1. Project Background

Hydro-Tech participated in the sea-sweeping survey task of a harbor basin channel and water intake water area project. Target to maintain and measure the harbor basin channel and water intake of the wharf, obtain the water depth data information and current underwater topography of the scanning area. Check the silting situation in the survey area and to obtain shallow point data in the area to guide the navigation and berthing of ships.

1.1. Scanning Area Introduction

This scan task has two survey areas, one is the harbor basin and channel waters, the other is the water intake area. Total section area around 2.75 square kilometers. Survey operations adopts multi-beam bathymetry technology. The following figure is a schematic diagram of the scanning area:

Figure 1.1  Range planning of survey area

   2.Equipment

MS400 is the latest high-frequency shallow water multi-beam echosounder developed by Hydro-Tech. It's mainly used in shallow water fields such as inland rivers, ports, waterways, and coastal zones. The system is portable and also has high-resolution, high-performance and other features, which can effectively reduce operator's on-site workload.

MS400 has built-in attitude indicator, which integrates acoustic matrix, attitude measurement and GPS. The system can free the user from cumbersome process of installation and calibration during measurement, it's also compatible with external high-precision attitude indicators.

Figure 2.2 MS400 multibeam echosounder

3、Surveying Implementation

This measurement adopts combined method that configure MS400 multi-beam sounding system with external attitude instrument and external GPS.

The figure below is a schematic diagram of the system composition of the MS400 multi-beam sounding system.

Figure 3.1 Construction - MS400 multibeam sounding system

3.1 Field Survey Implementation

3.1.1 Installation

Based on the characteristics of the surveying vessel, the installation method of MS400 adopts multi-beam mounting bracket + adapter flange, and the measuring course introduces suspension installation method of the sounding system.

The picture below shows the on-site multi-beam mounting bracket and adapter flange:

Figure 3.2 Mounting bracket+adpter flange

Figure 3.3 Surveying vessel

Figure 3.4 MS400 and mounting bracket

3.1.2. Measuring line layout

The main principle of measuring line layout is to meet the multi-beam full coverage measurement of the survey area, and the strip overlap between adjacent survey lines should not less than 20%. The layout of the multi-beam sea-sweep survey line for this project is as follows:

The main survey lines for harbor basins, turn-around areas and some channels are arranged parallel to the front line of the wharf, and the distance between the survey line is flexibly arranged at four times the water depth to ensure full coverage of multi-beam scanning. A total of 28 main survey lines are arranged in this area; The main measuring line is about 27km long. The main survey line of the channel is laid out parallel to the center line of the channel, and a total of 11 main survey lines are laid out with a length of about 38km. A total of 6 inspection lines are arranged in the direction perpendicular to the main survey line, with a length of about 0.75km. The layout of the survey lines is shown in the figure below:

Figure 3.7  Survey line mapping layout

1.1.1. Acquisition of sound velocity profile data

Due to the complex situation on site, in addition to the originally designed SVP data collection site for sound velocity profile data collection, a SVP data collection point was temporarily added at the farthest end of the channel. There are three SVP data collection points at both ends and the middle turn. Collection points, as shown in the figure below is the location distribution of SVP collection points and the photo of the sound velocity profile data collected by the engineer on site:

Figure 3.8 SVP collection point layout

Figure 3.9 Engineer is collecting sound velocity profile data

1.1.2. Multibeam Data Acquisition 

After the MS400 multi-beam sounding system is installed, display and control software and navigation acquisition software are used on site for display and control sonar control and data acquisition, as shown in the following figure for on-site data acquisition and navigation:

Figure 3.10 Display control software

Figure 3.11 Navigation software interface

4. Data Post0-Processing

The multibeam post-processing mainly uses hypack software to process the data. The main procedure includes data conversion, data loading, multibeam installation deviation calibration, strip editing, section editing, and result output.

The main process is briefly described below.

4.1. Data loading

After Hypack loads the data of this survey, we can conduct a preliminary screening based on the actual effective survey line, so as to make the office work more efficient. The following figure shows the actual effective survey area survey line data track line:

Figure 4.1 Survey line & track line

4.2. Multibeam Installation Deviation Calibration

After the data is loaded, firstly perform multi-beam installation and calibration on the data. The following figure shows the interface for multi-beam calibration using hypack software.

Figure 4.2 hyapck calibration interface

4.3. Strip Edit

Use hypack software to remove noise from the strip data.

Figure 4.3 hypack strip edit interface

4.4. Section Edit

After using the hypack software to edit the strips of the data, the noise data was deleted through the method of section noise deletion in the three-level editing stage.

Figure 4.4 hyapck section edit interface

5. Data Results

After the above data processing work, we can output the water depth data of the survey area, at the same time provide data basis for the follow-up work.

5.1. Depth Figure

The direct measurement results of multi-beam bathymetry data——water depth data, the following figure shows the renderings of the scanning water depth data results according to different depths in different colors:

Figure 5.1 Overall water depth effect map

Figure 5.2 Partial water depth spread point map

Figure 5.3 Partial water depth spread point map

5.2. 3D point cloud

After obtaining the water depth data, we use the point cloud tool to directly display the bottom of the survey area in the form of a point cloud. The following figure shows the 3D point cloud of the bottom:

Figure 5.4 Overall 3D point cloud map - top view

Figure 5.5 Overall 3D point cloud map - squint

Figure 5.6 Partial 3D point cloud map

Figure 5.7 Partial 3D point cloud map

Figure 5.8 Partial 3D point cloud map

6. Conclusion

Multi-beams are used for full-coverage measurement in the channel waters of the harbor basin, and the data density and measurement accuracy meet the technical requirements of sea-sweeping measurement.