Culture and Ecology of Chaco Canyon and the San Juan Basin

--------- - --The NPS Chaco Project 11Table 1.1. Sets of aerial photographs of Chaco Canyon and selected outlying Chaco an sites.Source Date Scale TypeSoil Conservation Service 1930s 1:62,000 Black-and-whiteSoil Conservation Service 1930s 1:32,000 Black-and-whiteU.S. Geological Survey 1950s 1:32,000 Black-and-whiteU.S. Geological Survey 1971 1:3,000 Black-and-whiteKoogle and Pouls 1973 1:3,000 Black-and-whiteKoogle and Pouls 1975 1:3,000 Black-and-whiteKoogle and Pauls 1975 1:1,200 Black-and-whiteKoogIe and Pouls 1973 1:6,000 Color transparencyRemote Sensing Division 1974 35 mm oblique images Color infraredthen-available sets of aerial photographs for ChacoCanyon and selected outlying Chacoan sites by date,scale, and type.Different types of film have distinct advantages.Black-and-white panchromatic is best suited for mostpurposes; it is low in cost, readily available, easy touse, and non-grainy, and has overall good contrast andresolution. Black-and-white infrared is more sensitiveto vegetative differences and is less affected by haze.True color imagery is more expensive, but the subtlecolor changes make it easier to detect vegetationdifferences. False color infrared is most useful forplant detection (Lyons and Avery 1977). Potter andKelley (1980) analyzed color transparencies at a scaleof 1:6,000 to create an initial vegetative cover map ofthe canyon. Jacobson (1979; in Mathien 1991a:348)found that color transparencies at 1: 1200 were moreuseful than black-and-white images when mapping asmall site prior to excavation because color differencesare more easily distinguished by the human eye thanedges among shades of gray. Lyons and Hitchcock(1977b) used existing black-and-white photographs at1:3,000 and 1:32,000 to discover a number of roadalignments within Chaco Canyon and the local area;Obenauf (1980b, 1983b) expanded this analysis tocommunities in the San Juan Basin. Nials (1983:5-15to 5-16) emphasized the importance of the timing ofphotographs when looking for linear features. Thelow-sun-angle black-and-white photographs used inthe Bureau of Land Management roads projectrevealed alignments that were not seen in photographstaken later in the day.Aerial photographs serve many purposes.Because accuracy in site location is important,handheld 9x9 in prints are easy to carry and providepermanent records; data can be transferred to mastermaps in the laboratory. This proved useful during theChaco roads survey and a survey of the lower ChacoRiver (Loose and Lyons 1976a, 1976b). An analysisof 1 :6,000 photographs of features in the Kin Bineolavalley, particularly those relating to the prehispanicirrigation system (Lyons, Hitchcock and Pouls 1976),compared favorably with data obtained from thecomprehensive survey of the area by Hayes (1981). Ifground control is set up prior to photographY, it isrelatively simple, rapid, and economic to derivemeasurements for nonstandard contour intervals(Drager and Lyons 1985; Lyons and Avery 1977;Pouls et al. 1976). Orthophoto maps and photogrammetricmaps can be digitized and the data usedfor various purposes (Drager and Lyons 1985). Slopedetermination, volumetric measurements, or populationestimates can be obtained (Drager 1976b). AtPueblo Alto, photogrammetric maps before excavation,after wall stripping, and after the secondseason of excavation provided a permanent record ofsite condition. Detailed photogrammetric maps oflarge pueblos and digitization of their architectural