I need to georeference 53 air photos from 1981 (1:25,000 scale) and was wondering what would be the most efficient, defensible, and accurate option. For context, the air photos are following a highway taken along a valley bottom and therefore the relief would not be significant as would be the case if mountains were involved. Essentially, I want to quantify the change in surface area around this highway from 1981 photos to current day; how do I process the former images?

Typically, one would georeference each air photo using current satellite imagery. However, in my case, I feel this would be difficult because the area of interest has changed through time, and therefore I fear I will not have enough reference points from current satellite imagery to georeference each air photo from 1981. Therefore, I thought I could first stitch the 53 air photos together using control points from the adjacent air photo taken the same day; essentially creating a mosaic from 1981. Then I could georeference the entire mosaic using current satellite imagery; I think on a larger scale I could find enough reference points to accurately geofrerence the mosaic. Would this process cause too much local distortion that I would no longer be able to accurately quantify surface area? Lastly, I'm curious if orthorectifying the image would significantly improve the surface estimation? I'm not looking for complete precision, but would like it to be accurate enough for a publishable manuscript.

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    As I understand the process use Aerotriangulation to produce orthophotography. Although your photos are square the area 'on-the-ground' that they cover will not be due to terrain, you will need to ortorectify against some sort of elevation model to get them to sit right. There is special software to do that like Orthovista and I think ERDAS will do it too. – Michael Stimson Aug 22 '14 at 2:43
  • I have ArcMap 10.2 desktop (advanced). I haven't tried anything yet since I want to know the most efficient way first. I also have the DEM file for the area, but will need to obtain the air plane lens information if orthorectification is required. – LaurensP Aug 22 '14 at 3:58
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    ArcGis can do Orthorectification see resources.arcgis.com/en/help/main/10.1/index.html#//… provided you can get the coefficients in a format that it recognizes. If you can't get that and want to force it in you can use georeference with rubber sheet and piece the photos together like a jigsaw puzzle - do the images with similarities first against known data and then fill in the remaining images using similarity against the previously georeferenced tiles. I have used this approach with As-Constructed drawings and it worked acceptably. – Michael Stimson Aug 22 '14 at 4:06
  • As it stands I think your question is too broad because it includes a number of questions. I thought there was a possible duplicate of Software for Stitching Aerial Photographs? for one of them that I now think may not be the case after another read of your question. In any event I think your question will become more answerable if you research/ask each question separately in case any already have existing Q&As. – PolyGeo Aug 23 '14 at 4:09