Research On Principle And Data Processing Methods Of Airborne Laser Bathymetric Technique

Airborne laser bathymetric technique is a hot and difficult problem in the field of present marine surveying and mapping. The promising prospect of the application of the technique has greatly attracted people's attention. With the maturing of bathymetric hardware in foreign countries, and the solution of many key problems on hardware and system integration, many organizations and consortiums have obtained enormous ocean observations using bathymetric system and applied the system into a lot of fields. However, the post processing methods of bathymetric observations are still in the phase of research and development, and there are still many problems that have not been well solved. Under such background, the dissertation performed research on some key problems of airborne laser bathymetric system (ALBS). The main work completed is as follows.(1) The history and development of Airborne Laser Bathymetry (ALB) technology as well as the current status of ALB data processing techniques were summarized in general. The development of ALB technology in the world within four periods was introduced in detail, and the major problems and challenges faced by ALB especially the data processing techniques were illustrated. Then the work scheme and target of the dissertation were briefed.(2) Mathematical models for ALB computations and bathymetric capability assessment were presented on the basis of the system structure and work mechanism of ALB. Through a detailed analysis of the characteristics of ALB signal transmission, a computation method for the determination of the summit position of ALB laser echo signal using invariant moment was proposed, and the method for shift correction of seabed echo signal using translating moment translation was also proposed. By simulating the reflection signal from seabed using Gauss Function, the variation of the amplitude of seabed reflection signal with the control parameter of spectral width was researched, and the function model of the optimal truncation frequency of laser bathymetric FIR and the spectral control parameter was set up, and thus the optimal filter of laser echo signal was designed. As a result, the effective recognition and extraction of laser pulse echo signal were implemented with shipboard test data.(3) The computation model for dynamic differential GPS was derived, based on which the new idea that applied the Precise Point Positioning (PPP) technique to the positioning and orientation of ALB was put forward, and the mathematical model for PPP was derived, and the PPP solution method using conventional solution was presented, and furthermore the technical approaches to some key problems of the application of the method were provided. The scheme for the improvement of INS/GPS integrated navigation system as well as the calibration and transferring-and-alignment method for the inertial measuring unit were also presented. Using navigation positioning observations from airborne gravimetry and state-of-the-art software, numerical tests were made on the applicability and computation model of the above three positioning and orientation methods, from which some beneficial conclusions were drawn, which lays the foundation for future engineering applications.(4) The processing method for encoder cycle and laser pulse record was presented on the basis of the principle on which the pulse-type laser emitter works. The coordinate systems for different sensor observations were defined and the transformations between the systems were determined, and then the integration and synchronous processing method for multi-source observations from ALB, GPS and electronic compass was proposed. A method was given for the determination of the incidence points at sea surface and seabed by computing the projections of the reflector normal and reflected laser beams onto device planes, and the strict model for the computation of the incidence point coordinates on sea surface was derived in detail. Simulation and actual observations processing effectively demonstrated the applicability and correctness of the proposed methods.(5) Error sources that have effect on the observations of ALB were given through a thorough analysis, and the effects of different error sources on ALB were discussed from a quantitative and a qualitative view respectively. The three computation models for the reduction and correction of depths from ALB were given material analyses, from which the conclusion that the inertial navigation aided correction model is the most preferred scheme of the three models. Then, aiming at the characteristics that more outliers than common appears in ALB, the outlier detection method based on weight-selection iteration of robust M-estimation, along with the judgment model and computation flow for outlier detection was brought forward. According to the requirement that for the stripe conjunction of ALB there must be some overlapped area, the trend surface model that suits ALB data system bias was provided, and the two-step method was recommended to solve the system bias compensation within the ALB observations, which greatly simplifies the fusion process of ALB stripe data.(6) The technique and processing steps for the back-check of ALB data quality using single beam bathymetric data were proposed, which were implemented on the ALB system developed by China. The results for the exterior check of the system were given from experiments at sea. To overcome the prominent systematic bias between the two bathymetric techniques, a new processing scheme was proposed for making corrections and compensations to the systematic bias of ALB data with single beam bathymetric data as control.