making hydro­graphic surveys through a solid ice coverthat it is almost never done on a largescale, but is limited to small areas or spotdepth determinations made in connectionwith other scientific observations.

Even at the best, however, hydrographyin the north presents some unique prob­lems for men and materials. Though thesurface may not be frozen solidly, it israrely ice-free, and the floating ice is anever-present and ever-changing hazard tothe ships and boats taking soundings. Re­inforcement of hulls, and modification ofsome engineering details is necessary, orelse a certain calculated risk of damagemust be accepted. Survey instrumentsmust be specially lubricated and carefullyhandled to operate satisfactorily. Theclimate affects operations too by decreasedvisibility and poor working conditionsbrought on by snow, fog, rain and highwinds. Much of the position fixing for

sounding operations ,is now done elec­tronically, and is therefore independen t ofvisibility. It would be foolhardy, howeverto operate ships in ice-filled waters wherethe rocks and shoals are at best only im­perfectly known.

An additional point is the comparativeinhospitality and remoteness of the north.In warmer, more populated regions, aninsured man ashore, a survey party in dis­tress, or a grounded boat is almost alwayswithin range of friendly assistance fromthe local people. In the arctic, where thethe nearest settlement may be hundreds ofmiles away, there is little possibility ofgetting local assistance or of buying emer­gency supplies from the nearest store. Thedetached survey party is on its own andmust make do with what it has.

The purely psychological effect of thecold is considerable. There is the naturalfeeling in the back of one's mind that extra·caution is necessary; that a mistake injudgment or a' freak of nature may leadto discomfort, injury, or death. This feelingis bound to impede the progress of anoperation which is exploratory by nature,and in which a good measure of calculatedrisk is ordinarily accepted. Added to thisawareness of unusual hazard is the purelyphysical discomfort of low temperatures.Heavy protective clothing is almost anecessity for survival, although it greatlylessens personal efficiency. A balance mustusually be struck between discomfort andthe freedom of movement necessary tocarry out the survey work. Even at best,proportionately longer rest periods are

PANEL ON ARCTIC MAPPING, 403

needed to thaw numbed fingers and relaxthe chilled body.

The avy Hydrographic Office realizesthe difficulties of working in the arctic,and ordinarily employs a full survey groupfor a job. The standard group consists ofone large, tender-type survey ship, andtwo smaller ships. These carry four to sixsounding launches, amphibious trucks,numerous small boats ·.and landing craft,assorted shore vehicles, and one or morehelicopters. Seven hydrographic officer spe­cialists, four civilian engineers, and ten totwenty enlisted CB surveyors are assignedto the technical work. These are in additionto the several hundred line officers andmen necessary to carry out the routinework of ship operation, maintenance, andsupport of tpe survey. Unskilled and semi­skilled workmen for boat crews and con­struction parties are drawn as needed fromthe ship's company.

Each such survey group carries sufficientsurvey equipment and supplies for an ex­tensive operation. The group is able to gointo an area and make a complete chartingsurvey. The preliminary work includes tak­ing the necessary astronomical observa­tions for position and azimuth, laying outa precise base-line, observing a second­order triangulation network, and carryingout essential field photography and pho­togrammetry. Thousands of miles ofsounding lines are then run by ships andboats, using visual or electronic control,and the accessory tide, current and ocean­ographic observations are taken. The re­sults are processed as the work proceeds,and if desired, a five-color field nauticalchart can be printed on board ship for im­mediate use.

, In the preparatory phase of the survey,the first technical difficulty to be encoun­tered is that of obtaining the astronomicalposition and azimuth, due to the shortenedperiods of darkness and the erratic recep­tion of radio time signals. This has beenpartially bypassed in some cases by the

procedure of observing a series of accuratelines of position on the sun, using a theo­dolite. Magnetic observations for variationare difficult to obtain, due to the decreasedhorizontal magnetic component. Markingof permanen t geodetic poin ts presen ts aproblem when they must be located on ice,snow or permafrost.

In the sounding operations, the hazardsof ice and low visibility have already beenmentioned. Carrying out a predeterminedsounding pattern is further complicated bythe fact that in high latitudes the mag­netic compass, and to a lesser exten( thegyro compass, become sluggish and er­ratic, making it difficult to hold a straightcourse. The actual soundings are taken bystandard Navy recording fathometers,supplemented by hand lead soundings andwire dragging as necessary. The rocky na­ture of the bottom makes pinnacles andabrupt shoals common, and particular caremust be exercised to insure that no dangerto navigation is overlooked. The inshoresoundings are taken by the launches, usingthree-point visual sextant fixes on shoreobjects. The offshore hydrography is de­veloped by the larger ships, using elec­tronic control. Radar beacons were for­merly used, bu t are gradually being re­placed by such systems as Shoran, EPI,and Lorac. Unfortunately, the perform­ance of electroni 'positioning equipmen tin the arctic tends to be erratic and gen­erally subnormal which somewhat lessensits utility.

To sum up, hydrography in the arcticis often difficult and hazardous. The chal­lenges presented by the environment aredisturbing principally because they are un­familiar to the newcomer. Equally difficultproblems, however, confront the hydrogra­'pher in all other areas. With careful prep­aration, technical ability, common sense,and experience, these uniquely arcticproblems can be dealt with effectively, andone of the last fran tiers of tne world canbe accurately charted.