Early in 2009, a control densification survey was conducted in Iraq near the Baghdad International Airport in support of engineering survey activities at the various coalition military bases located there.
Geodetic surveying is an exercise in patience on active military bases. Jamming, tracking and communications signals all compete with GPS signals for recognition.
While private sector land surveyors typically work on local and ground-based systems, the government, including the military, tends to work on geodetic grids. Working on a grid system means using GPS whenever possible. With previously set control disappearing in Iraq’s dynamic landscape, it is up to the survey groups deployed at any given time to maintain, re-establish or create control in order to keep projects moving forward.
There are several survey groups working in theater at the base complex in Baghdad, all with different missions. The group to which I belonged was charged with establishing a survey control network linked to the country’s HARN as well as the active local CORS in order to provide control for as many of the survey groups in the area as possible.
Limited resources, slow-moving convoys, radio frequency interference, security concerns and, of course, weather all contributed to the challenge of establishing survey networks in a war zone.
Plan of ActionMonumentation was our first concern. It had to be substantial to remain undisturbed in this country. It had to make geometric sense for a network. It had to be accessible for GPS observations. It had to have the military’s blessing. And it had to be accomplished with the resources at hand.
Borrowing information from the NGS Web site, we wrote up specifications for the monuments. We then selected areas where we wanted to set the monuments, and we visited those areas to see about the permitting process. Eventually, we were able to obtain permission from the military to set most of our monuments.
Once the specifications and the locations were decided, service requests were filled out and sent to the construction laborers who made and set the monuments. In Iraq, plans are, in some cases, considered to be guidelines--suggestions. The monuments we requested were not like any monuments we had ever seen in the U.S. But they were excellent!
Each monument was a meter in diameter, starting with a rebar cage that, upon first glance, looked like a giant bird cage. The “bird cage” was set with a backhoe at a meter-plus depth and filled with concrete to complete the monuments. The top collar portion of the monument was a smaller diameter, less than a quarter-meter, also concrete with rebar reinforcement. And a survey cap was set on rebar sunken in the middle flush with the concrete surface. These monuments were placed so that dirt covered most of the monument with only the top collar showing.
This type of placement proved handy since at least three of these monuments were run over by Humvees, backhoes and front-end loaders within the first three months of their placement.
After monumentation, a survey plan was developed to accommodate inconsistent resources. We had several Leica System 1200 GPS receivers available to us, but only two surveyors and one truck. We borrowed a second truck for part of the fieldwork and accomplished it in three long days. We used static sessions tying to two known stations per session and repeating a percentage of the observations, rotating receivers and tying to different control in order to catch the possibility of blunders, equipment problems, and moving control points.
Similar to the saying about a battle plan--it’s only the plan until you get to the battlefield--our schedule was a living thing that changed as we surveyed. In the end, the field modifications to the plan worked, still providing redundant observations for an adjustment. One of the new monuments was not positioned, so it became a mystery station. After three observation sessions at different times with three different receivers, no data were logged on our mystery station--though another station very close to it logged data without incident.
Observation logs were kept for each occupied station and contained both vicinity and horizon sketches. Photographs for data sheets were taken where possible during the field observation sessions. The fieldwork went relatively smoothly, with the timeline being the most dynamic area of the plan.
Back at the office, which was located in a trailer among many other trailers that were all powered by generators, processing began. An adjustment was built in the Leica Geo Office software (LGO) and tested using LGO as well as programs from the NGS Web site.
Modified data sheets were developed based on military forms then populated with information about the new control stations. A report was written that included a table of control station positions in geodetic and grid coordinates, including both old coordinates and the new ones we had established, a map of the new station locations relative to the existing control, a table of the new stations, and the data sheets containing driving directions and photographs of the new control points.
The tables of the control stations were distributed to several survey groups at the bases, and copies were maintained in the engineering offices. Plans are under way to expand the control net to other areas in the country, tying to the existing HARN or CORS where possible. With luck and the continued efforts of the surveyors in Iraq, these control points will survive and be perpetuated during the years to come for mapping and reconstruction projects.
For the DurationIt is a daunting effort at times. As I drove by one of our new monuments shortly after the survey, I saw a backhoe making its way slowly toward the monument as part of a road construction project nearby.
The control survey was conducted in January. By May, one monument was missing some of its concrete from being run over by heavy equipment. Additionally, a radar site was erected across the road from the station. I also noted--to my initial alarm--that one of the automated defense weapons near that station tracks surveyors and locks onto the base receiver when set over the station. That station is in a very good position for GPS surveying, but I stopped using it nevertheless.
Another monument stands amid deep tire ruts from construction equipment. A third monument was set in a concrete pedestrian bridge that was out of the way of nearly everything. Not long after it was positioned, the bridge became a repair project--in the same area of the bridge as the disk. Fortunately, the construction did not disturb the station.
As of May 2009, the monuments had held up and had provided good positions for surveys tied to them. Perhaps geodetic surveying on bases in Iraq isn’t just about patience, but also endurance.