Aerial Photography

Barri Jones (1936 - 1999) was Professor of Archaeology at Manchester University from 1971 until his death. He was interested in frontier regions, and dug extensively inWales, north-west England and the Pennines. His early work in Apuliain the 1960s had given him great skill at interpreting air photographs, and he developed excellent skills as an aerial photographer. He flew scores of sorties himself and, when flying was too expensive (he funded most of the work himself), he improvised, devising his own radio-controlled camera carried by a kite. In Scotland and Cumbria he concentrated on Roman military sites, charted the westward extension of Hadrian's Wall, investigated settlement on both banks of the Solway and, more controversially, followed the tracks of Agricola's adventures in Scotland, all the way up to the Moray Firth. He photographed sites in Dumfries and Galloway in the 1970s, from Birrens Roman Fort in Annandale in the east, to Rispain Camp at the foot of the Machars in the west, including sites which are only visible as cropmarks and those which are upstanding earthworks. He often followed up his aerial discoveries with targeted trial excavations, and the results transformed our knowledge of settlement in these frontier regions. In 1985 he co-authored a book on Roman Cumbria, 'The Carvetii'.   Aerial photography mostly records variations in vegetation growth, seen as cropmarks, which can give indications of surviving archaeology below ground for which there is no visible evidence on the surface. Cropmarks result from variation in the depth of top soil  and consequently the amount of water in the soil, causing variation in crop growth particularly during periods of dry weather. Buried ditches for example show as dark lines, since the deeper depth of soil in the filled-in ditches retains more moisture than the surrounding soils, and therefore crops above them remain greener longer. Parchmarks are a variant form of cropmark, and indicate areas where walls or other impervious structures survive below ground level, thus reducing the water-retention capacity of the subsoil.  This means that in particularly dry weather these areas will dry up faster, leaving pale lines to indicate the location of the sub-surface features.  Although often visible on the ground, these marks are also visible from the air, where it is often possible to make sense of the forms and patterns, and so produce an interpretation of the buried site.