On February 22, 1986, the first commercial satellite, SPOT, was launched, and two days later on February 24, 1986, it began transmitting images back to Earth, and so began a new era in the long history of surveillance from the skies. What was once only available to only the most powerful militaries was now a commercial product available to businesses, to academics, and even to the public. While the number of images was initially a trickle, over the years more satellites were launched, more companies entered the market, and eventually the trickel became a flood. In a single generation we have moved from a world where space imagery, or aerial imagery of any kind, was rare and exotic, to a world where you can pull up a relatively recent image from space on your phone.
Not surprisingly, satellite imagery focuses on population centers, or on areas that are important in the news. Some companies use a standard collection plan, and others collect on a more ad hoc basis as a result of customer requests. There is not one business model for commercial satellite imagery production, there is no centralized requirements list that drives commercial satellite imagery collection, and there is no central repository for these images. As far as commcercial satellite production is concerned it is still a little wild, wild west in the cold reaches of near Earth orbit.
An unintended result of this competition is that for any given region on Earth, the location of maximum and minimum collection is totally unintentional. I will explain this more fully in a later post, but essentially it works out as follows: since there is no coordination between providers or clients, the location of images in time and space overlap in random and unintended ways.
The image above is the beginning of an exploration into where these unintended places are located, and into what is there. It is not a representation of images themselves but rather of their location, or what is often called their footprint. The image represents the overlaps of 49,141 images taken in the first 25 years of commercial satellite imagery, from the satellites operated by Astrium (SPOT 1-5, KOMPSAT-2), Digital Globe (QuickBird, WorldView-1, and WorldView-2), and GeoEye (GeoEye-1, and IKONOS). I'll get into the rationale behind this listin a later post, along with alternative lists. No matter how you lok at it though, this dataset is a pretty good start. Because of the limitations that I had on processnig power and time this image was created by converting each footprint, which is essentially an outline, into a grid of pixels, or also know as a raster, and then adding all of these pixels together. Again, more on this later.
The result is an image where the light areas represent areas on the Earth that have been photographed many times and the dark areas represent areas on the Earth that have been photographed few times. As this project progresses I will be experimenting with different ways to visualize and interpret this dataset, but even in this raw form strange and interesting patterns begin to emerge. These kinds of effects nearly always happens with this kind of data analysis, and I will be exploring some of the followon effects of these anomolies later.
For now I invite you to explore and ponder this strange artifact of a quarter century of human exploration.
Monday, March 12, 2012 at 08:04PM 
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