Advantages of Photogeology Over Conventional Geological Survey
Photogeology, or aerial photo-interpretation applied to geological work, offers several advantages over conventional geological fieldwork. While there are some disadvantages, the main advantages are as follows:
1. Economy of Time
Aerial surveys, though initially expensive, are extremely rapid. A single airplane flight can cover thousands of square kilometers in a day, whereas a ground survey would take years. For instance, during oil exploration in the Sahara desert, aerial photography became a key tool, allowing the construction of accurate geological maps necessary for prospecting. These maps sped up the work significantly, allowing oil companies to save both time and money. For example, in the Sahara desert, photogeological surveys resulted in a three-quarter reduction in time and money compared to manual fieldwork.
2. Economy of Money
While the initial investment in aerial surveys may be higher due to the cost of airplanes, cameras, and related equipment, in the long run, the overall expense is significantly lower than that of traditional fieldwork. Once the cost of equipment is covered, the multipurpose nature of aerial photographs makes this method more economical.
3. Greater Accuracy
Maps created using photogeological techniques are generally more accurate than those produced by conventional methods, as human error is reduced. Boundaries between geological formations, field objects, and cultural features are reproduced precisely in aerial photographs. Although errors can occur in oblique or vertical photographs due to relief displacement in areas with high relief, these errors can be easily corrected using photogrammetric instruments. Close cooperation between field geologists and photogeologists ensures better accuracy through field checks and the use of all available geological information during photo interpretation.
4. Three-Dimensional Vision and Stereoscopic Depth Perception
A unique advantage of photogeology is the ability to create three-dimensional models under a stereoscope. Aerial photographs viewed as stereo pairs provide a “Bird’s Eye View” of the terrain, offering a sense of depth and vertical exaggeration. This stereoscopic vision is especially useful for interpreting regional features such as folds, faults, unconformities, and geomorphic features like domes, basins, plains, and plateaus. A geologist can get a comprehensive view of the terrain before conducting fieldwork.
Limitations of Photogeology
Despite the many advantages of aerial photo interpretation, certain drawbacks and limitations must be considered. While these limitations can be mitigated, beginners in photogeology should be aware of the following issues:
1. Non-Uniform Scale
The scale of aerial photographs is not uniform. It can vary from strip to strip, photograph to photograph, and even within the same photograph at different points. This non-uniformity can complicate accurate interpretation across a wide area.
2. Limited Use for Minor Structural Features
Photo interpretation is not very effective for identifying minor structural features unless the scale of the photograph is sufficiently large. Small-scale geological structures such as minor folds, joints, lineation, foliation, current bedding, and ripple marks are often not captured in sufficient detail on standard aerial photographs.
3. Difficulty in Rock Identification
In some cases, accurately identifying rock types can be difficult, especially if the rock exposures are covered by surface materials such as soil, vegetation, or other obstructions. This limits the effectiveness of photo-interpretation for direct rock classification.
4. Surface-Only Observations
Photo-interpretation only reveals surface features. Subsurface geology and structural features can only be inferred based on physiographic and structural indications observed on the surface. While helpful, this limits the ability to fully understand the geology without additional techniques or tools.
Though these limitations hinder the effectiveness of photo interpretation, they can be addressed to a large extent by combining aerial surveys with periodic field checks. This integration allows for more accurate and reliable geological interpretations.
