Photo interpretation, with examples of its usefulness

Abstract

In the following paper, the authors bring forward four examples of photo interpretation applied to limited problems, in order to show the value of conference in this matter. The kaolin deposit of Berrien (North Finistere), which is one of the most important in France, was detected through interpretation of the photographic image observed on 1961 air panchromatic and infrared plates, previous to the first investigations. The 1966 photographs bear out the location of this deposit. The highroad no. 76 displays an unsteady section over about 1 km long (0.62 mile), between Nerondes and La Guerche (Cher). The tectonic and structural causes of this instability are shown on the photographs, and draining works are suggested. The same also applies to the crumbling of the tunnel of Tendron which cuts across the fault of Milly, satellite of the Sancerrois fault. A geological study, followed by draining works under the tunnel, would have avoided such an accident, which has been immobilizing traffic for more than four months. Finally, photo interpretation analyzed the landslide located on the northern side of the Arre river valley (Gard), the surface of which is important (500 m long by 700 m wide—1,500 × 2,000 ft.); this landslide detached the limestones and marls of Liassic age, and hangs threateningly over the bottom of the valley. A few hours of conference were sufficient to analyze these phenomena and to understand their mechanism. During the previous meetings of Commission IV, we heard little of consultation and usefulness of photo interpretation. This paper intends to show, through limited and concrete examples, how a photo interpreter is able to deal readily and accurately with problems of economical value. In fact, a photo interpretation study does not necessarily result in a map but, within the consultation, in a scheme, a definition of the problem to be dealt with established by the expert, and the solutions to be brought in. This consultation is quite inexpensive, hence interesting. The orientation part played by the photo interpreter in the research is therefore essential.