Manual Photographic Search in Imagery: Logical Deductive Search and Fishing Expedition (Especially for GATE-Geospatial 2022)

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Steps in Logical Search

  • The interpreter should always keep in mind the basic qualities of the imagery they are dealing with, e. g. film filter combination, the season and time of day of acquisition, and the image scale, etc. In addition, the interpreter should always remember to examine all the titling information on an image.
  • Interpretation should begin with the general and proceed to the specific. After gaining an overall impression of the photograph the interpreter should begin to examine the physical features (e. g. water bodies, mountains, forests, etc.) and cultural features (e. g. urban areas, farms, road networks etc.) . The interpreter should then move to more specific questions e. g. what types of trees make up the forest? What types of roads are present?
  • Interpretation should be conducted logically one step at a time. Following from above it is good to go from a detailed examination of landforms to vegetation, to hydrology and so on. Then address cultural features in the same fashion. What types of urban features are present single-family residences, multi-family residences, industries, retail districts and soon?

Techniques of Image Search

There are basically two techniques that people tend to follow when searching for imagery. One is logical search and the other can be termed the “fishing expedition.”

Elements, Techniques, Aids, Methods and Procedures

Fishing Expedition

In the fishing expedition, the interpreter searches the imagery in a random fashion attempting to find recognizable features or object that will lead to whatever the interpretation goal happens to be. At some point, even this type of interpretation begins to logically converge. Patterns of anomalous vegetation may lead to looking for water sources, which may lead to looking for transportation systems, illegal growing etc. Logical search is a more systematic method of analysis most often used by interpreters.

Logical Search

The logical search involves these things:

  1. The interpreter should always keep in mind the basic qualities of the imagery they are dealing with, e. g. film filter combination, the season and time of day of acquisition, and the image scale, etc. In addition, the interpreter should always remember to examine all the titling information on an image.
  2. Interpretation should begin with the general and proceed to the specific. After gaining an overall impression of the photograph the interpreter should begin to examine the physical features (e. g. water bodies, mountains, forests, etc.) and cultural features (e. g. urban areas, farms, road networks etc.) . The interpreter should then move to more specific questions e. g. what types of trees make up the forest? What types of roads are present?
  3. Interpretation should be conducted logically one step at a time. Following from above it is good to go from a detailed examination of landforms to vegetation, to hydrology and so on. Then address cultural features in the same fashion. What types of urban features are present single-family residences, multi-family residences, industries, retail districts and soon?

Convergence of Evidence

  1. Image interpretation is basically a deductive process. Features that can be detected and identified lead the interpreter to the location and identification of other features. This is convergence, and for many applications of air photo interpretation, this involves the activities of one or two individuals synthesizing a large amount of information.
  2. Deductive interpretation requires either the conscious or unconscious consideration of all the elements of image interpretation. The completeness and accuracy of an interpretation is in some measure proportional to the interpreters understanding of the “how and the why” of the elements, techniques, and methods of interpretation.

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