T H E ARCHAEOLOGICAL APPLICATION OF L A R G E SCALE COLOUR AND COLOUR INFRARED AERIAL PHOTOGRAPHY

OVER T H E LOWER WAIPOUA RIVER VALLEY

by Caroline Keen CV- Anthropology Dept., University of Auckland, Private Bag, Auckland 1

A B S T R A C T

A n experiment was carried out over the lower Waipoua River Valley (see Fig. 1) to test the application of colour infrared film in surveying for archaeological features in a varied and densely vegetated landscape. Evidence for extensive prehistoric use of the study area was obtained by taking large scale colour and colour infrared aerial coverage. Colour infrared film was shown to detect features not visible to the human eye from either aerial or ground perspec­tives. The results from this application suggest that agricultural use of the lower river valley area may precede upper river valley stone systems.

I N T R O D U C T I O N Colour Infrared Photography in Archaeology

Colour infrared film has been used in past archaeological investigations to detect areas of concentrated cultural deposits or cultural changes in the en­vironment (Tartaglia 1977). A basic principle when using this technique is the assumption that differential soil compaction, density of chemical composition, and the physical alteration of the surface are the main variables which affect the amount of absorbed and reflected solar radiation and thereby delineate cultural and natural anomalies (Tartaglia 1977 p44).

It is on this assumption and ground survey observation that we can differen­tiate between surface and subsurface features using their spectral appearance. Infrared film will provide additional cultural landscape information that is not visible to the human eye.

The archaeological section of the New Zealand Forest Service (Auckland) provided financial backing for the acquisition of large scale colour and colour infrared photographs over portions of the Waipoua Valley. Archaeological in­vestigations in the Waipoua region to date have been heavily concentrated on the upper regions of the valley and the Kawerua coastal area, within N.Z.F.S. jurisdiction (Charters 1982, Coster 1979, 1983, Lawlor 1984, Moore 1984, Pap-worth 1980, Pierce 1982, Taylor in prep., Taylor and Sutton 1985). Although not visible through 'dense' secondary vegetation canopy cover, the effective rear­rangement of natural stone distributions in mounds, terraces, boundary markers, has left an obvious and widespread mark on the upper Waipoua River valley landscape. Where the stone distribution diminishes, an alluvial valley floor replaces a steep sided almost floorless valley. This combined with dense vegetation cover makes archaeological features less obvious for archaeological

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I N D I G E N O U S F O R E S T

Fig. 1. Upper and lower regions of the Waipoua River valley.

Fig. 2. Vegetation cover in the lower Waipoua River Valley.

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recording and analysis during ground survey (See Fig. 2). This study, unlike others before it, was conducted on privately owned land

(where less is known about the archaeological landscape). This paper aims to test the value of aerial photographic techniques for proving the potential for archaeological research in previously (politically and logistically) inaccessible areas.

M E T H O D S

Data Acquisition The photographs were taken at the end of summer in A p r i l , 1986. We

departed from North Shore Aero Club, Dairy Flat, in a high wing Cessna 172, at 9a.m. Two Hasselblad (500 E L / M ) cameras, with 80mm focal lengths, were mounted in a dual camera perspex frame which was fitted to the camera hatch in the base of the aircraft fuselage. One camera was fitted with Kodak E P D 475, 200 A S A , E6 colour slide film, and the other with Kodak 2443 colour infrared A E I 10FS 40. A yellow (blue absorbing) filter was fitted over the lens of the camera containing the colour infrared film. The area covered by both colour and colour infrared film is shown in Figure 1. The runs used here were 12/4-12/12 colour; and 19/3-19/20; 20/1-20/3 colour infrared. These had good forward overlap allowing three dimensional inspection of the area. Each negative was enlarged to a 200mm print (3.6 times enlargement). The average scale of each photo was 1:3143.

Data Analysis The photographs were analysed using a lupe, light table and stereoscope.

Two maps were produced — one of the colour run, and one of the corres­ponding colour infrared run over the same area — showing potential cultural vegetation patterns in the area.

Any features with a cultural appearance were assigned a location by placing a clear cm grid overlay over the photo with the point of origin (00) at the bot­tom left hand corner. Photos were oriented with the river mouth to the west. With each photo location a description of the feature was given. This documented elsewhere at great length (Keen, n.d.pp 41-48, 52-54). Each feature was described according to its tone, texture, size, shape, and location with respect to environmental classes, and association with other cultural features, and a preliminary explanation of the feature type.

RESULTS

Approximately 50 features indicating prehistoric human land use in the lower river valley region were visible on the colour photos (see Fig. 1). Most features occur on the northern side of the Waipoua River where less post-contact land modifications have occurred and where the vegetation is regenerating uninter-

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Fig. 3. NZFS 13, Flight A263. Archaeological features from CIR.

rupted by current land use in the valley. In effect this allows the natural vegeta­tion to act clearly as a surrogate for surface and subsurface features.

A l l features detected on the colour photos were clearly visible on the C I R photos. Twenty five further features were identified on the colour infrared photographs (see Fig. 3). Over fifty percent improvement in information con­tent was therefore provided by the infrared coverage.

Colour infrared film enhanced information available by increasing both depth perception and tonal contrasts of vegetation in the valley. A ground truth assess­ment was done on specific types of spectral signatures on the southern bank. This was to assess the validity of interpretations made from tonal and textural spectral signatures derived from the photos. A correlation was found between vegetation height and features topographically visible on the surface, the vegeta­tion tonal variation and non-appearance of features, on the surface. The hypothesis here is that most features represented by tonal contrasts possessed little surface topography and therefore were assumed to be subsurface in origin. Excavation would further confirm the existence of subsurface features in the lower Waipoua river valley, however excavation was not permitted at the time

Fig. 4. NZFS 13, Flight A263, Archaeological features from colour photos.

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of ground assessment. The fifty percent increase in information available on colour infrared film

in itself is an advance in archaeological survey. The additional information has clarified the features seen on colour photographs by making pattern, and spatial distribution of sites more complete. Patterns which were difficult to interpret from colour photographs as they appeared to be incomplete or isolated, were often found on colour infrared photos to be longer and many were found to connect, providing a more complete feature signature. Colour infrared has revealed three enclosed (circular or rectangular) areas evenly spaced along the northern bank which seem to be central to the lineal systems, (i.e. possible drains) previously located in the study, with lines leading away from them to swamps or the river. These were perhaps settlements or garden centres which required more intense drainage.

S U M M A R Y

Three environmental parameters suggest the high input of manhours into the creation and maintenance of such a landscape. Firstly, the amount of stone movement, mounding, walls, alignments, and terrace construction indicates a keen desire to utilise the landscape in spite of the extensive natural distribu­tions of basalt stone making it intially difficult to do so. Supporting this state­ment is a second factor, that of slope. The steepness of the terrain in this up­per region is such that the terracing and structural support using stone to face the fronts and backs of terraces, was a necessary action. The landscape, once cleared of vegetation, can be assumed to have suffered from a very high erosive action which would be compounded by a third environmental characteristic of the Waipoua district, that of high year round rainfall. Therefore, the com­bination of extensive stone work suggesting wide terrain exposure, high rain­fall and a steep angle of slope all indicate the need for either a high degree of maintenance of stone arrangements acting as soil catchments or the rapid abandonment of each newly created agricultural site (as soil was lost downslope) and the reorganisation of further areas of the natural landscape in the characteristically 'swidden' type of exploitation. In terms of man-power the former option seems less daunting, however, given the possible dilemma of erosion and soil loss the latter option may have been a necessity. Spectral tones therefore reveal considerable subsurface evidence suggesting prehistoric use of the lower river valley was well established when the upper valley was cleared and cultivated. Sediment from the upper valley has likely covered the surface evidence of prehistoric activity.

Also supporting the prehistoric antiquity of these features is local tradition which places the creation of the Takapotahoro drain, seven generations ago (Alex Nathan pers. comm. May 1986). It seems clear from the evidence presented above that the use of infrared aerial inquiry, has provided a more representative perspective of the prehistoric land use patterns of the Waipoua

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River Valley as a whole. Colour infrared vertical aerial photography has provided successful results

in a densely vegetated and complex landscape where ground visibility was ex­tremely difficult. Future applications to other complex landscapes and areas where ground investigation lacks financial backing, will be invaluable to archaeological research in New Zealand.

ACKNOWLEDGEMENTS

Thanks are extended to the Archaeological section of Auckland N.Z.ES. for providing finan­cial backing for this project. Alex Nathan has my gratitude for allowing a ground visit to the study area. Thanks also to Alex Brewis and Dorothy Brown for their comments on the draft of this article.

REFERENCES

Charters, A . H . , 1982: Site Management in Waipoua S.F. 13. A report to N.Z.F.S. (Auckland). Coster, John, 1979: Archaeological Sites in Established Pine Due to be Thinned or Clearfelled.

N.Z.F.S. Auckland file note 6/13/21/1, 13 August 1979. Coster, John, 1983: Archaeological Site Management in the Waipoua River Valley - a Review and

Proposals. Unpublished report, N.Z.F.S. Auckland, sample lot file A478/8.88 Keen, C , 1987: The Archaeological Application of Large Scale colour and Colour Infrared Aerial

Photography Over the Lower Waipoua River Valley. Preliminary Unpublished report to N.Z.F.S. (Auckland).

Lawlor, Ian, 1984: Waipoua Archaeological Project: Stage 1 Information Sheet. Unpublished report, N.Z.F.S. Auckland conservacy file 6/13/21/1, 5 November.

Moore, Annetta, 1984: Waipoua State Forest 13, Reconnaissance Survey and Site Management 1984 Planting Season. Auckland F.S. file A 478/8.

Papworth, Martin, 1980: Waipoua River Valley Site Survey, March-April, 1980. Unpublished report, N.Z.F.S. Auckland, N.Z.F.S. Auckland sample plot file A 478/8.

Pierce, Jill., 1982: Report on Trial Logging on N18/142 Pits/Terrace Site Cpt, 15, Waipoua S.F. 13. NZFS Auckland file note 6/13/21/1, 30 March 1982.

Tartaglia, L.J . , 1977: Infrared Archaeological Reconnaissance In Reports of the Chaco Center No. 2. Aerial Remote Sensing Techniques in Archaeology. Chaco Center N.P.S., U.S. Dept. of Interior, & University of New Mexico, Albuquerque.

Taylor, M . In prep.: Waipoua State Forest 13: Archaeological Management and Research Under­taken during 1985-86. Draft Report submitted to N.Z.F.S. (Auckland Conservancy).

Taylor, M . and A. Sutton, 1985: Waipoua Archaeological Project: Report on the proposed historic and traditional reserve in Waipoua State Forest 13, N.Z.F.S. (Auckland Conservancy).

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