Creating Orthomosaics from Historic Aerial Imagery

Creating Orthomosaics from Historic Aerial Imagery

Bradford Washburn was a mountaineer, scholar, scientist, and photographer who climbed Denali multiple times. His wife, Barbara Washburn, was the first woman to climb Denali. Bradford Washburn’s map of Denali is still in use today. Denali National Park houses hundreds of historic images, including images Bradford Washburn used to make his maps of the park. Some of the images have started to deteriorate due to their old age. My project is to preserve historic aerial imagery stored in Denali National Park’s resources building by scanning and processing them so that they may be used for digital mapping and other studies. The topographic map shown below was made using historic aerial imagery taken August 27, 1952, by the U.S. Air Force.

Section of USGS Mt. McKinley (B-2) Quadrangle Alaska-Fourth Judicial Division 1:63 360 (Topographic) map

I scanned three different image datasets at 1200 dpi and created metadata for each image, including flight lines, photo numbers, notes written on photos, and other relevant information. Since Denali did not have all the images from the August 27, 1952, flight, I downloaded the rest of them from the USGS EarthExplorer database. I used a resize image python script to resize all the images so they could be aligned in Agisoft Metashape. Once the images were aligned, dense cloud, mesh, and digital elevation models were made. Orthomosaics, also known as orthophotos and orthoimages are the result of stitching together multiple overlapping aerial photos with distortions removed. Orthomosaics are complete and continuous image representations which can be georeferenced in ArcGIS Pro and given coordinates by picking multiple ground control points. This project is important for preserving the history of Denali and for future studies to compare present day images to historic images to see changes within the park. Below is part of the August 27, 1952, orthoimage I made of Wonder Lake and The McKinley River; compare it to the modern satellite imagery beneath it.

orthoimage of Wonder Lake from 1952 U.S. Air Force images

Landsat satellite imagery of Wonder Lake, Denali National Park, 2017

In addition to my main project, I have been working on smaller projects, such as collecting GPS points at the East Fork turnaround, updating Python scripts from Python 2 to 3, extending flight lines over Muldrow Glacier in ArcGIS Pro, and joining Park Geologist Denny Capps with his geology crew to observe landslides. If the weather cooperates, I will fly over the park road and Muldrow Glacier in Denali National Park’s plane.

Me at East Fork with a GPS

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