Sea-bottom Echo Signal Extraction Technology For Airborne Bathymetry Lidar

Airborne laser bathymetry technology has become a hot topic of researchers in various countries because of its flexibility,speed and accuracy,and gradually replace the traditional method of water depth measurement.It plays a very important role in water depth survey and underwater topography mapping in river and near sea area.This paper will further study the key technology of echo signal processing in airborne laser bathymetry.The sea-bottom echo signal in the echo signal is extracted,and the peak of the sea-surface echo signal and the sea-bottom echo signal in the echo signal are clearly identified by the data processing.Because of the influence of various algae and suspended solids in sea water,the initial echo data of airborne lidar system contain a lot of interference signals.By comparing two kinds of digital filters——infinite impulse response(IIR)filter and finite impulse response(FIR)filter,it is found that the FIR filter system is more stable,more efficient and simpler in design.Therefore,in this paper,using the FIR filter to eliminate the initial echo signal interference signal.And the filtering effect of FIR filter with different design methods is analyzed and compared in detail.On this basis,after smoothing the judgement of filtered data,this paper selects the best filtering effect and stores this data after smoothing.After filtering,echo data of airborne laser bathymetric system is another focus of this paper.because the data is discrete,it is necessary to choose the appropriate fitting method to fit the discrete data.In this paper,the segmented fitting method is used to divide the echo signal intothree parts: the sea-surface echo signal,the sea backscatter signal and the sea-bottom echo signal.The least squares fitting method and multiple function fitting method are used to fit the discrete data of the three parts respectively.The fitting effect of the two method is analyzed and compared,and the error analysis is carried out.Three fitting functions with the best fitting effect in the multi function fitting method and three fitting functions in the least squares fitting method are spliced respectively,and the complete echo signal data of the ocean sounding part in the filtered airborne laser bathymetry system are fitted with the fitting function after the splicing.The fitting effect of the two fitting methods is compared,and error analysis is carried out to ensure that the peak location of the sea-surface echo signal and the sea-bottom echo signal can be clearly distinguished.