Search

Abstract The small reservoirs in the European montane landscape, which were built in past centuries for various purposes, represent specific cultural and technical heritage but also feature retention potential for mitigating the emerging impacts of climate change, namely, the course of flooding or droughts. However, the frequent lack of technical data on these historical structures, including their storage volume and flooded areas, prevents their consideration in water management planning. In this study, we used unmanned aerial vehicles (UAVs) to produce a detailed 3-D reconstruction of an abandoned montane reservoir that was built for timber flowing in the beginning of 19th century and that has not recently been used for any purpose. The UAV imaging and photogrammetric processing provided an ultra-high-resolution 3-D model of the reservoir basin (5 cm per pixel). Bathymetric analyses were performed based on this basin model to calculate the reservoir volume and flooded area for different water levels. The reliability of the UAV-based model was tested by comparing the results with those of elevation models derived from geodetic field survey using a total station and from conventional data sources based on available aerial LiDAR data. The data were compared to the historical estimates of the reservoir parameters found in the literature. Bathymetric reconstruction of the reservoir properties based on high-resolution UAV data revealed significant retention potential of the structure and historical underestimation of its capacity. The highly detailed UAV-based model helped to eliminate inaccuracies, resulting from the use of the generalized conventional elevation data, that affect the volumetric estimates in the flat topography of the reservoir basin. The study demonstrated the potential applicability of UAV technology for rapid and reliable reconstruction of landscape structures, which is significant for water management. Highlights • UAV imaging, aerial LIDAR data and field survey were used for 3D reconstruction. • High-resolution UAV data eliminated inaccuracies of 3D model in flat topography. • UAV data revealed significant underestimation of the reservoir retention capacity. • UAV technology enables rapid and reliable reconstruction of landscape structures. • Small montane reservoirs can serve for mitigation of hydrometeorological extremes. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

• A single-band unmanned shipborne bathymetric LiDAR. • A two-channel receiving system for improvement of detection ability to the echo signals from water bottom. • The polarized optical systems for suppression of the laser echo energy from the water surface based on the polarization state difference of the laser echo between from water surface and from the water bottom. When a bathymetric LiDAR (Laser Detection And Ranging) onboard unmanned ship is close to the water surface less than 50 cm, the laser echo energy from the water surface is much higher than that from the water bottom. This phenomenon causes a large dynamic range of echo signals that is output from the PMT (Photomultiplier Tube) detector, resulting in that the echo signal from the water bottom cannot correctly be detected in shallow water. For this reason, this paper proposes an optics system to suppress the amplitude of the echo signal from water surface through suppressing the laser echo energy. A two-channel receiving optical system, which receives echo signals from shallow water and deep water is designed and implemented, and then a polarized optical system is designed to embedded inside to suppress the laser echo energy from the water surface. The verifications are carried out through three sets of indoors experiments, and three sets of outdoors experiments. The experimental results demonstrate that the proposed system can effectively suppress 80.7% of the amplitude of the echo signal from the water surface when the voltage control of PMT detector is 0.40 V, which can largely improve the detection ability of the echo signals from water bottom in shallow water. [ABSTRACT FROM AUTHOR]

Abstract: Sea turtles nesting beaches are found near-globally, and the ability to characterize beaches by topographic and bathymetric features has remained largely out of reach. Twenty-one beaches and their offshore areas in southern Florida used by three sea turtle species (Caretta caretta, Chelonia mydas, and Dermochelys coriacea) were compared using topographic measures derived from LiDAR data. Variables such as slope, aspect, rugosity, and topographic and bathymetric position indices (TPI and BPI) were extracted from the LiDAR surface raster to characterize beaches used by sea turtles; stepwise multiple regression was used to determine which variables are most strongly associated with turtle nesting density. The three species exhibited tolerances for similar ranges of values in measured variables; beaches with values outside these tolerances were not used for nesting. Beach nesting density can be successfully modeled for all three species, but different topographic measures were important in each model. This work demonstrates the potential of high spatial resolution topographic datasets to successfully characterize coastal habitat for ecological applications. [Copyright &y& Elsevier]

Abstract: This study evaluates the potential to use waveform data from bathymetric airborne lidar for mapping seabed substratum and vegetation using a site in the Northern Baltic Sea as a study area. One objective of the study was to develop classification procedures including accurate corrections of waveform data for environmental and lidar system factors, to make them useful for mapping areas with variable water quality. Other objectives were to evaluate the classification accuracy using a combination of depth-derived variables and additional waveform variables, and to compare the results with the classification accuracy obtained when classification is performed using depth-derived variables only (without additional waveform variables). The analysis was based on two waveform variables (bottom pulse width and pulse area), in addition to two depth-derived variables (slope and depth standard deviation). The classification was performed using a model-based maximum likelihood approach. The classification models were created and evaluated with lidar data taken from locations documented with underwater video. The results show that inclusion of the waveform variables significantly improved the classification accuracy. Classification of the seabed into three classes (hard substrate; soft substrate with high vegetation; and soft substrate with low vegetation) had an overall accuracy of 86% when evaluated with an independent data set. This highlights the potential of data from airborne lidar, including waveform data (bottom pulse width and pulse area), for mapping shallow seabed habitats in coastal areas. [Copyright &y& Elsevier]

Large areas of the world''s coastal marine environments remain poorly characterized because they have not been mapped with sufficient accuracy and at spatial resolutions high enough to support a wide range of societal needs. Expediting the rate of seafloor mapping requires the collection of multi-use datasets that concurrently address hydrographic charting needs and support decision-making in ecosystem-based management. While active optical and acoustic sensors have previously been compared for the purpose of hydrographic charting, few studies have evaluated the performance and cost effectiveness of these systems for providing benthic habitat maps. Bathymetric and intensity data were collected in shallow water (<50 m depth) coral reef ecosystems using two conventional remote sensing technologies: (1) airborne Light Detection and Ranging (LiDAR), and (2) ship-based multibeam (MBES) Sound Navigation and Ranging (SoNAR). A comparative assessment using a suite of twelve metrics demonstrated that LiDAR and MBES were equally capable of discriminating seafloor topography (r =>0.9), although LiDAR depths were found to be consistently shallower than MBES depths. The intensity datasets were not significantly correlated at a broad 4×5 km spatial scale (r =−0.11), but were moderately correlated in flat areas at a fine 4×500 m spatial scale (r =0.51), indicating that the LiDAR intensity algorithm needs to be improved before LiDAR intensity surfaces can be used for habitat mapping. LiDAR cost 6.6% less than MBES and required 40 fewer hours to map the same study area. MBES provided more detail about the seafloor by fully ensonifying high-relief features, by differentiating between fine and coarse sediments and by collecting data with higher spatial resolutions. Surface fractal dimensions and fast Fourier transformations emerged as useful methods for detecting artifacts in the datasets. Overall, LiDAR provided a more cost effective alternative to MBES for mapping and monitoring shallow water coral reef ecosystems (<50 m depth), although the unique advantages of MBES may make it a more appropriate choice for answering certain ecological or geological questions requiring very high resolution data. [Copyright &y& Elsevier]

Abstract: A nearshore wave, tide and current prediction system was demonstrated during the MREA04 Trial in the Portuguese coastal waters near Pinheiro da Cruz during the early spring of 2004. Daily forecasts of regional scale wave and tidal information and nearshore waves and currents were generated in DIOPS utilizing a suite of regional and nearshore models forced with data from meteorological and oceanographic production centers. A limited beach experiment was conducted with three Nortek current meters deployed in the surf zone and a video imagery system to generate 10-min time exposures used to identify the locations of wave breaking. In this study, Delft3D, a coastal hydrodynamic modeling system, capable of simulating hydrodynamic processes due to waves, tides, rivers, winds and coastal currents, is used to predict the nearshore wave and longshore currents near Pinheiro da Cruz. The nearshore bathymetry used in this study was based on LIDAR data collected in February 2000. Delft3D shows mixed results when compared with the measured wave height and nearshore currents. Improved Delft3D results can be achieved in the future if migrating sand bars can be measured and included in the modeling. [Copyright &y& Elsevier]