Underwater Ground Research Articles

Evaluation of the Accuracy of Photogrammetric Reconstruction of Bathymetry Using Differential GNSS Synchronized with an Underwater Camera

Abstract. Photogrammetry is a valuable tool for 3D documentation, mapping, and monitoring of underwater environments. However, the ground control surveys necessary for georeferencing and validation of the reconstructed bathymetry are difficult and time consuming to perform underwater, and thus impractical to scale to larger areas. Underwater direct georeferencing, using a differential GNSS receiver synchronized with an underwater camera system, offers an attractive alternative to surveying underwater ground control points in conditions when the seafloor is clearly visible from the surface. In this paper, the design of an underwater direct georeferencing system using mostly commercial off the shelf components is presented. The accuracy of the system is evaluated against geodetic survey based on trilateration and leveling, as well as by RTK (real time kinematic) positioning using a tilt-compensated GNSS receiver mounted on an extended pole to allow measurements of points in up to 7 m in water depth. Tests were conducted in a controlled outdoor pool setting with depths from 1–3 m, as well as in a 10 m × 10 m test plot established on the seafloor in a near-shore environment by Catalina Island, California at depths from 4–10 m. Comparing the geometry of the photogrammetric reconstruction with the geodetic survey yielded sub centimeter consistency, and 1 mm accuracy in length measurement was achieved when compared with calibrated 0.5 m scale bars. Through repeated surveys of the same area, repeatability of georeferencing is demonstrated within expectations for differential GNSS positioning, with horizontal errors at sub centimeter level, and vertical errors of up to 3 cm in the worst cases. These tests demonstrate the benefits of the underwater direct georeferencing approach in shallow waters, which can be scaled up much more easily than measuring underwater ground control points with traditional approaches, making this an ideal option for collecting accurate bathymetry of the seafloor over large coastal areas with clear waters.

Ocean warming events resilience capability in underwater computing platforms

Underwater data centers (UDCs) use the ocean’s cold-water resources for free cooling and have low cooling costs. However, UDC cooling is affected by marine heat waves, and underwater seismic events thereby affecting UDC functioning continuity. Though feasible, the use of reservoirs for UDC cooling is non–scalable due to the high computing overhead, and inability to support continuity for long duration marine heat waves. The presented research proposes a mobile UDC (capable of migration) to address this challenge. The proposed UDC migrates from high underwater ground displacement ocean regions to regions having no or small underwater ground displacement. It supports multiple client underwater applications without requiring clients to develop, deploy, and launch own UDCs. The manner of resource utilization is influenced by the client’s service level agreement. Hence, the proposed UDC provides resilient services to the clients and the requiring applications. Analysis shows that using the mobile UDC instead of the existing reservoir UDC approach enhances the operational duration and power usage effectiveness by 8.9–48.5% and 55.6–70.7% on average, respectively. In addition, the overhead is reduced by an average of 95.8–99.4%.

자유낙하식 콘관입시험 시스템의 표준 운용 절차 제안 및 검증

Recently, research and development on underwater cities have emerged. Hence, research equipment to investigate the characteristics of the seabed is also diversifying. Existing underwater ground survey equipment faces the problem where a large system, high cost, and available ships are limited. Therefore, the FFCPT (Free-Fall Cone Penetration Test) is emerging as a realistic alternative. KIOST in Korea is developing an FFCPT, intending to have a depth of 200m or more and a weight of less than 100㎏. When operating the FFCPT, heavy-load work such as loading on a ship, moving, dropping, and extruding from the seabed is required. It is essential to perform work according to the standard operating procedure (SOP) in consideration of safety. However, there are no studies on SOPs for an FFCPT. Therefore, in this paper, an SOP for an FFCPT was proposed. The result of the total resistance test of the seabed demonstrates the effectiveness of the proposed SOP. Furthermore, we could generalize our work using an FFCPT based on the proposed SOP.

Fundamental study on underwater trafficability for tracked vehicle

In recent years, water disasters have increased in Japan. In water disaster, remote controlled vehicles which work for disaster recovery must run in water environment. Since underwater ground is likely to be soft, the vehicle has a risk of stuck. If a vehicle gets stuck at disaster sites, rescue work is difficult because it is not easily to access to that area. We must make a method for judging whether to run or not. For this purpose, we must quantitatively clarify the relationship between the trafficability and the strength, bearing capacity, etc. of underwater ground. We measured the cone index of underwater ground. From results, we confirmed that fragile layer was formed on the surface layer in underwater ground. We measured drawbar pull of a tracked carrier in test field. As a result, maximum drawbar pull of underwater ground was lower than on the ground. After slip occurs, drawbar pull of underwater ground was smaller than ground significantly.

Structure-from-Motion on shallow reefs and beaches: potential and limitations of consumer-grade drones to reconstruct topography and bathymetry

Reconstructing the topography of shallow underwater environments using Structure-from-Motion—Multi View Stereo (SfM-MVS) techniques applied to aerial imagery from Unmanned Aerial Vehicles (UAVs) is challenging, as it involves nonlinear distortions caused by water refraction. This study presents an experiment with aerial photographs collected with a consumer-grade UAV on the shallow-water reef of Fuvahmulah, the Maldives. Under conditions of rising tide, we surveyed the same portion of the reef in ten successive flights. For each flight, we used SfM-MVS to reconstruct the Digital Elevation Model (DEM) of the reef and used the flight at low tide (where the reef is almost entirely dry) to compare the performance of DEM reconstruction under increasing water levels. Our results show that differences with the reference DEM increase with increasing depth, but are substantially larger if no underwater ground control points are taken into account in the processing. Correcting our imagery with algorithms that account for refraction did not improve the overall accuracy of reconstruction. We conclude that reconstructing shallow-water reefs (less than 1 m depth) with consumer-grade UAVs and SfM-MVS is possible, but its precision is limited and strongly correlated with water depth. In our case, the best results are achieved when ground control points were placed underwater and no refraction correction is used.

Observations of dune interactions from DEMs using through-water Structure from Motion

The role of three-dimensionality (3D) in modulating both flow and sediment transport remains poorly understood. 3D bed elevation measurements are difficult to obtain due to irregular dune shapes and submergence. Using photogrammetric tools for topographic reconstruction has become popular in surface studies, yet water refraction makes through-water image capturing of submerged dunes still challenging. We show that through-water images and Structure from Motion (SfM) tools can produce accurate Digital Elevation Models (DEMs) of a measured dune field, with a high level of detail. It is a low-cost and non-intrusive alternative for submerged bed elevation measurements. We provide a detailed SfM workflow, introduce and discuss the use of camera coordinates and underwater ground control points, and processing steps needed to obtain high accuracy DEMs. Our method results in DEMs with mm resolution in controlled laboratory conditions. New data for 23 dune field DEMs from 6 experiments were obtained and are presented.The dune field DEM time series provide insights on dune interaction processes. In our experiments, merging and defect creation were most common. Merging decreases the number of bedforms, and defect creation is responsible for more bedforms. Dunes continue to interact and jostle after achieving equilibrium. Simple crests are much more frequently observed than irregular, sinuous or double crests. Two-dimensional (2D) crest shapes were observed, although crest shapes were generally of 3D nature. Observed dune migration rates are not steady and vary in time and space. Bedform splitting speeds up dune migration, whilst neighbouring dunes tend to accelerate or decelerate. We identify a cascade of processes and show that 3D DEMs at high frequency are required to resolve observed rapid deformations and interaction of dunes. The identified dune interaction processes are inherent to sediment flux (variability), whereas the temporal component of the underlying sediment transport processes is still not well understood in relation to average transport.

Development of a perforated plate underwater acoustic ground cloak.

One of the commonly investigated transformation acoustic device is the ground cloak, which conceals a scattering object on a reflecting surface. Multiple studies have numerically simulated acoustic ground cloaks, but because of the challenges associated with realizing a homogeneous anisotropic metamaterial, only two acoustic ground cloaks have been built and tested. Perforated plastic plates in air were used to construct two and three dimensional ground cloaks and alternating layers of brass and water were used to construct an extended area ground cloak underwater. With underwater mass density anisotropy previously demonstrated for perforated steel plates, the primary focus of this article is to build and evaluate an underwater ground cloak with perforated steel plates. The cloak was evaluated at a water-air pressure release reflecting surface. The cloak successfully concealed the scattering object over a broad frequency range of 7-12 kHz.

Development of Underwater Drilling Robot Based on Earthworm Locomotion

In this paper, a drilling robot based on earthworm locomotion was developed for seafloor exploration. Seabed mineral resources are found on the bottom of the ocean. The drilling robot developed herein can excavate and obtain samples of seafloor soil. This paper was inspired by the results of the previous study, in which a drilling robot based on earthworm locomotion developed for land successfully demonstrated the ability to create curved boreholes of 1670-mm turning radius and 613-mm depth. By principle, earthworm locomotion is propelled without rubbing the side of the robot against the wall of the borehole. That is, the movement is not affected by earth pressure, and thus it is facilitated deep into the soil region, which makes it is suitable for underground exploration robots. Seafloor explorations, in essence, could be realized by improving the gripping torque of the drilling robot and reducing its drilling torque. To resolve the problem, in this paper, three points were addressed. First, a setae-attached propulsion unit patterned to an earthworm structure was designed to attain an improved gripping torque for a subunit, typically at 30 kPa, by 1.7 times compared to that without setae. Second, the drilling resistance was reduced by the adjustment of the penetration and rotational speeds of the drilling robot based on the drilling properties of underwater ground. Lastly, the shape of the earth auger was considered for the reduction of the drilling torque. Following these solutions, the developed robot succeeded in drilling 430 mm into an underwater soil.

Evaluation of Limit State for Pier According to Scour and Peak Ground Acceleration

Recently, materials and structure analysis techniques used in various structures have been developed and have made remarkable progress. As the design method for reinforced concrete structures is shifting to the limit state design method, it is necessary to conduct the limit state assessment. So far, several researchers have evaluated the safety of many structures covered by the civil engineering field by introducing the limit state assessment. However, there is a lack of research on bridge piers considering the level of scour. Therefore, in this study, T-shaped bridge piers with a height of 11.5 m and a width of 2.8 m installed in underwater ground were selected and the critical condition of bridge pier for 20 seismic waves was evaluated using LS-DYNA. The presence or absence of scouring was also set as a variable and the level of scour is changed from 0 to 5 meter. As a result of the analysis, the main fracture was tensile failure at the maximum ground acceleration of 0.2g to 0.4g, and the maximum ground acceleration after the earthquake was found to be weak as a whole except compression. Finally, as a result of comparing analysis results according to the presence or absence of scour, the limit state reaching ratio showed a similar pattern without significant change.

The Synthesis of Unpaired Underwater Images Using a Multistyle Generative Adversarial Network

Underwater image datasets are crucial in underwater vision research. Because of the strong absorption and scattering effects that occur underwater, some ground truth such as the depth map, which can be easily collected in-air, becomes a great challenge in underwater environments. To solve the issues associated with the lack of underwater ground truth, we propose a trainable end-to-end system of an underwater multistyle generative adversarial network (UMGAN) that takes advantage of a cycle-consistent adversarial network (CycleGAN) and conditional generative adversarial networks. This system can generate multiple realistic underwater images from in-air images using a hybrid adversarial system and an unpaired method. Moreover, our model can translate in-air images to underwater images that retain the main content and structural information of the in-air images under specified turbidities or water styles through a style classifier and a conditional vector. Furthermore, we define the color loss and include the structural similarity index measure loss for the system to preserve the content and structure of original in-air images while transferring the backgrounds of the images from air to water. Using UMGAN, we can take advantage of the in-air ground truth and convert the corresponding in-air images into an underwater dataset with multiple water color styles. Our experiments demonstrate that our synthesized underwater images have a high score on image assessment against CycleGAN, WaterGAN, StarGAN, AdaIN, and other state-of-the-art methods. We also show that our synthesized underwater images with in-air depths can be applied to real underwater image depth map estimation.

E-URoPe: a reconfgurable AUV/ROV for man-robot underwater cooperation

This work describes the new Unmanned Marine Vehicle e-URoPe developed by CNR-ISSIA. This Remotely Operated Vehicle is realized using the most innovative technical capabilities in order to achieve a fexible structure, adequate to withstand external impacts. The peculiar characteristics of the vehicle, on which is based the design concept, are: easiness of construction, facility of re-confguration and fexibility. Furthermore the vehicle could be completely modifed without big eforts in terms of money and time. The vehicle can be equipped with diferent types of sensors in order to make it fexible and adaptable to various applications such as sampling of water or objects, underwater manipulation, cooperation with underwater operators or with other underwater vehicles, mapping of underwater ground and detection of vegetation lying on the seabed.

UNDERWATER GROUND MAPPING FOR FLOOD DISASTER USING ULTRASONIC SENSOR

Search and Rescue (SAR) team used dip stick to measure the water depth and identify the badly eroded area and a guide line will be placed to assist them. However, ground erosion is unpredictable coupled with unknown sizes make the SAR task more difficult thus posing grave danger to SAR team in action. Therefore, this current method is no longer reliable because the flood current will swipe it away and rendered the guide line to be unfeasible over time consuming. A system proposed in this study was developed using ultrasonic sensor array to reconstruct the ground map in flood area. It consists of several sensor arrays to collect the underwater depth information and convert them into mapping data before relaying them to ground station. The results then will help the SAR team to identify the safe path to reach for the flood victims. The factor to focus on is the depth of the flood, the current flow and the medium that the wave will go through. The current flow will be the main threat because the sensor needs to be on the right angle to get the accurate reading. The data then will be transfer to excel to start the mapping for underwater ground. Based on the result from the prototype testing conducted using water tank, sensors can be installed to get wider map view and mapping can be improved by using multi-angle shapes for it to be more accurate in flood disaster.

Methods to Resist Water Current Disturbances for Underwater Walking Robots

AbstractUnderwater robots play an increasingly significant role in helping humans explore or accomplish various tasks in the underwater environment. Underwater walking robots are members of a large group of underwater robots. With the support of multiple legs, underwater walking robots can walk continuously on underwater ground and have good capability to resist water current disturbances. These robots are qualified to perform the tasks that autonomous underwater vehicles and remotely operated vehicles are unable to or cannot efficiently accomplish, particularly exploration, observation, detection, and operation on underwater ground. This paper provides a brief introduction to the development of underwater walking robots and the methods to address water current disturbances acting on underwater walking robots in underwater environments. This study also presents future directions in the methods to resist water current disturbances for underwater walking robots.

Theoretical and Experimental Investigation on Underwater Ground Anchors

AbstractDeepening of harbours has become a priority, necessary to the ongoing operation of the wharves in the face of deeper draft merchant vessels and cruise ships. It is now standard practice in many areas to provide for harbours to be dredged to significant depths below mean sea level, in the order of 12.00 m (39 ft) for existing berths and 15.00 m (49 ft) for new wharf construction. The Ravenna Port Authority initiated a project to deepen the harbour bottom at selected wharves to a depth of 12.00 m (39 ft). In preference to reconstruction of the wharves with longer and heavier sheet piling or other equally disruptive reconstruction, they identified the structural reinforcement of the existing wharves by means of deep underwater tie rods as a possible alternative cost-effective solution.Having defined the design concept, effort was concentrated on developing the required technology. A technique, already in use for the installation of tie rods by means of robotics, was identified as potentially suitable...

제주도 주변해역의 방어어장형성기구에 관한 연구

1. 추.동계에 추자도 주변해역에서 풍어를 보이는 해는 추자도 주변 및 제주해협과 한국남해연안역에 15.0~l8.<TEX>$0^{\circ}C$</TEX>의 고온수가 분포하고 이들 고온수의 등온선 간격이 넓을 때이며, 흉어를 보인 해는 추자도 주변 및 제주해협과 한국남해연안역에 11.0~l4.<TEX>$0^{\circ}C$</TEX>의 저온수가 넓게 분포하여 황해남동부 및 한국남해연안역으로부터 15.0~l8.<TEX>$0^{\circ}C$</TEX>의 고온수가 추자도 주변해역까지 영향을 미치지 못하는 해이다. 2. 마라도 주변해역에서 추.동계 풍어가 나타나는 해는 마라도 주변해역이 황해남동부 및 한국남해로부터 15.0~l9.<TEX>$0^{\circ}C$</TEX>의 고온로 연결되어 있어 황해남동부 및 한국남해로부터 방어가 마라도 주변해역까지 이동하기 알맞은 수온분포를 하고 있을 때이고, 흉어가 나타나는 해는 제주해협에 14.<TEX>$0^{\circ}C$</TEX> 이하의 저온수가 넓게 분포하여 황해남동부 및 한국남해로부터 마라도 주변해역까지 15.0~l9.<TEX>$0^{\circ}C$</TEX>의 고온수가 연결되지 않거나 한국남해로부터 15.0~l9.<TEX>$0^{\circ}C$</TEX>의 고온수가 제주해협과는 연결되지만 마라도 주변해역은 21.0 <TEX>$^{\circ}C$</TEX>이상의 외양수 영향을 받고 있어 한국남해연안역으로부터 마라도 주변해역으로 방어군이 이동하기 어려운 수온분포를 하고 있을 때이다. 3. 추자도 주변해역에 14.<TEX>$0^{\circ}C$</TEX>이하의 저온수가 분포하여 추자도 주변어장은 흉어가 나타나더라도 한국남해연안역으로부터 15.0~l9.<TEX>$0^{\circ}C$</TEX>의 고온수가 제주도의 동.서쪽 연안을 통하여 마라도 주변해역과 연결될 때는 마라도 어장에 풍어가 나타날 수 있다. 그러므로 마라도 주변해역의 추.동계어장은 한국남동부 및 한국남해로부터 월동장 내지는 산란장으로 남하하는 방어군에 의해 형성되고 있다. 4. 추자도 및 마라도 주변해역의 추.동계 방어 어장의 풍흉은 제주도 주변 해역의 수온분포에 의해 크게 좌우되지만 염분분포는 크게 영향을 미치지 않는 것 같다. 5. 마라도 주변해역의 추.동계 방어채낚기어장은 한국연안역으로부터 월동장 내지 산란장으로 남하하는 방어어군이 마라도 주변에 나타나는 연안계수와 외양계수(대마난류) 간에 형성되는 수온.염분전선, 섬주변의 소규모 와, 강한조류 및 지형적 특성(불규칙한 해저지형 및 고립도서)에 의해 이루어지는 왕성한 수평 및 연직 혼합 등과 같은 어장학적 호조건에 의해 마라도 주변에 체류하게 되고, 이들 체류어군은 조류방향에 따라 섬의 조상 측에 농밀군을 형성하는 섬의 조상측 어장이다. We studied the fishing ground of a yellowtail and oceanographic conditions around Chujado and Marado around Jeju Island from autumn to winter. Also we investigate the forming mechanism of fishing ground around Marado, which shows the best catch of yellowtail near Jeju island. The obtained results are summarized as follow ; 1. When the high temperature water about 15.0∼19.0 in depth of 50m distributed around Chujado and Marado, the fishing ground of Yellowtail is shows a good catch. On the contrary, when the low temperature water about 11.0∼14.0 is shows a poor catch. 2. Fishing grounds of yellowtail by handline fishing are formed with a school of Yellowtail migrating southward from the coastal sea of Korea and slaying around Marado to winter and spawn due to following factors. Firstly, a front of temperature and salinity is formed between inshore water and oceanic water around Marado. Secondly, small-size eddies and excellent horizontal and vortical mix which is created by strong tide and geographical features including irregular underwater ground and an isolated island. An abundant school of yellow tails stays in front of the tide where a good fishing ground was made.

Earthquake resistant design of offshore building structures

A proposed earthquake resistant design system for offshore building structures in Japan is introduced. Offshore building structures are defined as the fixed type offshore structures which are constantly utilized for the purpose of habitation, duty, work, operation, gathering, recreation, sightseeing, etc. In the first section, basic principles for the design of offshore building structures are introduced considering safety of human life, maintenance of building functions, and protection of property. In the second section, the seismicity in and around the Japan Islands is determined by utilizing the past earthquake data and recent researches concerning seismicity, and a seismic macrozoning map in Japan is herein revised. In the third section, the earthquake resistant design system based on the basic principles for the design of offshore building structures and the seismicity in Japan is proposed. This system consists of three kinds of earthquake resistant design methods according to the fundamental natural period of the structure: seismic coefficient design, modified seismic coefficient design, and dynamic analysis. The choice of these methods to be used is entrusted to the designer of the structure. In each earthquake resistant design method, two levels of earthquake activity which the structure may be subjected to are considered: strong earthquake design level and severe earthquake design level. The strong earthquake design level requires that the structure be adequately seized for strength and stiffness to maintain the maximum level of earthquake activity which may be expected during the life of the structure. The severe earthquake design level requires that the structure have sufficient ultimate strength or ductility to prevent the collapse of the structure during a maximum credible earthquake. In the final section, the need for seismic instrumentation to acquire ground motion on underwater ground during a strong earthquake is emphasized to establish more efficient earthquake resistant design for offshore building structues as a conclusion.