Jul 2026· The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences· Vol XLIX-B2-2026, pp. 939-946· 0 citations· 12 references
Abstract
Abstract. Airborne laser bathymetry (ALB) is an efficient and accurate tool for mapping submerged environments, particularly shallow water bodies that are difficult to access with surface vessels. Modern ALB systems can achieve accuracies comparable to SONAR. However, multiple factors, including geo-referencing, water surface modelling, and range measurements, influence the resulting point cloud, making analytical error propagation challenging. Empirical evaluation against reference data is therefore essential, but difficult: ALB accuracy is typically in the low centimetre range, requiring reference data of equal or higher accuracy. Robotic total stations enable acquisition of underwater reference data for shallow water depths, e.g., up to 4.5m, with expected accuracies between 3mm to 10mm, depending on water depth, which approaches the inherent accuracy of ALB and limits the evaluation significance. In this study, we assess a UAS-based ALB data set from a mountain lake in Austria using reference planes and points acquired by robotic total stations. We separate the accuracy analysis into trueness and precision to isolate the effects of geo-referencing and water surface modelling from the intrinsic uncertainty of the LiDAR sensor. The results show that geo-referencing introduces the largest systematic bias, while the precision of the ALB data remains approximately 1 cm to 2 cm, even for submerged measurements. These findings demonstrate the high accuracy of state-of-the-art ALB systems and provide a framework for rigorous accuracy assessment in shallow aquatic environments.
Abstract. This study empirically evaluates the geometric accuracy of point cloud data acquired using an underwater lidar (ULi) system in a tropical shallow water environment. The field test was conducted in the tropical waters of the Seribu Islands, Indonesia, characterised by relatively low turbidity. Terrestrial laser scanning (TLS) and close-range photogrammetry were employed as independent reference datasets. Geometric discrepancies between datasets were quantified using the multiscale model-to-model cloud comparison (M3C2) algorithm, and errors were statistically characterised using the median and median absolute deviation (MAD) to ensure robustness under non-normal distributions. The results indicate that the error of ULi relative to TLS is 0.008 ± 0.012 m, while the error relative to photogrammetry is 0.006 ± 0.013 m. In comparison, the discrepancy between photogrammetry and TLS is smaller, at 0.002 ± 0.004 m. Dimensional analysis of an acoustic Doppler current profiler (ADCP) frame further shows that ULi agrees with TLS and photogrammetry within the millimetre to centimetre range (0.000–0.015 m). Larger deviations in specific segments are attributed to local effects, including edge-related artefacts. Overall, the results demonstrate that ULi provides reliable geometric measurements in shallow-water conditions with low turbidity. Despite slightly lower accuracy compared to terrestrial methods, the system shows potential for underwater mapping applications, particularly in shallow water environments.
Mentari K. Azzahra, F. Muhammad, Arnadi Murtiyoso et al.· The International Archives o...· 0 citations
Abstract. Bathymetric Laser Scanning (BLS) enables high-resolution mapping of underwater topography using green-wavelength laser pulses that penetrate the water column. However, precise georeferencing of the BLS data is affected by refraction at the air–water interface, which displaces submerged features and affects conventional strip adjustment methods. This paper introduces an integrated refraction-aware georeferencing workflow that combines refraction correction with trajectory and boresight optimization within a unified adjustment framework. Implemented using the scientific OPALS laser scanning software, the workflow starts with direct georeferencing of uncorrected laser returns, derives a water surface model, applies Snell’s law-based refraction correction, and performs iterative strip adjustment until convergence. The approach was validated using UAV-borne topo-bathymetric LiDAR data from Lake Alm (Almsee) in Upper Austria, captured with a RIEGL VQ-840-GE sensor system. Comparative analysis across multiple processing scenarios demonstrates that the proposed integrated method significantly improves internal consistency between overlapping flight strips. The residual height discrepancies, quantified by the median absolute deviation (σMAD), were reduced from 4.5 cm using standard processing workflows to 2.1 cm with the integrated approach — an improvement exceeding 50%. A single processing pass was sufficient for the relatively calm conditions of the test site, though iterative refinement may benefit more dynamic water surfaces. The presented methodology is generic and can be embedded in any laser scanning framework supporting modular georeferencing and refraction correction.
Gottfried Mandlburger, Lucas Dammert, Jan Rhomberg-Kauert et al.· The International Archives o...· 0 citations
Abstract. This work presents a robust calibration framework for marine LiDAR systems by leveraging spherical targets to jointly estimate boresight angles and lever arm offsets. The use of spheres provides a geometrically consistent and orientation-independent reference, enabling accurate calibration even in complex marine environments. To evaluate the proposed approach, a synthetic data generation algorithm was developed to simulate LiDAR scans over spherical targets, allowing controlled experiments across a wide range of sensor configurations. Furthermore, the calibration method was validated using real LiDAR data collected from a hydrographic survey vessel. Due to the calibration, the distance between the surveyed spherical centers and their estimated center positions from LiDAR point clouds is minimised to an RMS error of 0.036 m, which is within the range of the accuracy of the POS MV navigation system. We finally introduce a low cost in-house mobile LiDAR system integrating similar sensors in the ROS environment in order to address the challenges of obtaining LiDAR data in varying environmental conditions.
Jordan McManus, C. Larouche, M. H. Shahraji· The International Archives o...· 0 citations
Abstract. Green-wavelength LiDAR systems enable high-resolution 3D sensing in underwater environments, but the geometric evaluation of measurements acquired across the waterline remains challenging. This is mainly because traceable reference instruments typically operate only in air, while refraction at the waterline systematically affects both the 3D point cloud and the geometry of partially submerged objects. This study presents a controlled experimental framework for assessing waterline-induced effects in an Underwater LiDAR (ULi) system, using a terrestrial laser scanner (TLS), the Z+F IMAGER 5016A (IMAGER), as an above-water reference. A rigid reference frame (RRF) spanning the waterline was deployed in a swimming pool. First, the RRF was scanned by the IMAGER under in-air conditions to establish its reference geometry. Subsequently, in the waterline configuration, the ULi system measured the complete RRF, while the IMAGER captured only its above-water part. The analysis investigated refraction- and interface-related effects on the 3D point cloud and geometry in the above-water, cross-waterline, and underwater parts of the RRF. For a physically meaningful assessment, the evaluation considered overall geometric deviations and rigid-body-invariant internal quantities, including pairwise distances, which are independent of the overall pose of the RRF. Refractive-index sensitivity was analyzed by perturbing the refractive index and quantifying the resulting changes in the derived geometric quantities. The proposed workflow provides a practical and traceable basis for isolating waterline-related refraction effects, evaluating their impact on 3D point cloud geometry, and assessing refractive-index sensitivity.
Yu Lan, Jiale Wang, Ji Yang et al.· The International Archives o...· 0 citations
Abstract. Monitoring dynamic alluvial rivers is essential for safe inland navigation, yet traditional bathymetric surveys are costly and infrequent. This paper presents an automated method for detecting migrating sandbars by integrating Sentinel-2 satellite imagery with daily water gauge data. Implemented in Google Earth Engine (GEE), the algorithm matches specific water levels with cloud-optimized images to map emerging shoals. Water and sediment were separated using the Sentinel Water Mask (SWM) index, while a 30-meter internal channel buffer mitigated shoreline mixed-pixel errors. The method’s accuracy was validated using 3-meter resolution PlanetScope imagery. Results demonstrated high geometric agreement (mean Intersection over Union = 0.71) and a strong area correlation (R² = 0.97). Notably, the 10-meter Sentinel-2 resolution caused a systematic 26% overestimation of sandbar size. However, for navigation, this overestimation provides a beneficial safety margin that prevents the underestimation of submerged obstacles. By correlating specific gauge levels with sandbar emergence, the extracted 2D contours provide a vital spatial baseline that enables the future estimation of available water columns over specific bottlenecks. Ultimately, this cost-effective procedure allows for the continuous generation of spatial databases, forming a practical foundation for dynamic relative depth mapping within River Information Services (RIS).
M. Smiarowski· The International Archives o...· 0 citations
Accurate bathymetric data are essential for the design and monitoring of coastal structures, but conventional multibeam surveys are costly and often impractical in shallow or confined areas. We evaluate a single-beam echosounder (SBES, ECT400) suspended beneath an unmanned aerial vehicle (UAV) as a rapid method with low logistical requirements for bathymetric monitoring of coastal infrastructure. Fieldwork was performed in an operational dry dock that was alternately drained and filled, enabling direct geometric validation against an ultra-high-resolution photogrammetric DEM (0.55 cm GSD). The co-registered dataset comprises N = 16,137 sonar returns to depths of ≈ 8 m. The UAV-mounted SBES produced a mean depth difference of 0.15 m (SD = 0.58 m) relative to the photogrammetric reference. From these residuals we estimate a 95% Minimum Detectable Change (MDC95) of ≈ 0.5 m when changes are assessed by aggregating repeated co-located passes. These results indicate that the UAV-SBES workflow is suitable as a Tier-1 screening tool for structural-health monitoring, effective for detecting metre- to decimetre-scale changes and triaging sites for targeted high-precision follow-up, but not for micrometre/mm-scale deformation monitoring. The method’s portability and vessel-free operation make it especially useful for frequent inspections in shallow, confined coastal settings.
Bethsaide Souza-Santos, M. Arza-García, J. Ortiz-Sanz et al.· Journal of Civil Structural...· 0 citations