Jul 2026· Journal of Civil Structural Health Monitoring· Vol 16· 0 citations· 31 references
Abstract
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.
Background: Coastal port infrastructure operates in dynamic tidal environments where seabed change threatens structural safety, yet high-resolution, standard-benchmarked bathymetric validation of damaged and replacement piles is scarce for West-African ports.
Objective: To characterise seabed conditions and validate proposed replacement piles at Bullnose Jetty, Apapa Port Complex, Lagos Lagoon, Nigeria, ahead of piling and repair.
Methods: A single-beam echo-sounder with RTK-GNSS and 10-minute tidal reduction produced a 0.1-m grid, interpolated by kriging (Surfer 16). The survey polygon was stratified into four hydrographic sub-zones (n = 108 nodes); six parameters were analysed by one-way ANOVA with Tukey HSD, Pearson correlation, multiple regression and PCA, and benchmarked against IHO S-44 (Ed. 6.0.0).
Results: Corrected depths ranged 10.1–13.2 m and differed significantly among zones (11.66±0.86 m; F(3,104)=131.0, p<0.001, η²=0.79), deepening from the quay apron (10.65±0.35 m) to the central channel (12.76±0.42 m). Achieved total vertical uncertainty (0.23–0.27 m, k=2) met IHO Order 1a everywhere and Special Order in sheltered zones, and was governed by roughness and depth (R²=0.82). PCA captured 86.3% of variance in two components. No obstructions occurred at piles A-38/39/40; the broken pile P39A was mapped on the seabed.
Conclusion: The reproducible, IHO-benchmarked protocol confirms safe pile placement and supports routine hydrographic monitoring of Lagos-area port infrastructure.
A. Alademomi, J. Odumosu, Stephen Olushola Oladosu· Sriwijaya Journal of Environ...· 0 citations
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. 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
Bridge infrastructure in sub-Saharan Africa is often monitored with limited resources, leaving many ageing structures without a reliable geometric baseline for tracking deterioration. This paper reports on a UAV photogrammetric inspection campaign conducted on the Old Cotonou Bridge, a two-lane reinforced concrete structure crossing the coastal lagoon of Cotonou (Benin), with the aim of establishing a quantitative geometric reference for deck deformation monitoring. A flight of 573 images was captured at 56.1 m altitude using a DJI Mavic 2 Pro equipped with a Hasselblad L1D-20c 20 Mpx sensor (GSD: 1.28 cm/px), and the dataset was processed with Agisoft Metashape Professional 2.3.1 following a Structure-from-Motion and Multi-View Stereo workflow. Processing yielded a dense point cloud of 26.8 million points at 383 pts/m
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, a DEM at 5.11 cm/px, and a georeferenced orthomosaic in WGS 84 / UTM zone 31N; six thematic classes were identified by automatic classification, followed by manual verification of the Road and Building classes. Deck deformation was then quantified through 2D polynomial regression of the deck surface, revealing seven statistically significant depression zones (D1–D7) with amplitudes ranging from −17.3 cm to −79.4 cm relative to the reference surface, over areas of 2 to 30 m
2
. The vertical accuracy achieved (RMSE Z = 0.44 cm) confirms that UAV photogrammetry can reliably serve as a quantitative tool for structural deformation detection on bridge decks, despite the use of only three Ground Control Points. The geometric reference dataset (T
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) produced here places at the disposal of asset managers a georeferenced database that is immediately usable for prioritising maintenance interventions on this and comparable structures.
Kora Yarou, V. Doko, Boris Ganmavo et al.· Journal of Civil, Constructi...· 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
Abandoned, lost, or otherwise discarded fishing gear (ALDFG) is a persistent form of marine pollution requiring survey approaches capable of resolving individual items across large spatial extents. While uncrewed aerial vehicles (UAVs) can capture imagery at resolutions sufficient to resolve individual debris items, their use remains largely constrained to visual line-of-sight (VLOS) operations, limiting large-scale coastal monitoring. This case study develops and field-tests an operational framework for low-altitude beyond visual line-of-sight (BVLOS) UAV surveys, in which DEM-based communication viewshed modelling incorporating first Fresnel zone clearance is used to plan BVLOS missions. A lightweight fixed-wing UAV flown at 60 m AGL completed 20 missions across 210 km of remote northern Australian coastline. Communication viewshed modelling reliably guided mission planning with 90.5% of waypoints placed within predicted high-clearance zones maintaining moderate-to-strong command-and-control (C2) link quality in flight. Manual screening confirmed that the resulting imagery was of sufficient quality, with 291 derelict fishing nets detected. In a simulated VLOS operational scenario, 76.3% of these detections fell beyond VLOS range, and equivalent coverage would require an estimated 8.8-fold increase in mission count. These findings demonstrate that fixed-wing UAVs operating under low-altitude BVLOS conditions can support large-scale image acquisition in remote coastal areas, particularly when enabled by communication-aware mission planning.
Aliesha Hvala, Anindilyakwa Rangers, Hamish A. Campbell· Drones· 0 citations