High-Resolution Satellite Imagery in Archaeological Application: A Russian Satellite Photograph of the Stonehenge Region
Fowler, Martin J. R., Antiquity
The spy satellites - by repute of the thriller writers - have such good image-resolution that they can read the letters on a vehicle licence-plate. A generation after LANDSAT imagery vividly showed broad ecological zones, higher resolution pictures are now being released of a quality to allow practical archaeological application. The example printed here illustrates the Stonehenge landscape - a little patch of southern England that is among the most photographed archaeologically anywhere.
Archaeological potential of satellite imagery
Since the monument at Stonehenge was photographed 90 years ago from a balloon (Capper 1907), a light aircraft flying at low altitude has become the usual platform for aerial photography for archaeological studies. With the launch in 1972 of the first of the American LANDSAT series of satellites, a new source of remote-sensed data became available to the archaeologist in the form of satellite imagery from low Earth orbit.
The first LANDSAT satellites produced low resolution digital imagery with a pixel size approximating to 80 m on the ground. Ten years later, with the launch of LANDSAT 4 carrying the Thematic Mapper (TM) sensor, the resolution improved to 30 m and in 1986 the launch of the French SPOT satellite provided products with resolutions of 20 and 10 m. Since the break-up of the Former Soviet Union, high-resolution imagery has become available with nominal ground resolutions of 3-4 m or better (Fowler 1995a) and imagery from the early US spy satellite programme is also becoming available (McDonald 1995).
With early and low-resolution imagery, it was possible to see only very large archaeological structures such as the Pyramids at Giza (Quann & Bevan 1977); archaeological applications have attempted to exploit the multi-spectral nature of the LANDSAT and SPOT products through the use of image classification and modelling techniques (Ebert & Lyons 1980; Ebert 1989; Allen et el. 1990). In Britain, LANDSAT and SPOT images have been used to study areas of archaeological potential in the Cumbrian peatlands (Cox 1992), archaeological features in the eastern Fenlands (Shennan & Donoghue 1992), linear features such as Roman roads 'fossilized into the modern landscape around the Danebury hill-fort (Fowler 1994a), and the circular earthworks of the Figsbury Rings hill-fort on the Wessex chalklands near Salisbury (Fowler 1994b).
Satellite imagery of the Stonehenge environs
The immediate Stonehenge region includes upstanding features, crop- and soil-marks in relatively uncluttered grassland and arable. This region is well documented archaeologically (RCHM(E) 1979; Richards 1990; Chippindale 1994; Cleal et el. 1995) and represents a good area to see what archaeological features can be visible on satellite imagery.
An earlier study (Fowler 1995b) demonstrated that LANDSAT TM Band 4 imagery, covering the near-infrared region of the spectrum at a resolution of 30 m, shows areas of dark tone associated with round barrows in reserved areas of older grassland which have different spectral signatures to the surrounding fields. These areas are also visible to an extent on SPOT Panchromatic imagery (10-m resolution), where the highly-reflective visitor footpath around Stonehenge itself is most apparent. Apart from these examples, the low resolutions of the LANDSAT and SPOT products used in the study precludes the direct identification of archaeological features present in the area. Recently released Russian imagery, however, is comparable in detail with medium-scale vertical air photography and hence has the potential of directly detecting archaeological features.
KVR-1000 image and processing
Russian KVR-1000 satellite imagery is taken from an altitude of 210-235 km with a camera recording an area of 40x300 km on film at a nominal ground resolution of 3-4 m or better (Fowler 1995a). The panchromatic film, covering the spectral range 0. …