Project Background

As worldwide marine resources protection becomes more and more important, the understanding of the oceans is gradually increasing. Efforts in marine environmental & resources studies and the acquisition of basic marine data are all in full swing. In terms of acquiring bathymetric and seabed terrain data, multibeam echo sounders play a vital role. Multibeam echo sounders primarily utilize sound wave transmitting characters in water, combined with high-precision sound velocity, attitude, and positioning, to obtain underwater contour profile, thereby constructing a real 3D seabed topography. This provides fundamental data for developing, utilizing, protecting, and managing the oceans.

Multibeam Introduction

Conventional underwater 3D topographic surveys generally use multibeam echo sounder with a single transducer. During survey measurement, the quality of the edge beams deteriorates rapidly, which limits the effective coverage to only 4-6 times of the depth. The main reason is the significantly reduced effective array aperture of the edge beams. For large-scale underwater topographic mapping, this results in relatively low efficiency.

To enable rapid and extensive surveying, we have adopted V-shaped dual-transducer measurement technology and developed the first domestically dual-transducer multibeam echo sounding system — MS8200-IDH. This system is based on Hydro-Tech MS8200 multibeam echo sounder, combined with high-precision sound velocity profiler and sensor, POS inertial navigation system and other equipment. It achieves approximately 10 times of the coverage swath, significantly enhancing the efficiency of marine surveying.

System Composition

· 2 sets of MS8200 multibeam echo sounder
· 1 set of POS inertial navigation system
· 1 set of SVS1500 sound velocity sensor
· 1 set of SVP1500 sound velocity profiler
· HydroQuest 2024 display & control software and HydroNavi survey & data acquisition software
· Multibeam post processing software
· UPS Power supply
· 1 set of tide gauge
· 1 set of robust mounting pole

Technology Breakthroughs

1.Utilize coherent depth sounding technology to address the difficulty of detecting outer echoes when the transducer is tilted.

2.Optimize the algorithm to eliminate secondary echoes, resolve the issue of remote surface interference in shallow water during dual-transducer sounding detection.

3.Enhance the energy density of edge beams, thus overcome the problems that edge echo signals is poor and achieve ultra-wide coverage in deep water.

4.Optimize the algorithms of terrain tracking and automatic working parameter for tilted transducer modes.

Questions about MS8200-IDH

1. How does MS8200-IDH reach 10 times the wide sweep width?

For the shallow water environment, the key factors that determine the coverage width are mainly the influence of edge beam width and reverse grazing angle. Due to the V-shaped array of dual heads, comparing with the single head’s installation mode directly toward seabed, the angular resolution of the edge beam angle is obtained. This is a huge improvement, shrinking by 4 times at 80 degrees, effectively reducing the edge beam footprint. According to actual survey, the effective swath reaches about 100 meters when the water depth is 10m.、

Example 1:

In the survey area, the water depth is 8.31 meters, the single-side scanning width is 57 meters, the coverage width of a single survey line of the dual heads is 114 meters, and the scanning width can reach 13.71 times of depth;

Example 2:

In the survey area, the depth is 12.43 meters, the single-side scanning width is 71.47 meters, and the swath of a single survey line of the dual heads is 142.94 meters, which can reach 11.5 times of depth;

2. How about the data quality?

Taking the above [Example 2], we conduct and compare the edge data analysis, data stitching analysis, and comparative analysis of main and test line accuracy.

Edge Data Analysis:

1. • There are some bright noises at the edgebeams of the dual heads, which can be quickly and automatically removed through the software filtering function, without the need to manually remove outliers;
   • After statistics, the number of highlighted noise points accounts for 2.67% of the total measurement points, and the proportion of consistent points is 97.33%, which complies with the "IHO Hydrographic Survey Specification S-44" and the survey technical requirements of the multibeam bathymetry system.

Data Stitching Analysis:

The data of the dual heads can be completely stitched together, and so does the overlapping part can match together too; The cross-sectional of different areas all can be spliced together;

Comparative analysis of main and test line accuracy:

• • The data used for main inspection comparison is from left angle 78°, right angle 79°, and coverage width 134.2 meters, which is 10.8 times of the depth;
  • Create TIN models for two sets of multibeam data results, and perform difference processing on the TIN models. Blue is the main survey line and red is the inspection line area. The renderings and range of the two sets of multi-beam data results are as follows:

After statistics, the proportion of error values less than or equal to ±0.2 meters accounted for 98.7%, which is better than the regulation requirements.

 3. How much better is the MS8200-IDH dual head compared to the single head?

Through the analysis of the effective swath of multi-beams, it is shown that the survey efficiency of dual head has been significantly improved comparing to a single head. However, how much can it actually be improved and how much human and material costs can be saved, these two questions can be answered through a set of test data: Single/Dual head test comparison in 10m deep water.

• • Four survey lines of continuous dual-head multibeam data in the depth of about 10 meters water, which aresurveyed from 11:31 to 14:46, taking 3 hours and 15 minutes, and the average speed was 5.5 knots (10.29km/h)

    

    Survey Line: 26.139km

    

    Survey Area: 2.47km²

  • After the dual heads survey is completed, a single head surveyed in the same water area. In order to ensure the accuracy of the test results, the vessel, test personnel, auxiliary equipment, ship speed, etc. are all same as the dual head. After surveying and mapping, the swath of a single survey line with a single head is about 40m, mapped 2.47km² sea area, the survey time is 6.67h, and the total length of the survey line is 65.12km.
  • By comparing the measurement data of single/dual heads in the same water area, while ensuring that other factors remain unchanged, the survey time of the dual heads is shortened by 52.77%, and the total length of the survey line is reduced by 59.86%.

【Example】

For a oceanology surveying and mapping project, the water depth is about 20 meters, the planned survey area is 600km², and the client estimates that the operation time will be 30 days. After our engineer communicated to the client and checked the environment, we reached a consensus and decided to use MS8200- IDH dual heads multibeam echo sounder to carry out the survey. In the end, it took 15.5 days to complete the planned survey mission. The total length of the survey line was 3700km, saving nearly 50% of the time for users to complete the project, truly get twice the result with half the effort. MS8200-IDH received favorable comments from our clients.

Through the analysis of the swath, data and actual survey efficiency of the dual heads, the MS8200-IDH has nearly doubled the efficiency in large-area ocean surveying and mapping, saving more than 50% of operating time and investment costs.