Answer: A. Aerial photographic survey
Reconnaissance is best done with the help of aerial photographic survey.
When the distance and area to be covered are great, aerial photographic surveys are very well suited for preliminary surveys. The survey could be broken down into the subsequent stages:
- Using an aircraft to take aerial pictures of the surveyable land strips with the necessary longitudinal and lateral overlaps. For the creation of mosaics, vertical images are required.
- Control points are chosen to establish the traversal of the alternative proposals once the images have been evaluated using stereoscopes. The maps show where the control points are.
- Spot levels and subsequently contour lines may be derived using stereo-pair observations. The topographical information on the maps can also be recorded using the stereo pairs.
- To evaluate the geological features, soil conditions, drainage requirements etc., photo-interpretation techniques are applied.
Reconnaissance: The reconnaissance survey is a thorough examination of a large region that could be utilized as a road or an airport. Its goal is to find the more promising routes or places while eliminating the impractical or unworkable ones.
Hence, we can conclude that reconnaissance is best done with the help of aerial photographic surveys.
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