suit in great savings of time and money.There is, however, one very important

phase t of highway location and designwhere the photogrammetric methods andthe electronic computing machines cannotsupply information. This is in the realm ofsoil surveys, materials location, and generalsite and route evaluation based on the inter­play of the natural environmental factors.Here also the airphotos can be used tosave time and money in the planning, de­sign, and construction phases.

By the time-worn procedures of the soilauger and samples taken at evenly spacedintervals along the route, how much timewould be required to sample soils alongthis 41,000 miles of highway? In additionmany miles of preliminary routes wouldhave to be investigated before the locationof the 41,000 miles could be finally estab­lished. Also during this time these same

Photographic Interpretation­Its Significance in theHighway Program*

JAMES H. Me LERRAN, Ass't. Chief,Photographic Interpretation Research Branch,

Snow Ice and Permafrost Research Establishment,Corps of Engineers, U. S. Army, Wilmette, Illinois

ABSTRACT: The impact of the new highway program will require develop­ment and utilizatwn of time-saving methods to obtain information re­quired for planning, location, design, and construction.

The use of airphoto interpretation to evaluate soil and materials isa proven method that will save much tzme. Illustrations show the applica­tion of the technique to specific engineering uses, such as soil surveys andmaterial prospecting. The use of airphoto interpretation and carefullyplanned field work should go hand in hand.

There are several ways to develop utilization of information gainedby this technique. Many photogrammetric engineering firms could de­velop a staff capable of supplying a "package deal" to the highwaydepartments. Highway departments should develop and encourage a sta.!!of trained personnel. Cooperative research programs with colleges coulddevelop the technique for a geographic area, and aid in training per­sonnel. In addition, qualified consultants could be contracted to supplythe information desired.

BEFORE the American Public and thehighway engineers lies an almost stag­

gering public works program. The impactof this 41,000 mile highway program, calledthe greatest construction job conceived bymen, will create a terrific strain on an al­ready too small engineering force. Thatthis is realized by those in the highwayfield is indicated by the recent emphasis ontime-saving methods in many publicationsand at many highway conferences. At therecent ARBA conference in Chicago twoseparate sessions were devoted to devel­opment in the use of two of these time­saving devices-photogrammetry and elec­tronic computers. These time-saving de­vices will relieve the designers of manytasks connected with topography, cross­sections, earthwork computations, andmany other tasks normally performed bytechnicians, engineering aides, and juniorengineers. I t has been well demon-strated that the use of photogrammetry t I am responsible for the italicizing in thisand electronic computing devices can re- paper.-EOITOR.

* Presented at the 23rd Annual Meeting of the Society, Shoreham Hotel, Washington, D. C.March 3, 1957. This paper is a part of the Panel on Photogrammetry in the New Federal HighwayProgram.

755

756 PHOTOGRAMMETRIC ENGINEERING

highway departments would be workingon many other miles of highway not in­cluded in this inter-state program. It canbe appreciated that this would be a stag­gering, if not an impossible job in the timerequired to accommodate the demands ofthe rapid growth of traffic. The drivingpublic will not be satisfied to wait for thisdevelopment to take place by time-con­suming procedures. The need is now! Dif­ferent procedures and new methods areneeded, must be found and used.

The use of airphoto interpretation tech­niques to evaluate soil and materialsconditions is not new, but has been de­veloped over a period of 15 to 20 years.This has been largely on a research basis,but a few progressive highway organiza­tions and contractors have used suchmethods for several years with excellentresults. In the light of this, it is appallingto note in a recent survey of time-savingmethods that only eighteen state highwaydepartments gave positive statements thatthey were employing airphoto interpretationmethods for soil surveys. Five other states in­dicated that they were experimenting withits use. (11)

The purpose of this paper is to discussphoto interpretation and how it can beused in this highway program.

USES

Airphoto interpretation will save timeand promote better highways in severalways. Several of the uses of the techniqueare:

1. Preliminary interpretation of soils andother natural environmental factorsduring the planning, reconnaissancesurvey and preliminary location surveystages.

2. Engineering soils maps along proposedlocations.

3. Location of construction materials closeto the route.

4. Determination of potential engineeringproblems, such as hard rock cuts andlandslides.

To obtain the full benefits of airphotointerpretation, it should be started withthe initial planning and reconnaissancesurvey stages. There are several environ­mental factors, determinable by interpreta­tion, that control the economics of a location.Four of these environmental factors arediscussed below.

GRADE AND ALIGNMENT

In many instances the topographicfeatures will exert predominant controlover the location. The use of airphotos,under stereoscopic study, will aid inevaluating a location that will provide themost desirable features. Figure 1 illustratesan area where the topography verystrongly controls location. The rivershown in the photograph has cut a ser­pentine path more than 1,000 feet deepin hard basalt rock. The slopes are steepand the highway must cut into the edge ofthe valley to maintain an easy grade. Air­photo interpretation can determine wherethe roadway must be cut out of hardbasalt rock and where it will cross de­posits of coarse talus. Unstable or problemareas can be located readily. Here thechoice exists between the two sides of theriver and both possibilities can be evalu­ated.

SOIL CONDITIONS

Photographic interpretation providesthe means for rapid evaluation of soilconditions along possible routes during thelocation stage. All too often the soil condi­tions have not been investigated untilafter the location has been determined.Adjacent soil areas may have wide differ­ences that affect the design thickness ofthe pavement or the construction proce­dures. It is important to utilize the soilsthat provide the best results for the leastexpenditure. Figure 2 shows a typicalexample where the evaluation can bedetermined by interpretation of the soilconditions as pictured on the aerial photo­graph.

One soil area is composed of glacial till,which often contains seepage areas alongslopes. Adjacent is a terrace composed ofgravels with good internal drainage (Noteworkings along face). The remaining areais composed of recent alluvium with poordrainage and poor strength characteristics.The alluvial soil will require considerablepavement thickness and, due to its char­acteristics and low position, can be workedonly during dry periods.

The till in this area has good strengthcharacteristics but contains enough poormaterials to prevent construction workexcept during dry periods. The terrace hasthe advantage of providing the higheststrength foundation and also has theadvantage of being workable during wet

PHOTOGRAPHIC INTERPRETATION 757

FIG. 1. An area where the topography strongly controls highway location. Bedrock conditionsand type can be analyzed to estimate design and construction problems.

periods, which is important as this areais located in a region where there are manyrainy days throughout the year. Delaysdue to wet soils can be costly and thisterrace will aid in reducing these costs ifthe route is located upon it rather thanthe adjacent soil areas. A similar evalua­tion of the soil conditions along a routecan aid a contractor in programming hiswork. Thus, an airphoto evaluation canmean savings for the contractor as well asfor those concerned with design and loca­tion.

FIG. 2. The airphoto provides a means forreadily evaluating soil conditions. The gravelterrace in this area provides a good area forhighway location or a source of constructionmaterial to be used elsewhere.

MATERIALS LOCATION

It is important that highways be locatedto take advantage of available construc­tion materials when possible. The cost ofconstruction increases rapidly when con­struction materials must be hauled greatdistances. The terrace shown in Figure 2,which. was readily identified on the air­photo, would provide a valuable sourceof base course material for any nearbyhighway.

CULTURAL FEATURES

Many miles of the highways in this newprogram will be located by the influence ofcultural features on right-of-way costs.Where possible, the highway will have tobe located to avoid going through the mostexpensive land in vast urban and industrialareas. The airphoto can aid in carefullyselecting a route that takes advantage ofstrips of lower cost property through theseareas. The problem exists even in ruralareas where farmers are already concernedabout the wide strips of valuable agricul­tural land being consumed for our com­plex transportation network. By the air­photo alone, locations can be determinedthat take advantage of the least produc­tive areas when other factors do not con­trol. Figure 3 shows an area with twodistinct cultural patterns. One side of the

758 PHOTOGRAMMETRIC ENGINEERING

river has an intensive agricultural pattern,whereas the other side shows no agricultureand, therefore, lower land values.

All these factors can be evaluated andan analysis made for a route location con­sidering them from the advantage of acomprehensive viewpoint that the airphotogives. The airphoto records the naturalenvironment and the interpretation pro­vides an analysis of their effect upon thehighway location and design.

FIG. 3. An area with two distinct culturalpatterns. The upper portion has an intensiveagricultural pattern, whereas that below theriver shows no agriculture and, therefore, lowerright-of-way costs.

TECHNIQUES

The principle of airphoto interpretationhas been explained many times and will

be mentioned only briefly here.* Thebasic principle is that materialsunder similartopographic and climatic conditwns willexhibit similar airphoto patterns, and unlikematerials will create different patterns.

The pattern can be described as thecombination of certain recognizable ele­ments as recorded upon the airphoto. Theseelements that singly or together form asignificant pattern are: landform, drainagesystem, erosion characteristics, photo tones,vegetation, and land use. The basic prin­ciple and the pattern concept are illus­trated in Figure 4. Dissimilar materialsunder similar climatic conditions havegiven the airphotos contrasting patterns.Figure 4a illustrates the airphoto patterndeveloped in areas where flat-lying lime­stone and its residual soil are exposed un­der a semi-humid climate. Here the soils,consisting of plastic clays, will be found tobe six to ten feet deep and only infrequent,shallow rock excavation will be necessaryfor highway construction. Figure 4billustrates another rock type in this area,that of massive sandstone beds. Thetopography consists of flat, blocky uplandareas with steep valley walls. The soils areshallow upon the uplands and highwayconstruction here will require large cutsand fills to obtain good grade and align­ment. Figure 4c illustrates the airphotopattern developed in areas of flat-lying

* Several references in the bibliography ex­plain the principles and the techniques in detail.

(a) (b) (c)

FIG. 4. Three contrasting airphoto patterns in southern Indiana created by different types ofsedimentary rock. (a) The sinkhole pattern identifies residual soils over limestone. (b) Steepescarpments, angularity and blockiness of the pattern identify massive sandstone. (c) Rollingtopography, intricate drainage and erosion pattern indicate residual soils over shales.

PHOTOGRAPHIC INTERPRETATION 759

FIG. 5. An area with a uniform airphoto pat­tern. One sample site is all that is required insuch an area since uniform soil conditions areindicated. The airphoto pattern identifies thematerial as windblown silt.

shales in the same general region. Here thetopography is rolling, and highway con­struction will require frequent cuts throughtroublesome shales.

Rather than explain the step-by-stepprocedure of photo interpretation, thetechnique will be shown by the use ofseveral illustrations. These will illustratethe technique and the significance of air­photo interpretation for the specific ap­plications of soil surveys and materialsprospecting.

SOIL SURVEYS

Airphoto patterns vary from those thatare simple and easily interpreted to thosethat are complex and identifiable only byclose scrutiny. Also there is a difference inuniformity; some soil areas are uniformover large expanses but in other areas soilconditions vary greatly. In an area suchas shown in Figure 5 there is no need toemploy extensive field sampling since thesimple uniform airphoto pattern indicatesuniform soil conditions. Not only will thisobservation save time in field surveys,but it will reduce the number of samplessent to an overloaded soils laboratory.

Figure 6 illustrates an area where theairphoto pattern varies considerably fromone portion to another with irregularboundaries between different soil areas.Within each major soil unit are found de­pression soils and soils developed on highareas. Where the pattern is different, it islogical to expect a different soil condition.Sampling in the field will necessarily bemore extensive than in Figure 5 since soilcharacteristics must be established and the

FIG. 6. An area where the airphoto patternvaries considerably from one part to another.Within major soil type units significant differ­ences also can be noted. Extensive soil samplingwill necessarily be required in such an area, andthe airphoto provides a means of planningwhere sampling should be conducted. Circlesalong a theoretical route indicate where sampleswould probably be required in this area.

boundaries of each soil unit carefullychecked. The airphoto provides a meansof locating the different soil units and theirboundaries. Thus, before going into thefield, the field exploration can be plannedand organized. This can reduce under­sampling an area as well as reducing over­sampling.

Not only can soil units be mapped andan engineering evaluation given, but alsounderlying rock types can be established,as illustrated previously in Figure 4. Alsounstable conditions such as landslidesleave their tell-tale mark upon the air­photo, aiding in avoiding such areas. InFigure 7, the characteristic topography ofa landslide area shows up clearly on theairphoto, indicating an area that shouldbe avoided.

FIG. 7. The characteristic topography of alandslide area shows up clearly on the airphoto,indicating an area that should be avoided.

760 PHOTOGRAMMETRIC ENGINEERING

MATERIALS SURVEY

The location of construction materialssuch as sand, gravel, and quarry rock closeto the site is essential in highway con­struction; these materials are in shortsupply in many areas today. In the past,many sources were located by word ofmouth, and by chance. In today's highwayprogram this method will not suffice. In arecent publication the closing instructionfor materials prospecting was as follows:

"Much walking and hard work are necessaryfor making an intensive materials survey. Aprospector must be alert and efficient and hemust keep on looking for materials with a viewof finding a source just 100 yards beyond wherehe desires to turn around. Instances are onrecord where good material was found just overthe hill from where another prospector gottired and stopped. One should not exchangehard work and walking for the comfort ofriding, if he expects to be a good materialsman." (7)

These were good instructions once upon atime. But now the prospector can exchangeendless walking for a method that doeslocate the material that is "just over thehill" while not leaving the office. The useof airphoto interpretation will reduce muchtime in locating materials where required,and will find many sources that have eludeddiscovery by "hard work and walking." Byphotographic interpretation the search isnot confined to a narrow width as it is onthe ground.

Construction materials are frequentlyhard to find in areas of residual soils under­lain by sandstone or shale, and the searchfor materials in these areas is most im­portant. Figure 8 illustrates an area wherethe major features indicate an area of in-

FIG. 8. A gravel outwash remnant thatclearly shows on the airphoto within an area ofintensely eroded shales. This gravel could be animportant source of construction material.

FIG. 9. An isolated area of limestone withinan area of sandstone and shale mantled byloess.

tensely eroded shales. The bedrock in suchan area would certainly not provide suit­able materials for highway construction.Yet within the area illustrated is a sourceof gravel that is easily identified on theairphoto and would be a very valuable findin this area. Even the thickness of thedeposit, which is a remnant of an oldoutwash plain that mantled the shales,can be estimated.

The location of isolated good bedrockmaterials within an area of generally poormaterials can also be determined fromthe airphoto. This is illustrated in Figure9, where a small area containing the sink­hole pattern, which was shown in Figure4a, indicates an outcrop of limestone. Thearea is otherwise devoid of constructionmaterials as the bedrock is largely sand­stone and shale mantled by loess. Such afind could be very important.

River terraces which are good sources ofsand and gravels are usually sharply de­fined upon the airphoto. Figure 10 show~

terrace remnants standing out in sharpcontrast to the glacial debris surroundingit. Such terraces provide a source that canbe easily and cheaply worked.

How To DEVELOP USE

As pointed out earlier, many highwaydepartments have not taken advantage ofthis reliable and time-saving technique.Why? The answer is largely inertia-thelack of interest in changing from the useof old methods. The time schedule and thework-load will not allow this to continue.Another reason is a lack of adequatelytrained photographic interpreters in theengineering profession; successful inter-

PHOTOGRAPHIC INTERPRETATION 761

FIG. 10. Terraces defined by characteristiclandform and lack of vegetation stand out insharp contrast to the glacial debris surroundingthem. The lack of vegetation indicates rapid in­ternal drainage.

pretation and analysis cannot be obtainedby handing an improperly trained engineera volume of photo-keys and asking him toevaluate soil conditions. Cost certainly isnot a factor, since aerial photography,taken for photogrammetric and planningpurposes, is available on most projectswhere photographic interpretation is neces­ary today. In addition, photography ofadequate scale and quality for interpreta­tion is obtainable at very low cost frommany organizations, such as the Com­modity Stabilization Service, U. S. De­partment of Agriculture.

There are several ways to develop uti­lization of information gained by photo­graphic interpretation of soils and otherenvironmental conditions. Many firms nowsupplying topographic maps made by photo­grammetric methods could develop a staff tosupply an engineering analysis of the en­vironment as part of their job. These con­tracting firms would have to develop astaff adequately trained in engineering andthe processes of geology. Thus, these firmscould supply a "package deal" to thehighway department.

Highway departments should at least de­velop a minimum staff that can analyzeconditions from photographic interpretation.They would derive many benefits if allthose responsible for soil and materialsurveys were able and encouraged to usethe technique.

Where will the highway organizationsfind these men? They should enlist the aidof the colleges and universities. Engineeringanalysis of soils and materials by photo-

graphic interpretation should rate high onthe research plans of these schools; the high­way departments that encourage it withcooperative research grants will obtaingood returns on their investment. Theschools can train students while develop­ing techniques applicable for the type ofsoils and geology found within their region.Much research could be done on thesignificance of certain vegetative patternsin terms of the engineering characteristicsof the materials it often obscures. Thestudents so trained could then be offeredopportunities to join the highway soils andmaterials staff. Once employed, theyshould be encouraged to apply their skillsby assignment to specific projects and notbe used as common technicians. Highwaydepartments also can encourage their pre­sent personnel to take advantage of shortcourses offered and to utilize the techniqueon specific projects.

In addition, the highway departmentscould derive many benefits by contractingfor the services of qualified consultants withinthe field. Many construction contractorshave successfully used this method tolocate adequate materials for constructionnear a job site and have reduced their costsfo r these materials.

SUMMARY

In summary, the present huge highwayprogram will require that old outdated meth­ods be scrapped and time-saving methods besubstituted to keep the program going onschedule and to obtain the most for the dollarspent.

Airphoto interpretation is not new, buthas been developed over a period of 15 to20 years. I t can be and has been used tosuccessfully evaluate the environmentalfactors that control the location and designof our highways. Illustrations have shownthe application of the technique to specificengineering problems, such as soil surveysand materials prospecting. The airphotois a valuable tool, but it is not suggestedthat it supplant all field investigation. Itwill not provide all the answers, but thenneither does the soil auger. The use of air­photo interpretation and carefully plannedfield work should go hand in hand.

There is more than one way to developthe use of these time-saving techniques, buthighway departments should encourageresearch and initiative of their personnel andof engineering schools in their region to de­velop techniques for their area.

762 PHOTOGRAMMETRIC ENGI EERING

BIBLIOGRAPHY

1. Belcher, D. J., "The Engineering Signifi­cance of Soil Patterns," Proceedings of theHighway Research Board, Vol. 23, 1943.

2. Frost, R. E., et al., A Manual on the Air­photo Interpretation of Soils and Rocks forEngineering Purposes, School of Civil Engi­neering and Engineering Mechanics, Pur­due University, Lafayette, Indiana, March1953.

3. Frost, R. E., "Factors Limiting the Use ofAerial Photographs of Soils and Terrain,"PHOTOGRA~fMETRIC ENGINEERING, Vol.XIX, no. 3, June 1953.

4. Frost, R. E., and Woods, K. B., AirphotoPatterns of Soils of the Western UnitedStates, Technical Development Report No.85, (Civil Aeronautics Administration)U. S. Department of Commerce, 1948.

5. Jenkins, D. S., et al., The Origin, Distribu­tion and Airphoto Identification of UnitedStates Soils, Technical Development Re­port No. 52, Civil Aeronautics Administra­tion, U. S. Department of Commerce,Washington, D. c., May 1946. (See Ap­pendix B).

6. Johnstone, J. G., "How Airphoto Inler-

pretation Can Speed Highway Plan­ning and Design," Roads & Streets, Nov.1956.

7. Land, J. L., "Design of Flexible Pavementsin Alabama," Flexible Pavement Design inFour States, Highway Research Board,Bulletin 136, 1956.

8. McLerran, J. H., "Airphoto Interpretationof Soil Conditions," 1954 ProceedingsNorthwest Conference on Road Building,University of Washington, Feb. 1954.

9. Mintzer, O. W., and Frost, R. E., "How toUse Airphotos and Maps for Material Sur­vey," Highway Material Surveys, HighwayResearch Board, Bulletin 62, May 1952.

10. Smith, P. c., "Appraisal of Soil and TerrainConditions for Part of the Natches TraceParkway," Public Roads, Vol. 26, No. 10,Oct. 1951.

11. ---, Time-Saving Methods in HighwayEngineering, Chapter 9, "Soils and Founda­tions," Highway Research Board, May1956.

j OTE: The airphotos used in this paper werephotographed for the Commodity StabilizationService, U. S. Department of Agriculture.

Contractors' Acceptance of MeasurementsMade by Photogrammetric Methods*

R. W. PARKS,

Vice President, Dickerson, Inc.,Monroe, lVorth Carolina

ABSTRACT: 1. Statements made at prior meeting in Atlanta recently,relative to acceptance by Highway Engineers and Contractors.

2. Adoption by engineers dependent on their conclusions of the com­parable accuracy with prevailing methods.

3. Comparatively recent practice of furnishing contractors withplans containing limited information, thus requiring the contractor todo his own quantity take-offs and bidding lump-sum or on a mileage basis.Such a contractor would be equipped to handle the proposed methods ofph%grammetry.

4. The highway departments and manufacturers should providethe advance education of the contracting industry prior to letting cons/ruc­tion con:lracts under these new methods.

T HE science of photogrammetry andelectronic computing on highway work

has not been applied to any projects in thearea in which our company normally

operates. Some use has been made of aerialphotographs in the preliminary stages ofhighway location work in some of thestates. But the preparation of the plans

* Presented at 23rd Annual Meeting of the Society. Hotel Shoreham, Washington, D. c.,March 4, 1957. This paper is a part of the Panel on Photogrammetry in the New Federal HighwayProgram. '