Repeat Photography

Repeat photography as a scientific method has been around since the 1880s. Early users carried cameras up alpine slopes to document glacier growth and recession year after year. Botanists in the 1950s took up repeat photography to understand succession and landscape-scale plant population change. Public lands management agencies such as the United States Geological Survey and United States Forest Service have recently used repeat photography as a method to monitor management actions and to examine glacial retreat. More recently, repeat photography has been used successfully as a lens to understand cultural and urban change over time. For more information on formative titles in repeat photography, please see the blog entry in the field notes section.

What does repeat photography do for us? It offers us a selective view on the past. That the view is selective reveals a lot about the photographer. Each shot is an opportunity to inquire into why they framed that particular landscape and chose to capture a snapshot of that place at that time. In public land management scenarios, such as this one, that imperative is clear. Army Corps photos of the 9-foot project were meant as tools of legibility. They documented landscapes that they believed 9-foot project flood waters could impact. Photographing tract corners, houses, barns, and islands let the Army Corps know the landscapes they were about to own. It was, therefore, an act of control. 

The photos were not, however, meant to be used as a human and ecological bookmark. This unintended use allows us to look through the Army Corps’ lens from a different perspective - one that lets us know more about how these landscapes have changed over time.

Precise repeat photography requires that the photographer positions themselves in the exact tripod location, shoots the shot with a like camera format, at the same view angle, at the same time of day and year, and under the same weather conditions. There are clear comparative advantages to adhering to this strict methodology. By removing the variables of date, weather, and technology the photographer, in theory, has a precise lens to view change over time.

Any researcher engaging in repeat photography must ask themselves to critically examine their own goals for the project. Is precision the goal? For sure, relocating the exact shot was a priority of this research. Most repeat photography offer views of grand landscapes with distinct landmarks and clear lines of sight. More times than not, the shots contained in Two Mississippi were not grand and only occasionally were there distinct landmarks on the horizon. 

Each original photo did contain some locational data. When paired with historic plane table maps authored by the Army Corps 9-foot project survey crews, I was able to determine within a reasonable margin the location and lens angle of the original photo. Each photo point location was entered into a Geographic Information System database; this allowed me to export the locational information into a Garmin 64s GPS and later, an EMLID Reach DGPS. 

GPS got me close, but navigating by GPS under a tree canopy can be tricky business. I began to develop an eye for identifiable, albeit small landscape features pulled from the photos. From time to time I would find old USGS benchmark monuments half-buried in silt and sand and was able to match them up with coordinates on the historic plane table maps. Tree-blazes, notched by the Army Corps between the 1930s and 1950s to mark tract corners became my favorite companion - a sure sign that I was in the right place. I carried a metal detector along with me and spent hours scanning old farmsteads, now dense forests, for water pumps and barbed-wire fencing buried in the sediment. 

Photographing landscapes on a dynamic system like the Upper Mississippi made matching date, time, and weather a formidable task. The Army Corps shot most of their original photos in the winter and early spring; they strongly preferred leaf-off conditions in order to get an unobstructed landscape view. Extreme winter cold made some of my first attempts to “reoccupy” photo points grim experiences. Moreover, I had to come to recognize that the 9-foot project, levees, and climate change has completely altered the Upper Mississippi’s flood regime. Shot dates came and went while the river flooded. Ultimately I had to accept that I could not, and should not, pursue exact precision. As photographer Peter Goin said in Stopping Time: A Rephotographic Survey of Lake Tahoe: 

“the comparison between two landscape photographs, made on the same hour and day and from the same vantage point exactly seventy or eighty years apparently, provides a measure of the passage of time. Yet the landscape does not reflect the steady progress of the clock. Rather, time is measured by visual change in the landscape … recognizing the complexity of the concept of the time thus becomes increasingly important” (8).

Repeat photos were shot with a Canon EOS 6D with an EF 25-105 mm lens. To understand the visual change in the landscape I employed a categorical “mining” schema - discussed in the Methods section. Selected examples of photo pairs can be found in the Transformed Ecological Landscape and Transformed Human Landscape sections. A brief discussion of the original photos and plane table maps can be found in the Photos and Maps of the 9-Foot Channel section