Geomorphological and Geoforensic Interpretation of Maps, Aerial Imagery, Conditions of Diggability and the Colour Coded RAG Prioritisation System.

Some geological techniques, conventionally used in mineral exploration and geotechnical ground investigations, are applicable to searches where there is a desire by the law enforcement to locate victims, objects or items buried or concealed beneath the ground surface. The objective of this paper is to draw attention to the applications of three methods that have been used as part of law enforcement searches. These are the geomorphological interpretation of high resolution air photograph, topographic and geological maps, the determination of diggability and the use of the RAG (Red-Amber-Green) prioritization system (known also as the ‘traffic light’ or ‘Go-No-Go’ system).

The acquisition, analysis and interpretation of aerial imagery, by a geologist and the law enforcement agency may provide a useful reconnaissance technique to help delineate and prioritize search areas. This is because burials in the ground may leave behind obvious ‘scarring’ of the ground or subtle topographic ‘disturbances’. Any such observations are considered in association with any natural geological processes of weathering and erosion.

A ground diggability survey will provide information on the ease and efficiency by which the ground (weathered rock, superficial deposits, soils or artificial ground) may be dug and reinstated by an offender(s). It is dependant on a number of factors that include; the depth of the soils, geology, groundwater, obstructions, digging implements used, ability of the offender, nature of item being buried and time frames involved. The results of a diggability survey may conveniently be presented as a RAG map which can help to prioritize the search.

The RAG system appears to have been used independently by geologists, law enforcement and the military, and has evolved differently since the early part of the 1900s. The origins and evolution of the RAG system are explored in this paper and this, along with the geological analysis of maps, aerial imagery and the determination of the diggability of the ground, have been applied to law enforcement searches for graves and other buried objects, as demonstrated by operational case examples.