High-precision and high-resolution acquisition of global seabed topography
Acquisition of High-precision and High-resolution Global Seabed Topography
- Chinese keyword
- Global seabed topography, global ocean sound velocity field, multi-mode topography acquisition, multi-source information fusion
- English keyword
- Global Seabed Topography, Global Marine Sound Velocity，Multi-model Seabed topography Acquisition, Fusion of Multi-source Topography Information
Background of the problem: (Briefly introduce the background of the problem in the current academic research and scientific and technological development)
At present, seabed topography is mainly obtained by means of measurement and measurement information fusion.
Measurement: (1) At present, high-precision and high-resolution seabed topography is mainly obtained by densely wired single-beam or multi-beam bathymetry systems. The former is time-consuming and laborious, while the latter often adopts isometric measurement mode. The interval of measurement points increases with the increase of beam incidence angle and depth, especially the edge beam. The bathymetry results in deep water area are difficult to accurately reflect seabed topography. Reducing the sweep width and ship speed can improve the resolution of bathymetry results, but the efficiency will be significantly reduced. (2) High-resolution seabed geomorphological images are mainly obtained by side scan sonar system. The resolution of more beam sounding results is improved by 10 ~ 100 times, which can present fine seabed texture. However, due to the influence of measurement mechanism and environment, the images have defects such as inaccurate positioning, distortion and inability to reflect the elevation of ground objects. (3) Coherent multi-beam takes into account the advantages of beam-controlled multi-beam and side-scan sonar, and can simultaneously obtain high-precision and high-resolution topographic information. However, with the increase of water depth, the effective coverage width becomes narrower, and the credibility of edge beam bathymetry results decreases. In addition, due to the significant influence of ship posture and complex seabed, data processing is complicated and difficult. (4) AUV/ROV integrated measurement system can approach the seabed to obtain high-resolution topographic information, but due to the influence of carrier positioning accuracy and speed, the accuracy of the results is not high and large-area measurement is difficult.
In order to solve the shortages of precision, resolution and efficiency in obtaining seabed topography by existing survey methods, According to the complementarity of multi-beam and side-scan sonar measurement information, Mainly includes: Depending on the target image shadow, Combining with the side scan sonar imaging mechanism, Although restoring the whole target by scanning images around the target in all directions and fusing with bathymetric data enrich the bathymetric results, there are still some problems, such as time-consuming and laborious, only recovering significant targets with low accuracy, difficult to accurately match and fuse with bathymetric data due to inaccurate image position, and little contribution to bathymetric resolution. (2) SFS (Shape From Shading) algorithm is based on illumination theory and can realize high-resolution seabed terrain restoration in large areas according to the change of image light and shade, but requires external constraints; Only the relative shape of terrain can be obtained, lacking absolute datum and scale information. The problems of inaccurate position and distortion of side scan sonar images are not considered, and cannot be accurately matched and fused with bathymetry results. (3) by match that isobath of the target terrain and the contour of the corresponding image, the accurate position information of the former is used to solve the problem of inaccurate position of the latter, so as to realize the acquisition of high-precision geomorphological images, but the matching success rate is low due to the influence of sounding resolution and target size; Only large target images can be corrected, and other regional problems cannot be solved. At present, multi-beam systems can basically provide each beam echo timing and can form Snippet images with 10 times the sounding resolution. However, research on image generation and processing, matching and fusion with side scan sonar images still needs to be further studied.
Compared with the measurement method, the information fusion method has more advantages. Although there are many problems in the current research, it provides a new way for the rapid acquisition of high-precision and high-resolution seabed topography information. The theoretical and methodological research in this field plays an important role in further exploring the application potential of existing equipment measurement information, enriching the theories and methods of obtaining high-quality seabed topography information, and developing new instruments and equipment and data processing software systems.
Key Breakthrough Point: (Briefly introduce the latest progress of this issue and the key difficulties and challenges in the future)
The current progress is mainly manifested in the following aspects:
(1) A complete set of theories and methods have been initially formed in the aspect of high-precision multi-beam bathymetry in the whole sea depth. The prototype software system has been formed, which breaks the current situation that the multi-beam bathymetry data processing software is monopolized by foreign countries. However, the completeness and performance of the software need to be further improved, especially in the deep sea bathymetry data processing.
(2) In the aspect of wide-scan side-scan sonar image processing, a complete set of theories and methods have been formed, and a prototype software system has been formed, which breaks the current situation that side-scan sonar data processing software is monopolized by foreign software. The software performance needs to be further improved.
(3) The theory and method of 3-D seabed topography inversion based on 2-D side scan sonar images have been preliminarily formed, which improves the resolution of bathymetry by nearly 100 times and the accuracy is close to that of multi-beam bathymetry, but it is only suitable for single-strip topography inversion, and there are further improvements in the theory and method of large-area topography inversion. In addition, the external water depth is still needed as a constraint to provide a reference frame for it in order to obtain absolute seabed topographic changes.
(4) The research on orthogonal modeling of sound velocity field in large area has been carried out, and the sound velocity field in small area has been obtained, which improves the accuracy of acoustic measurement results. However, for the whole sea area, the construction of global ocean sound velocity field and the construction of seamless vertical datum still need to be solved.
In order to realize high-precision and high-resolution acquisition of global seabed topography, the following difficult problems need to be broken through in the future:
(1) Theory and model of acoustic seabed reflection
(2) The whole sea area seabed topography inversion technology based on wide scanning amplitude and large area side scanning sonar images;
(3) The theory and method of constructing the global sound velocity field model
(4) Refinement theory and method of global tidal model
(5) Theory and method of constructing seamless vertical datum model of global ocean
(6) Global Stereo Bathymetry Technology
(7) Multi-source sounding data fusion technology and global seabed topography acquisition
(8) Establishment of Domestic Series Sounding Data Processing Platform System
Strategic significance: (Briefly introduce the major influence and leading role on the scientific and technological development in this field or other related cross-cutting fields after the breakthrough of this issue, as well as the possible major scientific and technological, economic and social benefits)
(1) A major change in the field of bathymetry: it will significantly improve the accuracy, resolution and operation efficiency of seabed topography acquisition, provide a brand-new way to acquire global seabed topography and geomorphology information, and make China's marine bathymetry technology one of the forefront in the world.
(2) Form a relatively complete theory and method system of geometric ocean geodesy: make up for the incompleteness of the theoretical system of geometric geodesy in ocean vertical datum, and provide high-precision absolute reference datum and instantaneous absolute starting datum for global offshore operations.
(3) Provide theoretical and methodological support for the research and development of marine survey equipment: The formed theoretical methods support the research and development of large sweep width, high precision, high resolution and independent marine survey equipment to fill the gap in China.
(4) Fill in the large gap of China's global seabed topography, solve the problem that the goal cannot guarantee "going out and going far", and provide basic guarantee for the implementation of China's "marine power strategy".