Aerial Photographs: Access and Use

A stereoscope, as pictured above, provides a means to view overlapping, vertical images and obtain a magnified, 3D effect (useful for assessing the depth of terrain).

Stereoscopes are available at CPNWS for use by researchers.

Example of an aerial photograph captured during the 1963-64 flight over Mt. Baker National Forest. The data printed at the top of this image includes: date of exposure, time, scale, flight code and roll/image number.

Image taken during surveying of the AL-CAN Highway, circa 1930s.

Aerial photo documenting the route of I-5 through Mt. Vernon, Washington, 1969.

This is a large and complex colllection, comprising over 30,000 images (around 60 boxes and 140 oversize folders of images and indices).

CPNWS staff will assist you in the following research process:

• Determining a) the geographic location and b) the time period for which you are seeking images. It is useful for researchers and CPNWS staff to have as much specific information as possible re: geographic names/features (e.g. towns, county, names of mountains, lakes, rivers), coordinates and/or Township, Range and Section information.  Depending on the available indices, it may be necessary to convert one type of reference to another. Google Earth and the online Earth Point tools are very useful for this.

• Using the online Guide to the Collection to identify an index (and corresponding photos) for an aerial survey documenting the relevant location and time period.

• Navigating the relevant flight index/indices to find:

• • flight code and other flight information
  • Line, roll and image numbers covering area of interest.

• Identifying images that correspond to the index. Note that coverage of some areas is incomplete.

An aerial survey and set of photographic images should be accompanied by an index showing the lines of flight and points at which images were captured. One of the first steps to accessing the aerial photos at CPNWS is to find an index for a flight covering an area of interest.

An index is typically a map or composite of aerial images showing the area(s) where a flight took place. On an index you may expect to find:

• Key identifying and contextual information about a flight, including flight code/symbol, date, creating agency and flight service.Markings showing the different and numbered “lines” of a flight.
• Periodic “image” or “sheet” numbers for the aerial photographs taken at a given point on a flight line.
• Sometimes (and with great variation!) names of geographic locations or natural features, township/range/section information, or latitude/longitude coordinates.

Example 1 (below). Section of index map for a 1963-1964 flight over Mt. Baker National Forest. This index provides a wealth of information about the flight, including its flight code (EMM), creating agency (USDA Forest Service) and scale (1:12,000). The vertical lines show North-South lines of flight and areas covered by the pilot during the survey. Numbered dots show the roll and image numbers, that correspond to the numbers of specific images captured at a particular point. This index map provides names of geographic features and also Township/Range information.

Example 2 (below). A section of one of six photo index sheets for a 1979 flight over Whatcom County (USDA Agricultural Stabilization and Conservation Service). Each numbered square corresponds to an individual aerial photograph. Since such an index may not provide names of towns or geographic features, the user must rely much more on visual cues and interpretation.