EROS Data centre is the location of possibly the largest archive of satellite imagery in the world. It was built in the early 1970s when satellite imagery was starting to be collected routinely at the global scale, and one of the USA’s most ubiquitous sources of satellite imagery had been Landsat. I had used it ever since I learnt how to be a remote sensor in the early 1990s. They chose Sioux Falls because they wanted a location which was relatively central to the North American continent to capture the data and download it as the satellites passed overhead. Not only did they download the imagery, but they archived it, and copied it for others to use. I remember waiting weeks for data to arrive on large spools, then tape cassettes, then CDs and DVDs. Now mostly it can be downloaded from the internet.
The storage of all those data was a massive challenge to EROS – especially since those satellites kept on just collecting day and night (even at night you could obtain radar and thermal images). Underneath the building a basement capable of resisting a nuclear explosion was created and Gray took me down there as part of my tour. Big parts of it were now empty, but at one time, Gray said, he could remember when every inch was covered in shelf after shelf of cassettes or spools. Now, he joked, we might as well set up some bowling alleys down here. Later he took me upstairs and looked through bullet proof glass at a large room which contained just two large supercomputers. They now contained many times more data than the large basement had ever held in the 1990s.
Back down in the basement, though, was a fascinating archive of the oldest imagery. There were plastic and metal canisters that contained original film from the early satellites, including from US surveillance forays of Russia and China with the Corona satellite. The images were parachuted back to earth on film negatives. Along another row we came across envelopes of the original Landsat MSS imagery again with negatives in. Gray knew his way around many of these shelves, he was an old remote sensing hand and had spent many an hour searching for imagery he wanted along the aisles. But when I looked up and down the shelves I saw they disappeared several hundred feet off into the gloom. Even now, the physical archive was enormous, and the USGS had not got around to digitizing the whole lot.