The development of aerial photography and the extensive coverage that has been accomplished in recent years has stimulated the use of airphotos to facilitate engineering planning and construction. The basis of this phase of development has been the identification of features that bear a relationship to the texture of the soil pattern although they include such elements as land form, drainage, soil color, erosion, and vegetative cover. Land form identification does much toward establishing general conditions of soil depth and texture, while surface drainage indicates relative permeability. Gullies assume various shapes and thereby reveal not only certain properties of the surface material but the existence of clay-pan developments or unrelated materials occurring below the surface. Soil color is related to texture and ground water conditions, and vegetation is a variable depending upon climate and local influences.
Assembled evidence shows that most soils can be distinguished by characteristic patterns regardless of their geographic distribution. Photographs illustrate the similarity of patterns, and test data are presented to permit the evaluation of interpretation.
The use of this information contained in airphotos enables design and construction practices to be established in the early phases of planning peacetime construction or military operations. Grading estimates are made with varying accuracy, depending upon the quality of photography and equipment available, but detailed clearing estimates can be made from uncorrected photographs.