Abstract
Abstract. The recent advent of single photon sensitive airborne LiDAR (Light Detection And Ranging) sensors has enabled higher areal coverage performance at the price of an increased outlier rate and a lower ranging accuracy compared to conventional Multi-Photon LiDAR. Single Photon LiDAR, in particular, uses green laser light capable of penetrating clear shallow water. Although primarily designed for large area topographic mapping, the technique can also be used for mapping the water surface and shallow water bathymetry. In this contribution we investigate the capability of Single Photon LiDAR for large area mapping of water surface heights. While interface returns from conventional green-only bathymetric sensors generally suffer from water level underestimation due to the water penetration capabilities of green laser radiation, the specific questions are, if Single Photon LiDAR (i) is less affected by this well known effect due to the high receiver sensitivity and (ii) consequently delivers a higher number of water surface echoes. The topic is addressed empirically in a case study by comparing the water surface responses of Single Photon LiDAR (Navarra, Spain) and Multi-Photon Topo-Bathymetric LiDAR (Neubacher Au, Austria) for selected water bodies with a horizontal water surface (reservoirs, ponds). Although flown at different altitudes, both datasets are well comparable as they exhibit the same strip point density of ca. 14 points/m2. The expected superiority of Single Photon LiDAR over conventional green-only bathymetric LiDAR for mapping water surfaces could not be verified in this investigation. While both datasets show good agreement compared to a reference water level when aggregating points into cells of 10 × 10 m2 (mean deviations < 5 cm), higher resolution Single Photon LiDAR based water surface models (grid size 1–5 m) show a systematic water level underestimation of 5–20 cm. However, independently measured ground truth observations and simultaneous data acquisition of the same area with both techniques are necessary to verify the results.
Highlights
High resolution, area wide mapping of water level heights is important for many fields of application like hydrology, hydraulic engineering, and ecology, but capturing water surfaces is challenging for active or passive remote sensing (Thomas and Guenther, 1990; Rupnik et al, 2015; Mandlburger et al, 2013)
It is noted here that both Single Photon LiDAR and MultiPhoton LiDAR in general and the respective instruments used in this investigation (SPL100, VQ-880-G) in particular provide signal strength information, the investigation at hand entirely focuses on the geometry of the obtained discrete echo point clouds
It can be seen that the Single Photon LiDAR dataset exhibits a considerable number of clutter points above the surface
Summary
Area wide mapping of water level heights is important for many fields of application like hydrology, hydraulic engineering, and ecology, but capturing water surfaces is challenging for active or passive remote sensing (Thomas and Guenther, 1990; Rupnik et al, 2015; Mandlburger et al, 2013). LiDAR operating with very short laser pulses (400 ps) in the visible, green domain of the spectrum (λ=532 nm) for large area water surface mapping. The research questions are, (i) if the single photon sensitivity enables a high density of water surface echoes and (ii) if water surface level underestimation is less compared to conventional LiDAR.
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