Abstract
The use of unmanned aerial systems (UASs) has rapidly grown in many civil applications since the early 2010s. Nowadays, a large variety of reliable low-cost UAS sensors and controllers are available. However, contrary to ultralight aircrafts (ULAs), UASs have a too small operational range to efficiently cover large areas. Flight regulations prevailing in many countries further reduced this operational range; in particular, the “within visual line of sight” rule. This study presents a new system for image acquisition and high-quality photogrammetry of large scale areas (>10 km²). It was developed by upscaling the UAS paradigm, i.e., low-cost sensors and controllers, little (or no) on-board active stabilization, and adequate structure from motion photogrammetry, to an ULA platform. Because the system is low-cost (good quality-price ratio of UAS technologies), multi-sensors (large variety of available UAS sensors) and versatile (high ULA operational flexibility and more lenient regulation than for other platforms), the possible applications are numerous in miscellaneous research domains. The system was described in detail and illustrated from the flight and images acquisition to the photogrammetric routine. The system was successfully used to acquire high resolution and high quality RGB and multispectral images, and produced precisely georeferenced digital elevation model (DEM) and orthophotomosaics for a forested area of 1200 ha. The system can potentially carry any type of sensors. The system compatibility with any sensor can be tested, in terms of image quality and flight plan, with the proposed method. This study also highlighted a major technical limitation of the low-cost thermal infrared cameras: the too high integration time with respect to the flight speed of most UASs and ULAs. By providing the complete information required for reproducing the system, the authors seek to encourage its implementation in different geographical locations and scientific contexts, as well as, its combination with other sensors, in particular, laser imaging detection and ranging (LiDAR) and hyperspectral.
Highlights
Aerial survey and aerial photogrammetry were primarily developed and used by the military
The system is composed of a flying platform, a ultralight aircrafts (ULAs), and several unmanned aerial systems (UASs) sensors carried by this platform
ground control points (GCPs) were randomly divided into five folds and five optimizations were run
Summary
Aerial survey (the collection of information conducted from airborne vehicles) and aerial photogrammetry (the process of making measurements and maps through the use of aerial photographs) were primarily developed and used by the military. With a MTOW of 5.670 kg [5], light aircrafts are the most used manned vehicle for aerial photogrammetry [1,6,7,8,9,10,11]. Due to their technical characteristics, especially high autonomy and payload, heavy high-resolution cameras with a stabilization mechanism and a powerful processor [10] can be embarked. Helicopters can perform low flight at very low ground speed [17] Their use is very expensive and their flight autonomy is limited
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