How to Get the Most Accurate Aerial Surveys
Drones are quickly finding their way into many services within the industrial sector.
While there is sometimes hesitation to implement new technology, early adopters are often richly rewarded. One such use case has been the utilization of UAVs to conduct aerial surveys.
The art of surveying has been around since people first switched from nomadic hunter-gathers to agriculture-based societies in permanent settlements. As structures were built, people needed to understand the position of objects on the ground accurately.
Drones represent the latest advancement in this field.
While you may be exploring drones for your own survey needs, it’s likely that you have some concerns. That’s understandable.
You might be wondering, “how do drones complete a survey?” And, “are aerial surveys accurate?”
A better understanding of how aerial surveys are conducted, what type of equipment is necessary, and which UAV capabilities are needed for greater accuracy, can help alleviate those concerns.
Let’s break it all down.
How Aerial Surveys Work & How to Prepare For Flight
Drone aerial surveys produce many useful products.
Some of the more common include 2D and 3D orthomosaic maps, 3D models, thermal maps, LiDAR point clouds, and multispectral maps. The process for collecting the raw data needed to produce aerial survey products, such as those listed above, is pretty straightforward.
Before drones take off, the deliverables for the mission must be clearly defined. Determining which products (3D models, 2D orthomosaics, etc.) need to be produced is essential for the planning process.
Investigation
Once those deliverables are identified, it’s a important to investigate the site.
Before drone use became an option, aerial survey teams would often work in dangerous areas, such as active construction sites or treacherous terrain. While using drones significantly reduces that risk, you’ll still want to conduct a thorough site investigation to ensure a safe working environment.
In order to achieve a high level of accuracy, you’ll want to use Ground Control Points (GCPs), or other similar precision location identification tools. We’ll discuss these in a bit, but your site investigation should help you select the best locations for each GCP and/or base station.
Planning
Next, plan out your mission.
The drone’s flight path, camera angles used to collect data, and the amount of overlap in images is determined and set into the flight plan. Once loaded, the mission is flown, and the first half of the aerial survey process is complete.
Processing
The second half encompasses the processing of the data collected by the drone.
When using precision survey tools (GCPs, RTK, PPK), the drone becomes part of a Position & Orientation System (POS). The images collected are each given reference points on the ground.
When the images are matched up with the highly accurate data from GCPs/RTK or PPK, an accurate survey is collected.
The accuracy level depends on all the equipment used in the remote pilot’s UAV system.
In 2019, DroneDeploy, a leading app for drone surveys, independently tested a DJI Phantom 4 RTK and achieved 2cm relative vertical accuracy and 1.20 cm relative horizontal accuracy. With precision, RTK and PPK or specialized GCPs, such as those manufactured by Propeller Aero, survey level accuracy is attainable.
GCPs, RTK, and PPK
GCPs used in combination with RTK or using PPK are the key to getting survey-level accuracy from a drone.
Here’s a brief introduction of each asset:
Ground Control Points (GCPs) are points on the earth’s surface of known location used to geo-reference Landsat Level-1 imagery.
Typically, these points are squares placed around the ground of the survey area. As these are known, surveyed points, they can be used to align the images collected by the drone with locations on the surface.
Real-Time Kinematic (RTK) is a tool that uses range-based measurements to make corrections to the GPS location recorded by the drone.
A drone with GPS alone cannot provide survey-level accuracy. Range measurements essentially recalibrate the data of the GPS to give the exact location for each image collected.
Post-Processing Kinematic (PPK) is another method for correcting GPS location errors that allow for survey-level accuracy.
Flights typically take more time if you’re using PPK, as is the post-processing of data once the mission is complete. PPK does not need a radio link between the drone and the base station to work, nor does it need GCPs.
So, if you need survey-level measurements with a drone, you will either need to use RTK and GCPs (which corrects during the flight) or PPK (correcting in the cloud post flight) to obtain that level of accuracy need.
Bringing It All Together
The surveying needs of industry will become more complex over time.
Drones offer a highly efficient, cost-effective solution for providing accurate survey products to meet those needs.
Are you looking to conduct aerial surveys with drones on your own? You’ll need training and consultation.
Are you looking to hire a company to produce the data for you? You’ll want an experienced remote pilot with a proven track record.
At Consortiq, we offer the full solution. We’ll help you build internal drone programs and train your pilots. Or, we’ll do the work for you, either independently or alongside your team.
With drones, there’s always a better way, and it’s our goal to help you find it! With hubs in North America and Europe, we’ll come to you, wherever you are in the world!
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David Daly - Contributing Author
David Daly, is an award-winning photographer/writer and licensed (FAA) Commercial sUAS pilot. A graduate of the United States Naval Academy, David is a former Marine Corps officer with a BS in Oceanography and has earned his MBA from the University of Redlands. David has worked for Fortune 100 companies and has a background in aerospace, construction, military/defense, real estate, and technology.
