The U.S. Department of Agriculture Aerial Photography Field Office (USDA APFO), is the primary physical repository for color-infrared (natural color and black and white), photography captured from 1955 until recently when digital capture became the standard. Many of these photos were acquired in support of Farm Services Agency (FSA) and one of its predecessors the Agricultural Stabilization and Conservation Service (ASCS) programs in the post Depression and Dust Bowl era. That is to say that they were not originally collected for public access and consumption, although they undoubtedly have high public interest. Many APFO photographs have been digitized to some minimum resolution and public access provided through agreements with other federal agencies like USGS through the EarthExplorer web interface, as well by through APFO directly. Some institutions (like state government and academic libraries), that hold historic aerial photograph prints have also undertaken large digitization campaigns and posted their results online or in some cases kept them behind secure firewalls for members of their institution only.
For photographs that are already available online, digitization and posting largely took place some years ago when computer storage and internet access speeds made working with the large file sizes of digital images challenging. Furthermore, this was also a time-period when scanner technology was still in its infancy and scanner properties like the ability to preserve the geometric accuracy of the original film or image was not very good. Many projects digitized old photograph prints rather than film and in these cases there’s also the issue of printed material not being very stable — it often expands and contracts over time, sometimes warping in ways that can compromise the integrity of the geospatial information captured on the original film. Film isn’t perfect either, but at least it is the original picture without the compounding negative effects of printing, storing printed material, and then imperfect scanning of prints.
Many APFO photographs that are currently available online (e.g. from USGS EarthExplorer or Penn Pilot), were digitized at 600dpi or less and were digitized with scanners of unknown, or common desktop scanner properties. The image resolution and scan quality of these collections is fine for general inquiry, but the original film contains much more geospatial information than can be deciphered from a 600dpi low-quality scan.
Fast-forward to the present day and the 30+ year old film is starting to deteriorate (it can start to liquefy and smell like vinegar!), and APFO is in the process of moving their headquarter offices. For these (and other?) reasons they are in the midst of a massive digitization campaign with preservation in mind; meaning that they are using the highest quality photogrammetric scanners to digitally capture the original film at over 2,000dpi. To my knowledge there are no plans to post these images online, but they are free to the public if you request them from APFO and pay for the storage (i.e. external hard drives), a nominal fee for their services to load the drives, and shipping to get them to you. That said, they are far from free to produce as the scanners being used often cost more than $60,000 not to mention other supporting computer equipment and staff time. Compared to licensed geospatial data, they’re relatively affordable, but then again, in their native form they’re not really geospatial data at all because they contain distortions and lack geographic reference.
Take a look at the difference between a 600dpi image downloaded from USGS Earth Explorer and the image that I recently acquired directly from APFO. This is the neighborhood where I live in State College, PA and I’m not sure that I can even identify my house on the 600dpi image.
Fig 1. 600dpi image downloaded from USGS EarthExplorer
Fig 2. 2,032 dpi image acquired directly from APFO captured from the original film on a photogrammetric scanner
I can clearly identify my house in the second image above and we can zoom in even more to barely identify individual cars in the figure 3 image. The spatial resolution of this imagery given the original camera used, altitude of photo capture, and digitization specifications is about 0.7-meters, or about 2-feet. That means that each pixel in these images depicts an area on the ground of about 2-feet by 2-feet. Cars are then represented by about 2 pixels wide by about 3 or 4 pixels long. Any object smaller than about 2-4-feet will not be decipherable from this imagery. That said, for going back in time 30-years, this is pretty good! Neighborhood scale to car scale, that’s the difference between a 600dpi scan and a 2,032dpi scan of aerial photography film.
Fig 3. 2,032 dpi image acquired directly from APFO captured from the original film on a photogrammetric scanner
We have acquired the 2,032dpi imagery for all of Pennsylvania — in total they number 2,607 images. The capture dates range from March 27, 1980 to May 13, 1987 with an emphasis on capturing “leaf-on” or vegetative growing season conditions because again, these pictures were largely taken to support Farm Services Agency operations having to do with agricultural production. The complete metadata for the imagery that we acquired is available here and the imagery collection can be searched and downloaded directly from the PASDA Imagery Navigator. To search the Imagery Navigator, zoom and pan to your area of interest and then right-click on the map to see what imagery is available for that place and date. A pop-up window with years will appear and the 1980s color-infrared imagery that is the subject of this post is available for download from the “1980-1987” tab. You may get multiple image tile results for your area of interest because these photos were intentionally overlapped when captured (more on this important property of these photos in a latter post).
To see the approximate footprint coverage area for the 1980s photography in the Imagery Navigator use the “Display Tile Index” drop-down menu and select “Infrared 80-87 (approximate)”. These are approximate coverage areas for each photo because they are not georeferenced. There is no way to search photography coverage for lines or polygons. Pay attention to the footprint for the tile that you download to get an idea of where to start looking for your area of interest after you download the image — this is often a challenge because of how the photos are oriented and because they lack any place names or other labels to help you — they’re just a photograph.
Once downloaded, you’ll have to unzip the file and open it in any image viewing and/or editing software. When in doubt, try double-clicking on the file and then wait patiently for a bit — these are very large files that may bring you’re image viewing editing software and/or computer to a crawl. I’ve had good luck using both GIMP2 and IrfanView softwares, both of which are free and can be found easily with a google search.
If you know the photo tiles that you need, you can bulk download files from the PASDA ftp site.
For assistance searching, accessing, and using these photos, please visit the Donald. W. Hamer Center for Maps and Geospatial Information, or contact Nathan.
We are also in the process of developing efficient workflows to georeference these images and remove some distortions so that they can be incorporated directly into a desktop or web-based geographic information system (GIS) — or so that you can view the imagery as a background image in the PASDA Imagery Navigator.
Next post I’ll detail another new acquisition of historic aerial photography from the APFO — this time from the 1950s…
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