Development of Airborne LiDAR Bathymetric Technology and Application
Significance With approximately 71％of the earth's surface covered by seawater,the marine environment is closely linked to global climate change,the evolution of ecosystems,and the global carbon cycle,among other activities.In recent years,in particular,the increasingly close connection between oceans and human activities,along with the significant impact of human activities on the global marine environment,has sparked considerable interest in understanding the oceans.This interest has led to the development of a wide range of methods and equipment for exploring the oceans.Mainstream programs for ocean exploration research primarily include acoustic and optical programs.Acoustic solutions,such as multibeam sounders,single-beam sounders,and side-scan sonars,are commonly used in ocean exploration.However,because of the substantial difference in viscosity coefficients between water and air,the acoustic impedance values near the air-sea interface vary significantly.Moreover,when an acoustic signal propagates between air and water,it undergoes significant reflection,thereby affecting its propagation in both directions.This limits the application of acoustic oceanographic equipment to submerging below the surface of water and using shipboard platforms.Coastal zones and shallow water areas of sea islands and reefs are the areas where the interaction between sea and land is frequent,and also the areas where human beings participate most in marine activities.Because of the shallow water depth and complex underwater topography in these areas,traditional shipborne multibeam and single-beam sonar surveys are characterized by operational hazards,low efficiency,and high collection costs,resulting in numerous gaps in large-scale mapping data in the shallow waters of China's coastal zones and sea islands and reefs.Compared to passive remote sensing,airborne LiDAR bathymetric technology,as an optical means of active detection,can function continuously and acquire ocean profile information.This technology uses the good seawater penetration characteristics of the blue-green band laser.It transmits the laser from an airborne platform and receives the laser echo from both the sea surface and seabed,thus realizing shallow-water measurement.Simultaneously,it can also measure the elevation of the land surface.After approximately 60 years of development and application,airborne LiDAR bathymetric technology has demonstrated advantages including high efficiency,high accuracy,high mobility,and low cost in near-shore shallow-water areas with suitable water quality conditions.This technology has become the preferred means of integrated surveying and mapping of land and sea in these regions.With the advancements in laser and unmanned aerial vehicle(UAV)technologies,existing research results should be summarized and the future development of airborne LiDAR bathymetric systems should be discussed.Progress First,the principle of airborne LiDAR bathymetric system is introduced,and studies on system composition and data processing methods are discussed.Subsequently,key technological developments such as the blue-green laser source,large dynamic range optical reception,and high-speed data acquisition are analyzed.The parameters of typical airborne laser bathymetric systems,such as HawkEye-5,CZMIL,and Mapper10K,are compared(Tables 1 and 2).Thereafter,new technological developments in airborne laser bathymetric systems,including photon counting laser bathymetric systems and multi-wavelength laser ocean sounding systems,are introduced.The photon-counting laser bathymetric system developed by the Shanghai Institute of Technical Physics(SITP)was tested in Qiandao lake,Zhejiang province,achieving a 3.1 m water depth measurement(approximately two times the depth of the transparency disk)(Fig.24).The Shanghai Institute of Optics and Fine Mechanics(SIOM)developed an underwater multi-wavelength ocean detection LiDAR and conducted experiments on the spectral detection of different ores underwater.They also investigated classification algorithms in the laboratory(Fig.31).Typical applications of airborne LiDAR bathymetric systems are then presented,encompassing four aspects:integrated topographic mapping of land and sea,remote sensing observation of ocean waves,three-dimensional remote sensing observation of optical parameters of seawater,and substrate classification.Conclusions and Prospects Airborne LiDAR bathymetric technology and its applications have matured,and existing systems can satisfy the demand for integrated large-scale surveying and mapping of land and sea.The future development trend will be towards system miniaturization and unmanned platforms.Technologies that can combine photon counting and waveform sampling,high-efficiency broad-spectrum laser technologies in the blue and green bands,the technology that can generate data by combining simulation and actual measurement,and processing methods handling considerable amounts of data should be developed.
airborne LiDAR bathymetryphoton countingmulti-wavelength laserclassification of land and sea waveformecho extractionslant range correction
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