Abstract
Traditionally, topographic surveying in earth sciences requires high financial investments, elaborate logistics, complicated training of staff and extensive data processing. Recently, off-the-shelf drones with optical sensors already reduced the costs for obtaining a high-resolution dataset of an Earth surface considerably. Nevertheless, costs and complexity associated with topographic surveying are still high. In 2020, Apple Inc. released the iPad Pro 2020 and the iPhone 12 Pro with novel build-in LiDAR sensors. Here we investigate the basic technical capabilities of the LiDAR sensors and we test the application at a coastal cliff in Denmark. The results are compared to state-of-the-art Structure from Motion Multi-View Stereo (SfM MVS) point clouds. The LiDAR sensors create accurate high-resolution models of small objects with a side length > 10 cm with an absolute accuracy of ± 1 cm. 3D models with the dimensions of up to 130 × 15 × 10 m of a coastal cliff with an absolute accuracy of ± 10 cm are compiled. Overall, the versatility in handling outweighs the range limitations, making the Apple LiDAR devices cost-effective alternatives to established techniques in remote sensing with possible fields of application for a wide range of geo-scientific areas and teaching.
Highlights
In geosciences, terrestrial laser-scanning and airborne laser-scanning (TLS & ALS) techniques are applied for topographic land surveying on a wide range of s cales[1,2,3]
Current high-resolution 3D models based on unmanned aerial vehicles (UAVs) data and Structure-fromMotion Multi-View Stereo (SfM MVS) pipelines are still expensive as they rely on differential global navigation satellite systems (DGNSS), ground control points (GCPs), commercial software and data processing on an external computing d evice[13]
Compared to common Edge Emitting Lasers (EEL), Vertical Cavity Surface Emitting Laser (VCSEL) are convenient for mobile devices, as they can be constructed in small-dimensions featuring a feasible ratio between laser power consumption and supplied power as well as a narrow wavelength bandwidth[28]
Summary
Terrestrial laser-scanning and airborne laser-scanning (TLS & ALS) techniques are applied for topographic land surveying on a wide range of s cales[1,2,3]. The acquisition of a digital terrain model, independent from the scale, requires high capital and logistical costs in the order of several thousand of euros, especially with airborne laser-scanning techniques[6]. Terrestrial laserscanning (TLS) allows the acquisition of digital terrain models up to a medium-scale of a few kilometers with a high temporal and spatial r esolution[8,9]. Terrestrial laser scanners cost at least several thousands of euros, requiring trained operators and line of sight, only allowing a limited number of scanning positions, and are restricted in access to rough terrain. Recent advances in photogrammetry and the availability of lightweight unmanned aerial vehicles (UAVs) offer a potential low-cost alternative to ALS and TLS in order to build 3D surface models with a high temporal and spatial resolution[6,12]. Photo position and orientation cannot be used for satisfactory model registration, making an elaborate model post processing necessary, enabling only experts to use the advantages of smartphone photogrammetry[22]
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