Geodetic imaging with airborne LiDAR: the Earth's surface revealed

Abstract

The past decade has seen an explosive increase in the number of peer reviewed papers reporting new scientific findings in geomorphology (including fans, channels, floodplains and landscape evolution), geologic mapping, tectonics and faulting, coastal processes, lava flows, hydrology (especially snow and runoff routing), glaciers and geo-archaeology. A common genesis of such findings is often newly available decimeter resolution 'bare Earth' geodetic images, derived from airborne laser swath mapping, a.k.a. airborne LiDAR, observations. In this paper we trace nearly a half century of advances in geodetic science made possible by space age technology, such as the invention of short-pulse-length high-pulse-rate lasers, solid state inertial measurement units, chip-based high speed electronics and the GPS satellite navigation system, that today make it possible to map hundreds of square kilometers of terrain in hours, even in areas covered with dense vegetation or shallow water. To illustrate the impact of the LiDAR observations we present examples of geodetic images that are not only stunning to the eye, but help researchers to develop quantitative models explaining how terrain evolved to its present form, and how it will likely change with time. Airborne LiDAR technology continues to develop quickly, promising ever more scientific discoveries in the years ahead.

Airborne radiation mapping: overview and application of current and future aerial systems

“…The effect of diffusive scattering is also not a significant limitation; the low altitude of the flight intercepts the scattered region early compared to higher altitudes. In reality, the roughness of the ground and the influence of topography will produce more secular and diffusive scattering than the flat Lambertian surface shown in Figure 5, however, the results are unlikely to be affected strongly by this as the signal strength is large at emission, hence a large proportion still returns to the detector (Glennie et al 2013).…”

“…Lidar is defined as an 'optics remote sensing technology that measures properties of scattered and reflected light to find range and/or other information about a distant target' (Karp and Stotts 2012). Modern systems use the 'time of flight' method ( Figure 5) to measure the distance to the target surface (Glennie et al 2013;Karp and Stotts 2012;Stefanik et al 2013). There are two variations of the technology to consider for radiation mapping applications: (i) single point range finders and (ii) 3D scanning systems.…”

“…A 3D scanning system works in a similar way, but uses a beam dispersal attachment (often an oscillating block or rotating mirror) to divert the emitted beams in multiple directions to create a 'beam swathe' (Figure 5). Using this swathe combined with the physical movement of the system across a target area, a 3D point cloud can be produced, which can be processed into a 3D representation of the area (Glennie et al 2013;Stefanik et al 2013). The length of the laser pulses in both variations produces a minimum length for the observation beam; causing issues with overlapping reflections at distances smaller than the beam length.…”

“…The length of the laser pulses in both variations produces a minimum length for the observation beam; causing issues with overlapping reflections at distances smaller than the beam length. For example, the situation described in the article by Glennie et al (2013) details that a 10 ns pulse duration corresponds to a 3 m path length, hence a target within this range will be poorly represented.…”

“…water and other gaseous molecules within air) as well as diffuse and secular scattering from reflective surfaces (Figure 5), these former factors act to attenuate the strength of the returning signal. The electrical systems of the computer can distinguish the signals using the leading edge detection of the returning beam relative to the incident (Glennie et al 2013;Karp and Stotts 2012). Edge detection is the algorithm used by the system to detect the returning signal by looking for sharp changes in the signal characteristics received by the sensor relative to the background.…”