Jul 2026· The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences· 0 citations· 1 references
Abstract
Abstract. Next to the known photogrammetric or acoustic measurement techniques, nowadays LiDAR is a promising option for high-resolution surveys or monitoring of underwater structures in low turbid and shallow waters. The objective of this investigation is to determine the performance of an underwater laser scanner and an air-borne bathymetric laser scanner for mobile data acquisitions. For this purpose, the underwater LiDAR (ULi) from Fraunhofer IPM is installed on a vessel. To enable the registration and georeferencing of the scan data, ULi is added by an Inertial Navigation System (INS) and two GNSS antennas. On the other hand, the air-borne bathymetric laser scanner (ABS) is integrated into an unmanned aerial system (UAS). Both systems are used to survey in the same measurement area to acquire comparable data sets. With the selected measurement settings, both systems can penetrate through water for more than 10 m and are able to resolve small underwater structures. Caused by shorter measurement ranges, ULi offers a point density which is approximately four times higher than the ABS and is able to resolve vertical underwater structures. The advantage of the UAS mounted ABS is that it can survey in shallow areas which cannot be accessed by vessels.
Abstract. Mapping at the air–water interface in shallow coastal environments remains challenging due to the need to integrate heterogeneous datasets acquired under different geometric and operational conditions. This study presents a modular uncrewed surface vehicle (USV)-based system for simultaneous above- and underwater photogrammetric surveying supported by differential GNSS positioning. The system integrates a rigid multi-camera configuration, GNSS time synchronization, and a direct georeferencing workflow based on trajectory interpolation and lever-arm calibration. Experimental results from a rocky coastal site in Sardinia (Italy) show that underwater photogrammetry can achieve centimetric absolute accuracy (2–4 cm horizontally and ~8 cm vertically) without underwater ground control points. The USV enables controlled and repeatable acquisition in very shallow environments, while UAV photogrammetry complements the reconstruction of the emerged area. Limitations related to image quality and refraction effects are discussed. The system represents a flexible and scalable solution for integrated coastal mapping and monitoring.
Sergey Khokhlov, F. Menna, E. Nocerino· The International Archives o...· 0 citations
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
Commercial underwater noise recorders are expensive and often vulnerable to loss or entanglement in fishing nets, while developing affordable alternatives is challenging and requires expertise in electronics and low-level programming. Consumer-grade microcomputer platforms offer a cost-effective and efficient solution for monitoring underwater noise, particularly in shallow coastal areas. This paper investigates a method for developing an autonomous underwater acoustic recorder based on earlier work. The developed system able to store acoustic data over mid-term deployments and is suitable for applications such as environmental noise assessment, aquatic animal monitoring, and recording impulsive or vessel-generated noise. The performance of the developed device was validated in air using a purpose-built acoustic coupler and sine wave signals, following a comparative hydrophone system calibration procedure and tested during the field measurements in the Klaipėda Harbour area, Lithuania. • Development of a low-cost autonomous underwater sound recording system. • Validation of the system using a comparative hydrophone calibration procedure. • Experimental measurements of ship noise using the developed system.
D. Bagočius, Aleksas Narščius, Gintaras Kučinskas et al.· MethodsX· 0 citations
Underwater laser imaging is widely used for deep-sea exploration, autonomous underwater navigation, and inspection of marine infrastructure, where high-precision observation under optically challenging conditions is required. These imaging systems are inherently limited by absorption attenuation, volume scattering, and backscattered noise, leading to reduced visibility, low contrast, and loss of structural details. In this study, we propose a Polarization-Constrained Multi-Scale Defogging and Restoration (PCMS-DR) algorithm designed for turbid and heterogeneous aquatic environments, specifically targeting submerged engineered structures, pipelines, and other objects of interest. The method integrates polarization feature constraints with multi-scale decomposition, enabling robust separation of backscattered light and target-reflected signals while preserving high-frequency structural information. To quantitatively evaluate the proposed framework, two complementary validation strategies are adopted. First, polarization-resolved Monte Carlo photon propagation simulations are conducted to generate physically consistent synthetic underwater laser images for controlled analysis under different scattering conditions. Second, real-world validation is performed using 12 self-acquired coastal underwater laser imaging scenes collected under representative aquatic environments. The simulation and experimental datasets are analyzed separately to ensure that the quantitative evaluation accurately reflects both physical restoration capability and practical applicability. Quantitative results from the Monte Carlo simulation experiments demonstrate that the proposed PCMS-DR method achieves a peak PSNR of 26.52 dB and an SSIM of 0.836 under representative low-turbidity conditions, outperforming polarization-only and multi-scale-only baselines. In addition, evaluation on the self-acquired real underwater laser imaging dataset containing 12 coastal scenes indicates an average backscatter suppression ratio of 22.3% and a local contrast enhancement ratio of 1.62. These results confirm that the proposed method improves image visibility and structural preservation across both controlled simulations and practical imaging scenarios. Furthermore, evaluation on 12 real coastal underwater laser imaging scenes demonstrates an average backscatter suppression ratio of 22.3% and a local contrast enhancement ratio of 1.62, indicating improved visibility, contrast, and structural fidelity. The principal novelty of the proposed framework lies in the unified integration of polarization-constrained backscatter modeling, multi-scale transmission estimation, and physically guided detail restoration within a single optimization framework. The experimental results demonstrate that the proposed PCMS-DR framework provides physically interpretable and effective restoration performance under the tested turbidity range for underwater laser imaging applications.
Jun Yan, Xun Yu· Journal of Marine Science an...· 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. 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.
Lucas Dammert, Jan Rhomberg-Kauert, P. Amon et al.· The International Archives o...· 0 citations
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