UAS Topographic Mapping in Afghanistan
When we think of drones flying in Afghanistan, the picture that does not come to mind is a 2-pound unmanned aerial system (UAS) being utilized to support engineering applications. But that is just what the 34th Forward Engineering Support Team – Advance (FEST-A) is doing.
The 34th FEST-A is a U.S. Army Corps of Engineers (USACE) unit comprised of two military personnel and six USACE civilians. This technical engineering team represents disciplines ranging from civil, structural, mechanical, electrical, environmental and geospatial engineering. The mission of the 34th FEST-A is to provide rapid and expeditionary engineering, design, construction, cost estimating and technical assessments in support of the U.S. military throughout Afghanistan.
The idea of incorporating UAS into the team was born of a practical necessity of operating in a contingency environment. The team, primarily consisting of unarmed civilians, found itself being tasked with missions “outside the wire” in order to perform engineering assessments of force protection measures, as well as base expansion. Many of these assessments were able to be conducted remotely, simply by utilizing a topographic UAS to collect geospatial data over the project location while team members remained inside the safety of an established base perimeter.
The 34th FEST-A operated a small, fixed-wing platform capable of covering an entire Forward Operating Base (FOB) in a matter of hours. Smaller commercial-off-the-shelf platforms of this type are autonomous, man portable systems that can land without the need for a runway or extensive operator training. These low-cost systems also require minimal maintenance and spare parts, with most of the maintenance easily able to be performed by the members of the FEST-A team.
Base Master Planning
Due to the expeditionary nature of military infrastructure, the footprint of bases is constantly changing based on operational requirements. This requires base plans to be continuously updated to reflect changes in infrastructure layout and requirements. The high-resolution imagery captured by a UAS allows engineers to update engineering layouts quickly and visually identify what is happening on the ground. A conventional survey data collection of a typical small FOB in Afghanistan would take several days or weeks to complete, while a UAS crew can collect even great fidelity data of the same area in a few hours of flying and data processing.
While larger infrastructure, such as buildings and storage tanks, can be viewed and digitized using satellite imagery (generally around 1-meter resolution), the high-resolution imagery (up to 5-centimeter resolution) collected from a UAS allows engineers to identify smaller infrastructure not available at lower resolutions. Utility features such as electrical panels, power lines, manhole covers, and drainage culverts can be identified and located from the imagery without the need for field collections. The increase in resolution even allows the engineers to determine the types of material and any significant damage done to infrastructure.
Since the imagery is also orthorectified (has a uniform scale), real-world measurements can also be taken directly off the imagery. This becomes especially important when performing engineering designs in congested environments on a base, or avoiding building in areas that have existing utilities.
Utilizing high-percentage image overlap, the UAS is capable of collecting a photogrammetrically-derived 3D point cloud containing elevations of the existing terrain. Each point gives an elevation value every couple of centimeters with a point density of more than 20 points per square meter. Although these point clouds are similar to LiDAR, the UAS does not utilize the active laser sensor found on LiDAR platforms. These point clouds can be converted into 2D representations of topographic data in the form of digital elevation models (DEMs) and contour lines.
One of the most common engineering applications of the topographic data is drainage modeling of bases. The elevation model can determine the direction and flow rate of surface water. This is especially important when collecting information outside of the base perimeter to determine how and where to control the water as it flows on and off a base. Before incorporating the UAS, engineering assumptions with minimal or no data available had to be incorporated into the design of on-base drainage features. By using the UAS topographic data, engineers can ensure that drainage features are properly sized and placed. The high densification of the topographic data (one point every several centimeters) even allows the engineers to determine elevation in narrow drainage features such as ditches or open culverts.
One of the downfalls of the photogrammetrically-derived point cloud collected by the UAS is the inability to penetrate dense overgrowth that is commonly present in drainage ditches. However, conventional topographic survey techniques such as ground-based GNSS can be utilized to fill in the missing data. This is often as simple as taking a couple of survey shots at culverts along a drainage ditch instead of an entire topographic survey. The combination of the UAS and conventional survey techniques allows for the most efficient data collection while still ensuring data quality.
Another application of the topographic data in contingency construction is to determine cut-and-fill quantities for earthwork and existing stockpiles. The UAS topographic data can be easily imported as a surface into computer-aided design (CAD) software, such as AutoCAD Civil 3D in order to give existing ground elevations of a surface. The CAD software can be utilized to make a design surface containing the elevations that depict the cut-and-fill requirements of the site. The software then calculates the volume difference from the existing surface to the design surface. Accurate quantities are crucial when estimating the cost and the construction schedule of a project. The incorporation of the geospatial data produced by the UAS allows for the quantities to be quickly and accurately calculated, utilizing the engineering team’s organic capabilities.
Putting it All Together
The incorporation of UAS increased the capacity of the 34th FEST-A in terms of acceptable size of projects the team was able to undertake. It also allowed the team to accurately conduct assessments of areas which would otherwise require significant security escorts to access safely. This allowed the FEST-A team to operate with just organic personnel in many cases. The team was also able to provide superior support to the warfighter without straining limited security and personnel resources.
As UAS technology continues to evolve, the Army Corps of Engineers will continue to field the most cutting-edge technology available to support its military and civil works missions.