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!

Schedule your risk-free consultation by completing the form below.

David Daly - Contributing Author

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.

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LiDAR and How It’s Used With Drones

When it comes to UAV payloads, thermal and Red Green Blue (RGB) cameras get a great deal of attention.

With low price points, the technology is easily accessible to just about everyone. Several standard drone missions, such as three-dimensional mapping, are effortlessly carried out using it. There are, however, limitations to using only these two types of payloads on drones.

Thermal cameras are ideally suited for inspections where temperature variations are the primary data points. Beyond this function they are, by design, limited.

RGB cameras are excellent tools for photogrammetry. While this survey method is accurate and useful in a wide range of applications, it is also not without its limitations. For example, drones with RGB cameras can survey vacant land in preparation for development. In most cases, the images collected can produce precise three-dimensional models and topographic maps that planners will find useful.

However, if this same land were covered in thick, dense vegetation, the RGB camera would fail to give planners any information on the actual earth’s surface. For this type of analysis, RGB and thermal cameras are not the best tools for the job.

What is LiDAR and how does it work?

Invented in 1961 by the Hughes Aircraft Company, LiDAR (Light Detection and Ranging) is ideal for the type of analysis mentioned above. LiDAR systems consist primarily of three components: a laser, scanner, and a specialized GPS receiver.

LiDAR works by accurately measuring the distance from the drone to the ground. A laser is fired millions of times from the LiDAR scanner towards the ground as the drone flies a predetermined pattern. As each pulse of light is emitted, the exact time the light is fired is recorded. As the light pulse is reflected, the scanner detects the return and again marks the exact time the light returned.

The specialized GPS receiver records the exact position of the sensor throughout this process. An equation that utilizes the constant speed of light generates a slant range for each beam of light fired. When all the data is compiled, millions of points on the ground produce an accurate representation of the earth’s surface and features above it.

The data points are so numerous and so precise that layers of vegetation or other obstacles can be removed to show the topography of the region. One light pulse can generate multiple returns and thus, layer the area being surveyed. The technology has seen successful use in many fields such as disaster response, high precision infrastructure monitoring, and topographic/hydrographic survey.

 

Types of LiDAR for UAS, and the industries that benefit

UAVs use two types of lidar.

For measuring the earth’s surface, topographic LiDAR is ideal. It utilizes a near-infrared laser for mapping land.

The second type — bathymetric LiDAR — is designed for surveying the seafloor and riverbeds. It uses a green laser to penetrate water, but operates on the same principles as described above.

LiDAR systems on UAS provide professionals across many industries the ability to map the earth’s most challenging environments. The level of accuracy spread across millions of data points is particularly beneficial to construction planners, as well as those monitoring utility infrastructures. Hard-to-see features, such as powerlines, are easily identified by LiDAR. These features can also be isolated from other features, aiding in in-depth analysis.

There is perhaps a no better example of the power of LiDAR than in archeology. The incredibly dense jungles of Central America were home to one of the ancient world’s greatest civilizations, the Mayan. The Mayans built vast cities with massive structures. 

After a mysterious decline and disappearance in 900 A. D., many of their cities were swallowed up by the jungle. Dense jungle canopies all but erased many locations. Traditional investigation methods, such as aerial surveys in aircraft, see only vast expanses of the jungle.

However, LiDAR systems on crewed aircraft and drones are revolutionizing what researchers know about the Mayans. LiDAR can remove the vegetation and show what lies underneath. In some cases, its identified previously unknown locations with tens of thousands of structures. LiDAR is helping to expand this ancient civilization’s study in ways that seemed unimaginable just a few years ago.

Bringing it all together

Drones carrying LiDAR payloads are a power tool.

With only a few years of UAV technology and lidar working together, impossible topographic challenges are becoming increasingly simple tasks. For decision makers in construction, utilities, survey, and research, the advantages of UAVs carrying LiDAR are worth further investigation.

Want to know which drone platform works best for your project? Need help with gathering unmanned data or policy development? We’re here to help! 

Complete the form below to get started!

David Daly - Contributing Author

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.

Ready to Integrate Drones Into Your Organization? Contact Us Today to Get Started!

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