Analysis of Airphoto Linear Pattern zn EasternMassachusetts

ALBERT E. PRESSMAN*

Office of A erospace ResearchA ir Force Cambridge Research, Lab.

Bedford, krass.

where exposed even the most competent bed­rock is in many places deeply gouged andHuted.

INTRODUCTION

AN AIRPHOTO linear as herein described isany narrow, fairly continuous lineation

of natural origin which is discernible understereoscopic analysis of aerial photography.In this area, which includes portions ofClinton, Boylston, Berlin, Northboro, andMarlborough Townships, Massachusetts, themajori ty of these features was expressedprimarily as tonal lineations in the soil orvegetative cover, and less often as alignedtopographic features such as straigh t streamsegments or lake banks. Occasionally com­binations of the above were noted, e.g., astraight stream segment perfectly alignedwith a lineation in the adjacent vegetation.The average length of the lineal'S in this areais approximately t of a mile, and all areshorter than t of a mile.

The object of this study is to determine1) if a relationship exists between the air­photo linear pattern and the surficial or bed­rock geological conditions of the area, and2) if the recording of total number of lineal'Sin relation to orientation will yield similarresults when compared with total length oflineal'S in relation to orientation. To accom­plish this the length, orientation and locationof 1,234linears were measured.

PREPARATION 0" AIRPHOTOLINEAR MAP

To prepare the Airphoto Linear Map(Figure 2) the entire area was analyzedstereoscopically, and lineal'S were delineatedon transparen t overlays attached to everysecond print. Using these delineated photo­graphs! a staple photomosaic was assem bled(Figure 3). Because each overlay is attachedat only one end of a print it is possible tojoi n them so that none of the interpretedinformation is hidden by side or forwardlap. Due to the inherent distortions in asingle exposure the photographs do notmatch perfectly along common edges. Tocorrect partially for the larger discrepanciesfound at the overlap zones, an editing stagewas included prior to final drafting. When­ever two or more seemingly individuallinears(mapped along overlap zones) were actuallya single feature duplicated by photo mis­match, a final linear was annotated whichrepresented the mean location and orienta­tion of the origi nals. Because none were dis­placed over a few hundred feet, or rotatedmore than a couple of degrees, these minor

GEOLOGICAL SETTING inaccuracies should not affect the results of

The area lies in the east-central portion of the study.2Massachusetts, approximately 30 mi west of The final map (Figure 2) is a tracing of theBoston and 10 mi northeast of \i\Torcester annotated mosaic and covers approximatelyFigure (1). As mapped by Emerson (1917) it 40 sq mi.is underlain generally by a northeast trending ANALYSIS OF AIRPI:IOTO LINEAR PATTERNcomplex of gneisses and schists of moderatelyhigh metamorphic grade. These rocks have The histogram of ail-photo linear orienta-been tightl~ folded and intruded by granite tion in relation to per cent of total numberand pegmatite (Skehan, personal communica- (Figure 4) is distinctly peaked and reflects a

tion). 1 Aerial photography was obtained from theThe terrain has been greatly modified by U.S.D.A. at contact scale of 1:20,000. The prints

the Pleistocene ice advance. The region is were supplied through the courtesy of Boston Col-almost entirely veneered by glacial drift the le~e, Dept. of Geology. . O' .

d. tt I b d ' L111ears were grouped 111 10 onentatlon seg-

ralnage pa ern las een eranged and ments.

_ * The author is a geologist an~ since August 1961 served as a contractor representative to the AirJ'orce Cambndge Research Labs. HIs home address is 1062 Belmont St., Watertown 72, Mass.

193

194 PI-IOTOGRAMMETRIC ENGINEERING

FIG.!. Jndex map showing location of study area (A), and Hudson andMaynard Quadrangles (B), Massachusetts.

non-random distri bution of orien tation. Max­imum occurrence is in the N 11°-20° W seg­ment (19%) with lows in the northeast andnorthwest directions (Table 1).

The histogram of per cent of total length ofairphoto lineal's in relation to orientation(Figure 5) is in very close agreement with(Figure 4) (number vs. orientation) showingthat there is no preferred orientation withlength of linear.

a) RELATJONSHIP TO BEDROCK GEOLOGY

Various workers in this interest area havenoted the presence of similar linear features

seen under stereoscopic examination of air­photos. Occassionally attempts have beenmade to relate their pattern to the geologicsetting in order to determine their origin.Lattman refers to si milar features as fracturetraces (1958, p. 569) and a parallelism of"fracture trace," and joint orientations in theAllegheny Plateau, Pennsylvania has beenshown successfully (Lattman and Nickelsen,1958).

Blanchet terms these features fractures andhas reported (1957) on the detection of aburied reef in Alberta by the presence of asurface "fracture" anomaly discern able on

FIG. 2. Airphoto linear map of study area, Massachusetts.

ANALYSIS OF AIRPHOTO LINEAR PATTERN

FIG. 3. Staple photomosaic of study area, Massachusetts.

195

FIG. 4. Per cent of total number of airphotolineal'S in relation to orientation.

aerial photographs. rt was assumed that up­ward propagation of fractures to the surfacethrough bedrock, unconsolidated soils, andglacial overburden does occur.

In the study area underlain by crystallinerocks there is no related parallelism betweensubsurface fracturing (joints and/or faults)and bearing of airphoto lineal'S. A preliminarystudy of data from a detailed subsurface map­ping program along an 8 mile tunnel trendingnorthwestward through the center of (hearea reveals that primary fracturing orienta­tion is N 60° W, and secondary direction is

0: 20...III

'"~ 16..J

'"t-o 12t-...o"ifl eCIl0:

'" 4...z:::;

60 40 20 20 40 60 EAST

approximately N 45° W (Skehan, personalcOll1m unication). The bed rock stri ke is gener­ally N 20°-50° E which also indicates nocorrespondence with the airphoto linear pat­tern.

b) RELATlONSHll' TO SURFICIAL GEOLOGY

Figure 6 compares per cent of total num­I,cr of glacial striations with orientation.These features which were mapped in theadjacent Hudson and Maynard quadranglesby Hansen (1956) (see Figure 1) representthe direction of the latest advance of contin­cntal glaciation. Of 112 striations found onbedrock outcrops, a peak of 44 per cent trendN 1°_10° W, 92 per cent trend N 20° 'vV toN 9° E, and all are distriuuted between N 30°Wand N 20° E.

The close agreement between t.he directionof the glacial striae and the orien tation of theairphoto lineal'S proves almost conclusivelythat the lineal'S discerned on these aerialphotographs are indeed indications of thelatest ice flow direction (compare Figures4 and 5 with Figure 6).

Because the length of the Ii nears average

196 PHOTOGRAMMETRIC ENGINEERING

TABLE 1

ORIENTATION OF AIR PHOTO LlNEARS AND GLACIAL STRIATIONS, EAST-CENTRAL MASSACHUSETTS

A irphoto Linears Glacial Striae

Total % TotatTotat % Total Total % TotalOrientation Length

No. No. (mi) Length No. No.

N 90 0 -81 0 W 32 2.59 3.64 2.30N 80 0-71 0 \V 47 3.80 5.48 3.46

70 0-61 0 W 27 2.18 2.68 1. 70N 60 0 -51 0 W 9 .73 .99 .62~ 50 0-41 0 W 7 .57 1.00 .63N 40 0-31 0 W 45 3.65 5.96 3.77N 300-21 0 W 105 8.51 13.33 8.43 4 3.57N 20 0 _11 0 W 235 J9.03 29.19 18.43 21 18.75N 100 _ JO W 209 16.94 28.40 17.96 49 43.75N 00 _ 90 E 173 14.02 22.20 14.04 33 29.46N 100 -19 0 E 143 11.59 19.32 12.21 5 4.46N 20 0-29 0 E 69 5.60 9.77 6.17N 300-39 0 E 32 2.60 3.31 2.10N 40 0 -49 0 E 17 1.38 2.11 1.33N 500 -59 0 E 22 1. 79 2.53 1.60N 600 -690 E 20 1.62 2.35 1.49N 700 -79 0 E 15 1.21 1.88 1.19N 800 -89 0 E 27 2.19 4.05 2.56

Total 1,234 100 157 100 112 100

675 ft they obviously are not photographicimages of striations. However, they probablydo reflect geomorphic features which aregenetically si milar. These features are qui tesubtle on the photographs and may be diffi­cult to observe in the field Figure (7).

The Airphoto Linear Density Map (FigureSa) consists of contours drawn around zonesof high linear density. Its comparison withFigure Sb shows a definite relationship withthe land lise pattern. The wooded zones,usually on topographic highs, are almostalways rcprcsented by high linear densitieswhile along c1earcd areas (mostly farms)airphoto linears arc scarce. At present eitheror both of the following reasons are bclicvedresponsiblc for this relationship.

1. Many airphoto linears in this area werc

mapped on the basis of lineations in thenatural vegetative pattern. Therefore, wherethe land has been cleared a major clue is mis­SIng.

2. An examination of the surficial geologymap of nearby similar areas (Hudson, May­nard Quads., Hansen, 1956) (see Figure 1)shows a relationship between type of exposedunconsolidated deposits and topography. Theareas of low relief are identified almost alwaysby stratified drift deposited by glacial melt­water, while the topographic highs arecovered by ground moraine composed ofheterogeneous deposi ts of rock fragmen ts.The reworking of the vallcy materials bymeltwatcr may have disrupted the linearpattern still evident along the higher eleva­tions.

20 40 60 EAST

TOTAL 112

:I: 20 50l-e>z... 16 40..J

..J

'".. ZI- 0 300 12I- ;:.. ..0 ii:

"II- 20'"on ..0

0: 4 10• "I...Z

..J0

60 40 20 20 40 60 EAST WEST 60 40 20

FIG. 5. Pcr cen t of total length of airphoto linearsin relation to orientation.

FIG. 6. Per cent of total number of glacialstriations in relation to orientation.

ANALYSIS OF AIRPHOTO LINEAR PATTERN 197

FIG. 7. Various lineations seen on aerial photography, (A) airphoto linear, (B) lineation in vegeta­tion reflecting bedrock strike, (C) lineation due to cultural activity. In this study only features of typeA were mapped. Location shown on Figure 3.

CONCLUSIONS

1. A definite parallel relationship in orien­tation exists between the airphoto linears inthe study area and the glacial striae on bed­rock outcrops in an adjoining but partiallyoverlapping area. No such similar relation­ship exists between the linears and bedrockstrike or subsurface fractures (joints and/orfaults). This indicates that the linears arerelated genetically to the glacial striae andreflect the latest movement of the glacier.

2. The plotting of total nltmber of linearsin relation to orientation and total length oflinears in relation to orientation shows thatin the study area there is no preferred orienta­tion of length of linears.

3. The topographic highs usually coveredby heterogeneous ground moraine and usu-

ally wooded are characterized by high densi­ties of airphoto linears. Linears rarely occur

,in the lower areas which are mostly veneeredby stratified glacial meltwater deposits andcleared by cultural activity.

RECOMME~DATlONS

Future research in the interpretation ofairphoto linear patterns may require thatonly one of the parameters be determined,i.e., total length or total number of linears inrelation to orientation. This would save con­siderable effort. In studies such as this onewhere all measurements ,,·ere made manuallytotal number \\·ould require less time. How­ever, semi-automatic equipment has beenbuilt \\·hich is capable of determining onlytotal length of lines in relation to orientation.

198 PHOTOGRAMMETRIC ENGINEERING

N

1TWO MILES

FIG. 8. (A) Airphoto linear density map; Contours enclose areas oflinear concentration. (B) Photomosaic of area.

If available, this equipment would reduce thetime required for surveys of this type by morethan SO per cent.

Field" investigations should be undertakento locate and determine the nature of featuresreflected as airphoto linears. These featuresmay be quite subtle, presumably due to 1)aligned minor contrasts in soil compositionand 2) narrow, fairly straight changes invegetation height, density or type.

Systematic soil sampling and testing todetermine grain size, gradation, moisture con­tent, mineralogic content and color, as well asvegetation studies including tree counts,trunk diameter measuremen ts, stand heights,and variations in vegetal types may be neces­sary to establish definitely the surface loca­tion of these airphoto linears.

Locating airphoto linears in the field will begreatly facilitated if undertaken at the sametime of year at which the photography was

exposed. During July-August the surfaceconditions will most closely resemble theseaerial photographs of the study area.

LlTERATURE CITED

Blanchet, P. H., 1957, "Development of FractureAnalysis as Exploration Method," Bull. A mer.Assoc. Petrol. Ceol., Vol. 41, No.8, pp. 1748­1759.

Emerson, B. K., 1917, "Geology of Massachusettsand Rhode Island," U. S. Ceol. Surv. Bull. No.597, 289 p.

Hansen, W. R., 1957, "Geology and Mineral Re­sources of the Hudson and Maynard Quad­rangles Massach usetts," U. S. Ceol. Surv. Bull.No. 1038, 104 p.

LaUman, L. H., 1958, "Technique of MappingGeologic Fracture Traces and Lineamen ts onAerial Photographs," PHOTOGRAMMETRIC EXGI­NEERING, Vol. XXIV, pp. 568-576.

---, and Nickelsen, R. P., 1958, "PhotogeologicFracture Trace Mapping in AppalachianPlateau," Bull. Amer. Assoc. Petrol. Ceol., \'01.42, No.9, pp. 2238-2245.