Green hell in red world


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Alluvial Placers
  Banka drilling
  photo geology
  seismic survey
  field manager

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The photogeology

The use of aerial photographs to obtain both qualitative and quantitative geologic information is referred to as photogeology. Aerial photographs are widely used today for identifying and mapping landforms, drainage patterns, structural features such as faults and folds, and rock or lithologic Units. Knowledge of the surface attributes of a landscape also enables a geologist to infer or predict subsurface characteristics and relationships. Airphotos are routinely scanned for the following types of geologic studies:

  • compiling topographic and geologic maps
  • exploring for mineral, hydrocarbon, and groundwater deposits
  • identifying hazardous features or sites such as active earthquake faults and areas prone to landslides
  • identifying and mapping landscape changes caused by a natural hazard event such as a hurricane or earthquake
  • selecting potential construction sites for critically engineered facilities such as dams or harbours.

    The geologic interpretation of aerial photographs is based on the fundamental recognition elements that include shape, size, pattern, shadow, tone or colour, texture, association, and site.
    The quantity and quality of geologic information that can be interpreted from aerial photographs is dependent upon the training and experience of the Interpreter in geology and remote sensing.

    The three-dimensional view of the terrain reveals important topographic information that cannot be obtained by viewing single photographs.

    Stereo photos.

    See for yourself, by gazing at the above photostereopair to see it in 3D.

    Although oblique airphotos are often of value to the photogeologist, most studies make use of vertical airphotos.

    Most of the photographs used in photogeology are acquired under relatively high solar illumination angles to ensure that ground detail is not hidden by cast shadows. When there is a need to enhance surface irregularities, special purpose photographs are acquired with low sun angle illumination. Whenever feasible, both high and low sun angle photographs are obtained for a given study area.

    Medium to large scale airphotos are best suited to the detailed study of a localized area, whereas small scale airphotos, such as those obtained from earth orbit, find their greatest utility for regional surveys.

    In photogeology, the convergence of information principle is often employed, whereby an interpreter starts with small-scale photographs for a synoptic view and gradually focuses upon a local or target area by interpreting successively larger scale photographs.

    Regardless of scale, however, it is important to remember that ground observations (i.e., field geology) can't be replaced by photogeology.

    Rafal Swiecki, geological engineer email contact
    January, 2011
    This document is in the public domain.