Research On Photon Counting Lidar Bathymetric Data Processing Method

Airborne laser bathymetric technology is an active remote sensing technology that can acquire 3D point clouds of underwater and underwater targets with high accuracy and high efficiency,and has become one of the popular applications of shallow water bathymetry.With the increasing demand for laser bathymetry,there are many limitations in the measurement of traditional linear detection lidar due to its detector sensitivity,power consumption and weight.The introduction of time-corrected singlephoton counting technology into the photon counting lidar greatly improves the time measurement resolution and detection sensitivity of the system,and reduces the requirements for laser pulse energy.It can realize light,small and low power consumption,adapt to the rapid and exciting mapping of unmanned aerial vehicle,and has great advantages and potential in the fields of shallow water deep measurement,intertidal beach mapping,etc.In the aspect of lidar bathymetric data processing,the bathymetric data of traditional linear detection lidar is to record the echo waveform signal of laser pulse in the whole transmission process,and the echo intensity in the waveform data directly represents the amplitude value of laser energy.The processing of traditional lidar sounding data is to decompose the echo signals of water surface and bottom from the waveform data.As to realize the inversion of water depth.Due to the different detection mechanism,the bathymetric data of photon counting lidar is the photon event signal that the detector responds to,and there is no intensity information in a single pulse,so it can not directly decompose the water surface and underwater echo.Therefore,the data processing method is different from the waveform data processing method,it is necessary to carry out statistical analysis on multiple pulses to extract the water surface and underwater signal.In addition,the water surface signal detected by 532 nm laser is actually the linear superposition of the scattering signal of particles in the air-water interface and the thin water layer under the interface,so it is difficult to determine the water surface signal,and the water body has a strong attenuation to the laser,and the intensity of the underwater signal is usually weak,so it is difficult to identify the underwater signal.The photon counting lidar relies on its high detection sensitivity and efficiency.It can make the best use of the energy of each photon in the laser echo to detect the weak signal.Up to now,there is no uniform standard for the processing of sounding data in photon counting lidar.In this paper,the processing methods of the sounding data of the domestic light and small photon counting lidar are studied.This study covers following topics:(1)This paper analyzes the basic principle of time-corrected single-photon counting and photon counting laser bathymetry,introduces the system composition,working scheme,optical structure and relevant performance indexes of domestic light and small photon counting laser radar,and expounds the system design of light and small,low power consumption.With high detection sensitivity,it can be used to detect the water depth in the intertidal zone with complex environment.(2)The geometric imaging mode of elliptical scanning structure is analyzed,and the coordinate derivation of the underwater and underwater laser foot points in the sensor coordinate system is completed,as well as the conversion from the sensor coordinate system to the GPS geodetic coordinate system is completed by combining the position and attitude parameters collected by high-precision POS,and finally the 3D point cloud solution of photon counting lidar is realized by analyzing the geometric imaging model The systematic errors in the construction have great influence on the scanning angle error and ranging error of the sensor coordinate system.The angle calibration method of the collimator and the distance calibration method of the outdoor fixed target plate are used respectively,and the corresponding correction model is given.The experimental results also verify the feasibility of the calibration method and the accuracy of the geometric imaging model.The mean square error of the angle calibration residual is 0.085° and the RMS error of the distance calibration is 0.0279 m.(3)The detection probability model of photon counting lidar sounding signal is studied.By analyzing the transmission process and echo characteristics of photon counting lidar in water depth detection,the echo intensity of the echo signal of photon counting lidar is discussed in detail.The average photoelectron number is used to represent the echo intensity of photon counting lidar.The influence of different laser energy on the echo intensity is simulated,and the echo of the echo signal in different environment is simulated the relationship between echo intensity and detection probability is established,which provides theoretical support for effective recognition of sounding signal.(4)The data processing method of photon counting lidar sounding is designed,the indoor static experiment and airborne sounding experiment are carried out,and some valuable data are obtained.In the indoor static experiment,k-nearest neighbor algorithm is introduced into the photon event signal filtering,and histogram derivative detection method is used to automatically identify the sounding signal,as to achieve the purpose of water depth detection,and verify the detection probability model and simulation analysis results.In the airborne sounding experiment,in order to obtain the actual effect of the method in this paper,aiming at the lidar data in the intertidal zone,based on the above data processing methods,a method of using different polarization channels to assist in identifying the water surface and underwater signals is designed,and finally the solution of the three-dimensional point cloud above and under the water in this area is realized.