scholarly journals MAPPING OF WATER SURFACE LEVELS AND SLOPES WITH SINGLE PHOTON LIDAR – A CASE STUDY AT THE RIVER RHINE

2020 ◽  
Vol XLIII-B1-2020 ◽  
pp. 57-64
Author(s):  
G. Mandlburger ◽  
R. Weiß ◽  
T. Artz
Keyword(s):  
High Resolution ◽  
Water Surface ◽  
Point Cloud ◽  
Single Photon ◽  
Numerical Models ◽  
River Rhine ◽  
Surface Mapping ◽  
Federal Institute ◽  
Precise Knowledge ◽  
Pulse Density

Abstract. Precise knowledge of water surface level heights is crucial for safe ship navigation and as basis for calibration of hydrodynamic-numerical models. While Airborne Laser Scanning (ALS) is a well established technique for topographic mapping, ALS-based water surface mapping using conventional infrared lasers suffers from the high degree of specular reflection which leads to data voids for off-nadir angles beyond 5–7 degrees. The advent of single photon sensitive ALS systems using green laser sources presents the prospect of large-area, high-resolution water surface mapping due to the high receiver sensitivity and measurement rate of such systems. Building on previous studies on subject matters, we present the results of a pilot project initiated and conducted by the German Federal Institute of Hydrology (BfG, Koblenz) at the Rhine River. Three specific test sites with varying water surface and flow velocity properties were captured on October 30th and 31th, 2019 with the Leica SPL100 from flying altitudes of 3000 m, 2500 m, 1600 m, and 800 m, respectively. As anticipated, the water surface laser pulse density was high and exhibited 20–145 points/m2 depending on flying altitude. After quality control, strip adjustment, and point cloud analysis, three water surface classification methods were implemented based on: (i) height quantiles, (ii) point cloud segmentation, and (iii) inverse DTM filtering. All approaches featured relative and absolute water level height accuracies better than 10 cm. We conclude that Single Photon LiDAR based high resolution mapping of water surface levels and tilts is feasible when employing application specific data acquisition parameters, i.e., off-nadir angle ≤10° and flying altitude ≤3000 m.

scholarly journals On the Feasibility of Water Surface Mapping with Single Photon LiDAR

2019 ◽  
Vol 8 (4) ◽  
pp. 188 ◽  
Author(s):  
Gottfried Mandlburger ◽  
Boris Jutzi
Keyword(s):  
High Resolution ◽  
Water Level ◽  
Water Surface ◽  
Laser Light ◽  
Single Photon ◽  
Green Laser ◽  
Sensor Technology ◽  
Large Area ◽  
Surface Mapping ◽  
Surface Models

Single photon sensitive airborne Light Detection And Ranging (LiDAR) enables a higher area 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 potentially capable of penetrating clear shallow water. The technology is designed for large-area topographic mapping, which also includes the water surface. While the penetration capabilities of green lasers generally lead to underestimation of the water level heights, we specifically focus on the questions of whether Single Photon LiDAR (i) is less affected in this respect due to the high receiver sensitivity, and (ii) consequently delivers sufficient water surface echoes for precise high-resolution water surface reconstruction. After a review of the underlying sensor technology and the interaction of green laser light with water, we address the topic by comparing the surface responses of actual Single Photon LiDAR and Multi-Photon Topo-Bathymetric LiDAR datasets for selected horizontal water surfaces. The anticipated superiority of Single Photon LiDAR could not be verified in this study. While the mean deviations from a reference water level are less than 5 cm for surface models with a cell size of 10 m, systematic water level underestimation of 5–20 cm was observed for high-resolution Single Photon LiDAR based water surface models with cell sizes of 1–5 m. Theoretical photon counts obtained from simulations based on the laser-radar equation support the experimental data evaluation results and furthermore confirm the feasibility of Single Photon LiDAR based high-resolution water surface mapping when adopting specifically tailored flight mission parameters.

scholarly journals FEASIBILITY INVESTIGATION ON SINGLE PHOTON LIDAR BASED WATER SURFACE MAPPING

2018 ◽  
Vol IV-1 ◽  
pp. 109-116
Author(s):  
G. Mandlburger ◽  
B. Jutzi
Keyword(s):  
Shallow Water ◽  
Water Level ◽  
Water Surface ◽  
Single Photon ◽  
Ground Truth ◽  
Green Laser ◽  
Airborne Lidar ◽  
Large Area ◽  
Surface Mapping

<p><strong>Abstract.</strong> 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<span class="thinspace"></span>points/m<sup>2</sup>. 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<span class="thinspace"></span>&amp;times;<span class="thinspace"></span>10<span class="thinspace"></span>m<sup>2</sup> (mean deviations &amp;lt;<span class="thinspace"></span>5<span class="thinspace"></span>cm), higher resolution Single Photon LiDAR based water surface models (grid size 1&amp;ndash;5<span class="thinspace"></span>m) show a systematic water level underestimation of 5&amp;ndash;20<span class="thinspace"></span>cm. However, independently measured ground truth observations and simultaneous data acquisition of the same area with both techniques are necessary to verify the results.</p>

Experimental study of resonant shallow flows past a lateral cavity: a benchmark test for high-resolution numerical models

2020 ◽  
Author(s):  
Sergio Martínez Aranda ◽  
Adrián Navas-Montilla ◽  
Antonio Lozano ◽  
Pilar García-Navarro
Keyword(s):  
Experimental Study ◽  
High Resolution ◽  
Water Resources ◽  
Water Surface ◽  
Numerical Models ◽  
Resonance Phenomenon ◽  
Data Set ◽  
River Bank ◽  
Shallow Flows ◽  
Lateral Cavity

&lt;p&gt;&lt;span&gt;The study of resonant shallow flows past a lateral cavity is of great relevance due to their interest in civil and environmental engineering [1]. Such flows exhibit the presence of a standing gravity wave, called seiche, which is coupled with the shedding of vortices at the opening of the cavity. A complete understanding of such phenomenon is necessary as it may determine the mass exchange between the main channel and the cavity [2]. &lt;/span&gt;&lt;span&gt;A better insight into this phenomenon helps to improve the design and implementation of innovative river bank restoration techniques&lt;/span&gt;&lt;span&gt;. An experimental study of the resonant flow in a laboratory flume with a single lateral cavity is herein presented. Five different flow configurations at a fixed Froude number (Fr=0.8) are considered. The main novelty of the present work is the use of a pioneering non-intrusive experimental technique [3] to measure the water surface at the channel-cavity region. This optical technique offers high resolution 2D data in time and space of the water surface evolution, allowing to determine the relevant features of the seiche oscillation, i.e. spatial distribution of oscillation nodes and anti-nodes, oscillation modes and amplitude of the oscillation. Such data are supplemented with Particle Image Velocimetry measurements to perform a more detailed study of the resonance phenomenon. High-resolution two-dimensional amplitude oscillation maps of the seiche phenomenon are presented for the experimental water depth. Experimental velocity fields inside the cavity are presented and confirm the inherent coupling between the unstable shear layer at the opening of the cavity and the gravity standing wave. The high quality of the experimental data reported in this work makes this data set a suitable benchmark for numerical simulation models in order to evaluate their performance in the resolution of turbulent resonant shallow flows.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;[1] C. Juez, M. Thalmann, A. J. Schleiss &amp; M. J. Franca, Morphological resilience to flow fluctuations of fine sediment deposits in bank lateral cavities, Advances in Water Resources, 115 (2018) 44-59.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;[2] I. Kimura &amp; T. Hosoda, Fundamental properties of flows in open channels with dead zone, Journal of Hydraulic Engineering 123 (1997) 98-107.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;[3] S. Mart&amp;#237;nez-Aranda, J. Fern&amp;#225;ndez-Pato, D. Caviedes-Voulli&amp;#232;me, I. Garc&amp;#237;a-Palac&amp;#237;n &amp; P. Garc&amp;#237;a-Navarro, Towards transient experimental water surfaces: a new benchmark dataset for 2D shallow water solvers, Advances in water resources, 121 (2018) 130-149.&lt;/span&gt;&lt;/p&gt;

scholarly journals Probing Be star disks: new insights from Hα spectroscopy and detailed numerical models

2010 ◽  
Vol 6 (S272) ◽  
pp. 398-399 ◽  
Author(s):  
Carol E. Jones ◽  
Christopher Tycner ◽  
Jessie Silaj ◽  
Ashly Smith ◽  
T. A. Aaron Sigut
Keyword(s):  
High Resolution ◽  
Numerical Models ◽  
Analytical Tool ◽  
High Resolution Spectroscopy ◽  
Be Stars ◽  
Line Shapes ◽  
Physical Conditions ◽  
Temperature Distributions ◽  
Inclination Angles ◽  
Be Star

AbstractHα high resolution spectroscopy combined with detailed numerical models is used to probe the physical conditions, such as density, temperature, and velocity of Be star disks. Models have been constructed for Be stars over a range in spectral types and inclination angles. We find that a variety of line shapes can be obtained by keeping the inclination fixed and changing density alone. This is due to the fact that our models account for disk temperature distributions self-consistently from the requirement of radiative equilibrium. A new analytical tool, called the variability ratio, was developed to identify emission-line stars at particular stages of variability. It is used in this work to quantify changes in the Hα equivalent widths for our observed spectra.

Splash formation by spherical drops

2001 ◽  
Vol 427 ◽  
pp. 73-105 ◽  
Author(s):  
LIOW JONG LENG
Keyword(s):  
High Resolution ◽  
Quantitative Data ◽  
Water Surface ◽  
High Speed ◽  
Scaling Laws ◽  
Capillary Wave ◽  
Water Drop ◽  
Qualitative And Quantitative ◽  
High Resolution Images ◽  
The Impact

The impact of a spherical water drop onto a water surface has been studied experimentally with the aid of a 35 mm drum camera giving high-resolution images that provided qualitative and quantitative data on the phenomena. Scaling laws for the time to reach maximum cavity sizes have been derived and provide a good fit to the experimental results. Transitions between the regimes for coalescence-only, the formation of a high-speed jet and bubble entrapment have been delineated. The high-speed jet was found to occur without bubble entrapment. This was caused by the rapid retraction of the trough formed by a capillary wave converging to the centre of the cavity base. The converging capillary wave has a profile similar to a Crapper wave. A plot showing the different regimes of cavity and impact drop behaviour in the Weber–Froude number-plane has been constructed for Fr and We less than 1000.

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