UAV LiDAR vs Photogrammetry
LiDAR-equipped drones mean focus areas such as streams, coastlines, subdividable farm blocks or forest plots can be mapped much more economically and in an environmentally friendly way.
What is LiDAR?
LiDAR, or airborne laser scanning, is an acronym for Light Detection And Ranging. It works by emitting active light pulses from the sensor which reflect back and measurement data is captured. When this happens many thousand times per second the light pulses find gaps in the tree canopy and allow for the generation of a highly detailed digital terrain model (DTM).
How is LiDAR different to photogrammetry?
Photogrammetry by contrast works almost in reverse as it triangulates pixel coordinates from overlapping photos to ‘reverse engineer’ the land cover. While ideal for modelling open construction sites, mines and built environments it doesn’t allow for capturing the ground below grass, scrub or bush.
What is the cost difference between UAV LiDAR and standard drone survey?
The costs are not too dissimilar between UAV LiDAR and a photogrammetric approach as the amount of area captured in a day from each method is fairly similar. The higher upfront investment in the LiDAR system means there is additional overhead recovery, however, this is far outweighed by its ability to capture the topography accurately under vegetation.
The attached image presents a comparison between the UAV LiDAR and photogrammetry flown over the same section of forest. Where the photogrammetry has not been able to map under the trees, the LiDAR survey has achieved thousands of reliable ground strikes from which a detailed terrain model has been formed. The banner image shows the resulting contours, at 1m interval in this case.
The reason using a UAV has proven so effective is the sheer number of LiDAR points that are emitted from the scanner at low altitude. A typical project will see upwards of 1,000 points captured per sqm, resulting in many more ground strikes than manned aircraft surveys.
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