Hekmatollah Mohammad Khanlu; Mahdi Modiri; Elahe Khesali; Hamid Enayati
Abstract
Introduction
Hydrography is a science used for regular measurement of parameters such as depth of water, geophysical geology, tide, water flow, waves and other physical properties of seawater. It is also used for the production of maritime maps. Hydrography contributes significantly to the internal ...
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Introduction
Hydrography is a science used for regular measurement of parameters such as depth of water, geophysical geology, tide, water flow, waves and other physical properties of seawater. It is also used for the production of maritime maps. Hydrography contributes significantly to the internal infrastructure of coastal countries. Providing proper hydrographic services ensures safe and efficient sailing. Thus, development of hydrographic services on the national level can improve safety of mariners, and protect people’s lives and belongings on the sea, while providing some facilities for the protection of marine environment. The advancement of space technologies in recent years has increased the speed of spatial information production and facilitated sea monitoring.
Materials and Methods
Different methods are used for bathymetry. Lyzanga et al (1978) used a linear combination of the logarithm of corrected radiance ratio. This method is based on the simplification of Beer's physical model in which a linear equation of five unknowns is obtained for two bands. In 2006, Lyzanga et al. presented an improved version of their model. Using Tow-Bands Reflection Ratio, Stampf et al (2003) not only reduced the number of unknown variables in Lyzenga method, but also decreased the sensitivity of depth determination to different substrates. In this method, the difference between absorption properties of green and blue bands is used. TCarta is a global supplier of geospatial products. The company generated Satellite Derived Bathymetry (SDB) dataset by accurately extracting water depth from multispectral imageries received from the European Space Agency’s Sentinel-2 Satellite. The resulting bathymetric data had a point spacing of 10 meters, while measuring up to a depth of 15 meters. Data covered a 30-square kilometer area around Preparis Island on the Bay of Bengal.
The present article used images received from Sentinel-2 in 7 different periods for depth determination, and 1: 25,000 ADMIRALTY Nautical Charts for accuracy evaluation. Following the assessment of water transparency in received images, the 12/15/2018 image was used for depth determination. Case study area contains around 130 km along the Port of Salalah, Oman.
Results and Discussion
In order to implement the model, it is necessary to separate land from water in images using NDVI, NDWI, MNDWI and AWEI indices. The NDVI index has been used in this project. NDVI is primarily used to estimate vegetation cover, but since this index exhibits a negative value in areas covered with water, this property is used to provide a mask for separating land from water. In this step, 68 control points and 68 check points were selected from the existing ADMIRALTY map. The DN values of the corresponding pixels of the selected points were extracted from four 10-meter bands of Sentinel-2 images. The control and checkpoints and the DN value of their corresponding pixels were extracted in 4 separate files, then these 4 files were logged into the Bathymetry software and the parameters of LMR and Stumpf methods were calculated. The root mean square error (RMSE) and correlation coefficient (CC) were used to assess geometric accuracy. In order to extract necessary parameters for each model, RMSE= 2.15 m and CC= 92.5% were calculated at depth distances of 0 to 20m. Results indicates higher accuracy and stronger correlation of LMR findings. Therefore, this method was used for depth determination between 0 to 20 meters. The 5 parameters extracted from the Bathymetry software and the corresponding pixel values of the four bands with 10-meter resolution extracted from the Sentinel-2 image (received from the on 12-15-2018) were used as input. Linear Regression Model was applied to transform 4 bands of Sentinel-2 image into depth. The output of the model (depth) was presented as the Substrate DEM of the coasts of Port of Salaleh, Oman.
Conclusion
Hence, it can be concluded that Remote Sensing technologies can be used for depth determination and sea monitoring at critical times (during wars or other periods of insecurity) for an acceptable time period. It also provides an appropriate context for bathymetry of inaccessible coastlines and monitoring of strategic widespread water zones. In this way, the depth of sea bed in shallow areas is extracted using spectral analysis of satellite data and different models.
Amir Mahdi Emamizadeh Mahabadi; Kamran Lari; Mojtaba Zoljoodi
Abstract
Extended Abstract Sedimentation in ports’ access channels is a major problem for the port authorities as well as the vessels navigating in these channels. This phenomenon creates dangers for the ships in this vital part of the port in addition to imposing heavy costs on the port. In this research, ...
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Extended Abstract Sedimentation in ports’ access channels is a major problem for the port authorities as well as the vessels navigating in these channels. This phenomenon creates dangers for the ships in this vital part of the port in addition to imposing heavy costs on the port. In this research, we evaluated and estimated the sedimentation rate and volume in Imam Khomeini port’s access channel based on field information as the research goal. In this research method, analyses on the geographic status such as bed level, analysis of wave time series and tide (as current) were carried out in the region by Mike 21 software, and appropriate modeling was presented. To investigate the rate and volume of sedimentation, the methods of hydrography, Bijker’s theory and modeling by Mike 21 were used. In the present study, hydrodynamic model of current and sediment transport will be carried out using valid engineering methods. At the same time, all information and library data and the results of existing field data are collected and analyzed, and the results obtained from different methods (Hydrography, Bijker and Mike 21) are calibrated. In line with the objectives of the study, the following cases can be summarized as: - Collecting required data and statistics such as wind, wave, current, sediment characteristics of the region or grading, and sounding data. - Investigating the variety of dredging methods and equipment available in the world. - Examining different types of discharge methods, and diverse applications of the extracted sediment. - Computations and modeling. - Summing up and conclusion and analyzing the results. The hydrographic boat moves on specific paths according to a predetermined schedule in order to estimate the depth or carry out the sounding. The boat is equipped with a dual or multi-frequency GPS device and a sonar device. The boat receives its horizontal position from the GPS. The sonar sends an audio wave to the bed during the movement, and gives the depth for each point by calculating the wave’s round-trip time and the sound velocity profile, and on the other hand, the GPS provides the horizontal position of that point. Today, various software are capable of simultaneous recording of this information, which is used in hydrographic vessel. Based on the obtained results and investigating the hydrographic maps, the actual amount of sedimentation in the channel (0/000078m^3/s/m) was obtained. Given that, the criterion hydrographic method was taken into consideration for the work and calculations in other ways, the error percentage of the results obtained from Bijker’s and modeling of Mike’s calculations were 12% and 20% respectively. Accordingly, the dimensionless coefficients of á=0.88 and =1/2 were obtained for Bijker’s theory and the results of the calculations by Mike21 respectively, which indicates good accuracy. Based on the results, the optimal method of dredging and the morphological changes of the region can be achieved based on the obtained models. Considering the sediment granularity diameter D_50=6ìm, it can be concluded that the most suitable method for dredging with regard to available facilities in the port is the use of self-propelled hopper suction dredger. However, if the dredging unit is equipped with new equipment such as bed leveler device, more optimal methods can be obtained. By this method, the total volume of sediment was 244466.280 cubic meters for an area of 57213810.4 square meters. Of course, this was the volume of solid materials, and according to the experts of the Ports Organization, this amount is 20% of the total volume of the total sediment (solids and water). It can be concluded by a simple calculation that the sedimentation rate in a one year period is about 13.7 cm per square meter per year, which shows a good approximation compared with the field measurements conducted by the Ports and Maritime Organization with a value of 13.5 cm per year. Bijker (1971) presented a method for calculating sediment transport in a combined state of wave and current. This method was expanded to calculate the sediment transport of the coastline. Bijker modified the Fryjling-Kalinske formula for the bed sedimentation along with the Einstein method to evaluate sediment transport applied in coastal environment. For this reason, the Bijker formula is very popular among the European engineers. Among the world’s leading mathematical models in analyzing the phenomena governing the sea environment, Mike21’s mathematical model is one of the most well-known ones. This advanced software has been founded, completed and developed by the Hydraulic Institute of Denmark over time and in collaboration with the Water Quality Institute of this country. This software is a comprehensive system for modeling two-dimensional free flows in which fluid flow layering cannot be ignored.
Mohsen Hassanzade Shahraji; Ali Mohammadzadeh; Kurosh Khoshelham
Volume 20, Issue 80 , February 2012, , Pages 34-39
Abstract
In recent years, a new sensor called Lidar Continuous Wave has been introduced into the commercial laser scanners family. The main advantage of this new type of sensors is the complete recording of the return pulse after the collision with various ground features along the path of the laser pulse to ...
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In recent years, a new sensor called Lidar Continuous Wave has been introduced into the commercial laser scanners family. The main advantage of this new type of sensors is the complete recording of the return pulse after the collision with various ground features along the path of the laser pulse to the surface of the ground. With full wave recording, the output of the cloud of points has a higher density and more reliability, along with new parameters, including pulse widths and pulse amplitudes for each point. These new parameters help us analyze and investigate outcomes of the three-dimensional cloud of points of these types of sensors ever more correct and comprehensive . Lidar's output can be applied in various fields, including updating 3D databases, extracting ground features, providing a 3D model of buildings, providing forest models, urban management and planning, traffic management, air pollution control, tourism industry, crisis management, and many other applications. In this article, we first discuss some points about the Lidar Continuous Wave sensor, the signal processing carried out on it so far, and how to extract the three-dimensional points from it. Examining different types of these sensors and a brief history of their evolutionary process forms the next section. In the end, various applications of this data in forest, urban and hydrographic fields are discussed.
