Read Time 10 mins
18/04/2023
Introduction
Elevation models play a vital role in understanding the Earth's terrain and are indispensable tools in various industries. Among the different types of elevation models, Digital Elevation Models (DEM) and Digital Surface Models (DSM) stand out due to their widespread use and diverse applications. These models are essential for tasks such as flood risk assessment, infrastructure planning, and environmental management, among others.
In recent years, the use of drones or Unmanned Aerial Vehicles (UAVs) has revolutionised the way elevation data is captured. Drones offer numerous advantages over traditional methods, including cost-effectiveness, speed, and the ability to access remote or difficult-to-reach areas. This blog post will delve into the world of elevation models, specifically DEMs and DSMs, and explore the growing role of drones in capturing elevation data to create accurate and detailed models.
Understanding Elevation Models: DEM & DSM
Digital Elevation Models (DEMs)
Definition and purpose Digital Elevation Models (DEMs) are a type of elevation model that represents the Earth's terrain in a continuous and digital format. DEMs are created by sampling elevation data at regular intervals, creating a grid or raster of elevation points. The primary purpose of DEMs is to provide accurate representations of the Earth's bare ground surface, with all natural and man-made features removed.
Applications
Hydrology: DEMs play a crucial role in hydrological modelling and analysis, including watershed delineation, flow direction, and floodplain mapping. Accurate elevation data is essential for predicting how water will flow and accumulate during floods or heavy rainfall events.
Geology: In the field of geology, DEMs are used to study landforms, analyse geomorphological processes, and assess landslide hazards. Elevation data helps geologists identify patterns and structures in the Earth's surface, which can offer insights into the underlying geological processes.
Infrastructure planning: DEMs are essential tools for planning and designing infrastructure projects such as roads, bridges, and dams. Engineers use elevation data to optimise routes, assess terrain stability, and estimate construction costs.
Environmental management: Environmental management relies heavily on DEMs for tasks such as habitat modelling, erosion control, and natural disaster mitigation. Accurate elevation data helps identify vulnerable areas, monitor land use changes, and plan effective conservation strategies.
Digital Surface Models (DSMs)
Definition and purpose Digital Surface Models (DSMs) represent the Earth's surface, including all natural and man-made features such as buildings, trees, and other infrastructure. Unlike DEMs, DSMs provide a complete picture of the Earth's surface, making them valuable for applications that require detailed information on surface features.
Applications
Urban planning: DSMs are extensively used in urban planning to analyse land use, model urban growth, and assess the impact of new developments. High-resolution DSMs can provide detailed information on building heights and densities, aiding in the decision-making process for urban planners.
Forestry: In forestry management, DSMs help estimate biomass, monitor deforestation, and assess the health of forests. By comparing DSMs over time, forestry professionals can detect changes in forest cover and track the success of conservation efforts.
Telecommunications: DSMs play a vital role in the design and optimisation of telecommunication networks. By accounting for the impact of terrain and surface features on signal propagation, DSMs enable more accurate predictions of network coverage and performance.
3D mapping and visualisation: DSMs are widely used in creating realistic 3D maps and visualisations for various industries, including entertainment, tourism, and real estate. By incorporating surface features, DSMs offer a more accurate and immersive representation of the real world.
The Role of Drones in Capturing Elevation Data
Advantages of using drones
Cost-effectiveness: Drones have emerged as a cost-effective alternative to traditional data capture methods such as manned aircraft and ground-based surveys. By reducing labour costs, minimising the need for expensive equipment, and streamlining data processing, drones significantly lower the overall cost of capturing elevation data.
Speed and efficiency: Drones can cover large areas quickly, significantly reducing the time required for data collection. In addition, drones can capture data at any time of day and under various weather conditions, ensuring that projects stay on schedule.
Flexibility and ease of deployment: Drones can be easily deployed in diverse environments, from urban areas to remote and hard-to-reach locations. Their compact size and manoeuvrability enable them to access areas that may be challenging or impossible for traditional methods, allowing for more comprehensive and accurate data collection.
High-resolution data: Drone-based elevation data capture methods, such as photogrammetry and LiDAR, can generate high-resolution data with sub-meter accuracy. This level of detail is essential for creating accurate and detailed DEMs and DSMs that can be used for a wide range of applications.
Types of drone sensors for elevation data capture
Photogrammetry: Photogrammetry is a technique that involves capturing overlapping images of the Earth's surface and using specialised software to process and stitch these images into a 3D model. Drone-based photogrammetry systems typically include high-resolution cameras and GPS units, enabling the capture of georeferenced images that can be used to create accurate DEMs and DSMs.
LiDAR: LiDAR (Light Detection and Ranging) is a remote sensing technology that uses lasers to measure the distance between the sensor and the Earth's surface. By emitting laser pulses and measuring the time it takes for the light to reflect back, LiDAR systems can generate highly accurate elevation data. Drone-mounted LiDAR systems offer the advantage of capturing data at low altitudes and with high point density, resulting in highly detailed and accurate elevation models.
Creating DEMs and DSMs with Drone Data
Photogrammetry-based method
Overview and process
The photogrammetry-based method involves capturing overlapping aerial images of the Earth's surface using a drone-mounted camera. These images are then processed using specialised software that identifies common points in the overlapping images and calculates the 3D coordinates of these points. The resulting 3D point cloud is used to generate a Digital Elevation Model (DEM) or Digital Surface Model (DSM), depending on the application.
Software solutions
Various software solutions are available for processing drone-captured images and generating DEMs and DSMs. Some popular photogrammetry software options include Pix4D, Agisoft Metashape, and Autodesk ReCap. These programs offer a range of tools and features to optimise the quality and accuracy of the elevation models generated.
Accuracy and limitations
Photogrammetry-based methods can produce high-resolution DEMs and DSMs with sub-meter accuracy. However, the accuracy of the resulting models depends on several factors, such as image quality, camera calibration, and the accuracy of the GPS data. Additionally, photogrammetry may struggle to accurately capture elevation data in areas with dense vegetation or complex terrain, as the overlapping images may not provide a clear view of the ground surface.
LiDAR-based method
Overview and process
The LiDAR-based method involves mounting a LiDAR sensor on a drone and flying it over the area of interest. The sensor emits laser pulses that bounce off the Earth's surface and return to the sensor. By measuring the time it takes for the pulses to return, the LiDAR system calculates the distance between the sensor and the surface, generating a highly accurate 3D point cloud. This point cloud is then processed to create a DEM or DSM, depending on the application.
Software solutions
There are several software solutions available for processing drone-captured LiDAR data and generating DEMs and DSMs. Popular options include LAStools, Global Mapper, and TerraSolid. These programs offer various tools for processing, filtering, and analysing LiDAR point clouds to generate accurate and detailed elevation models.
Accuracy and limitations
LiDAR-based methods can produce extremely accurate elevation data, often with centimeter-level precision. Unlike photogrammetry, LiDAR can penetrate vegetation and accurately capture the ground surface beneath. However, LiDAR systems can be more expensive and require specialised expertise to operate and process the data. Additionally, LiDAR data capture may be affected by environmental factors such as atmospheric conditions and the presence of water, which can influence the accuracy of the resulting elevation models.
Real-World Applications and Case Studies
Flood modelling and risk assessment
DEMs and DSMs generated using drone-captured data have been extensively used in flood modelling and risk assessment. Accurate elevation models are critical for predicting flood extents and identifying vulnerable areas, allowing governments and communities to prepare for and mitigate the impact of floods. In a case study from the Netherlands, researchers used drone-captured data to create detailed DEMs and DSMs, which were then used to model various flood scenarios and develop appropriate flood risk management strategies.
Infrastructure and construction monitoring
Drone-captured elevation data has become an essential tool for monitoring infrastructure and construction projects. By creating DEMs and DSMs, engineers and project managers can track progress, identify potential issues, and ensure that projects are completed on time and within budget. A case study in Malaysia involved using drone-captured data to create DEMs and DSMs for a large-scale infrastructure project, allowing engineers to monitor earthworks, plan construction activities, and optimise resource allocation more effectively.
Agricultural and forestry management
Drones equipped with photogrammetry or LiDAR sensors have become invaluable for agricultural and forestry management applications. In a case study from Brazil, researchers used drone-captured data to create detailed DSMs that helped assess the health and productivity of a eucalyptus plantation. The resulting DSMs allowed forestry professionals to monitor tree growth, estimate biomass, and make informed decisions about plantation management.
Archaeological site documentation
Drone-based elevation models have proven invaluable for the documentation and analysis of archaeological sites. High-resolution DEMs and DSMs allow archaeologists to identify and study subtle landscape features, such as ancient earthworks or buried structures, that may be difficult or impossible to detect using traditional ground-based methods. In a case study from Italy, researchers used drone-captured data to create detailed elevation models of an archaeological site, revealing previously undiscovered features and providing a comprehensive record of the site for future study and preservation efforts.
Conclusion
Digital Elevation Models (DEMs) and Digital Surface Models (DSMs) play a crucial role in various industries, from urban planning and infrastructure development to environmental management and archaeology. The accurate representation of the Earth's terrain provided by these models allows professionals to make informed decisions, optimise resources, and better understand the world around us.
The use of drones for capturing elevation data has revolutionised the field, offering numerous advantages over traditional methods. Drones provide a cost-effective, fast, and flexible solution for capturing high-resolution elevation data in a wide range of environments. The use of photogrammetry and LiDAR sensors on drones has opened up new possibilities for creating detailed and accurate DEMs and DSMs.
As drone technology continues to advance, there is significant potential for further exploration and development of drone-based elevation modelling techniques. By embracing this technology and pushing the boundaries of what is possible, professionals across various industries can unlock new insights, improve decision-making, and contribute to a better understanding of our world.