Between 1990, when the first GPS-guided missiles were used in war, and 2001, when the United States began its invasion of Afghanistan, GPS guidance for weapons went from a niche technology used only by a few systems to one of the US military’s favorite techniques. The spread of GPS guidance led to a huge demand for ways of determining target positions in a way that weapons – rather than pilots – would understand. That meant three-dimensional coordinates in World Geodetic System 84 (WGS 84), rather than grid references on maps or even coordinates in other datums. One of the most important tools for establishing these coordinates was the Point Positioning Data Base (PPDB), a database of matching imagery and coordinates that had originated in the 1970s as a tool for army field artillery.
Made widely available in an analog format in the 1980s and used during the first Gulf War, PPDB’s digitization had restricted its use mostly to computer workstations (first DEWDROP, then RainDrop) in the United States during the war over Kosovo in 1999.
By the time the invasion of Afghanistan began in late 2001, RainDrop workstations had moved from analysts’ desks in the continental US to the same airbase – Prince Sultan Air Base in Saudi Arabia – as the air operations center that was commanding the air war. That shift was only the first step in the proliferation of tools and services for point mensuration to match the American and coalition demand for mensurated target coordinates. “Cursor on Target” (see Part One) began development in 2002; Northrop Grumman released RainDrop’s successor – RainStorm – in 2004; and another system, Precision Strike Suite for Special Operations Forces (PSS-SOF), was created to provide “near-mensurated” coordinates to troops in the field.
By 2009, when Noah Shachtman wrote a description of how mensuration was used to plan air strikes in Afghanistan, the process had been in regular use for almost a decade. Here’s his description of what was being done in the air operations center for Afghanistan:
An officer, I’ll call him Paul, walks me through the process. It starts with “targeteering,” figuring out where a pilot should attack. Just getting GPS coordinates or an overhead image isn’t good enough. GPS is unreliable when it comes to altitude. And landscape and weather conditions can throw satellite pictures off by as much as 500 feet. “Even with Gucci imagery, there’s always errors,” Paul says. He points to a pair of screens: On the right side is an aerial image of a building. On the left, two satellite pictures of the same place — taken from slightly different angles — flicker in a blur. Paul hands me a pair of gold-rimmed aviator glasses. I put them on, and those flickers turn into a single 3-D image. Paul compares the 2-D and 3-D images, then picks exactly where the building should be hit. Depending on elevation, adding a third dimension can shrink a 500-foot margin of error down to 15 feet.
Tying a point on the ground to a global grid precise enough to be used for air strikes anywhere in the world was now a matter of course. Fifty years after the CIA’s photo interpreters bought their first mainframe to help them analyze and map targets in the Soviet Union, calculating a target’s position in global terms has become simple – even if knowing what is at the target location is not. The technology here is also a long way from the cobbled-together equipment for which the PPDB was first created. The Analytical Photogrammetric Positioning System (APPS) combined digital and analog electrical components with old-fashioned optics and the human eye.
The transformation from APPS to RainStorm over the course of thirty years is pretty remarkable, but its also been hard to track. This is technology that doesn’t get a lot of praise or get singled out for attention, but that doesn’t mean its not interesting or important.
For one thing, APPS was a military application of commercial off-the-shelf (COTS) technology before COTS was cool. The Hewlett Packard 9810A desk calculator at its heart was not designed for military use or developed from military-sponsored research. It was just an office tool that was re-purposed for a very different office.
More importantly, APPS and PPDB are a good example of an enabling technology that was created long before its eventual requirement even existed. If there had been no PPDB, the development of GPS-guided bombs would have forced its creation. Instead, it was an Army project begun around the same time the first GPS satellites were being designed that provided the necessary service. That’s luck, not good planning.
Lastly, and equally interestingly, PPDB is a layer of complexity in modern warfare that’s easily overlooked because it sits in the middle of things. It provides the map of coordinates on which grander, more significant, moves are sketched, and which disappears into obscurity except when something goes wrong. Between cursor and target, or sensor and shooter, there are a lot of layers like this one.