Comparison of multichannel signal deconvolution algorithms in airborne LiDAR bathymetry based on wavelet transform

Airborne LiDAR bathymetry offers low cost and high mobility, making it an ideal option for shallow-water measurements. However, due to differences in the measurement environment and the laser emission channel, the received waveform is difficult to extract using a single algorithm. The choice of a suitable waveform processing method is thus of extreme importance to guarantee the accuracy of the bathymetric retrieval. In this study, we use a wavelet-denoising method to denoise the received waveform and subsequently test four algorithms for denoised-waveform processing, namely, the Richardson–Lucy deconvolution (RLD), blind deconvolution (BD), Wiener filter deconvolution (WFD), and constrained least-squares filter deconvolution (RFD). The simulation and measured multichannel databases are used to evaluate the algorithms, with focus on improving their performance after data-denoising and their capability of extracting water depth. Results show that applying wavelet denoising before deconvolution improves the extraction accuracy. The four algorithms perform better for the shallow-water orthogonal polarization channel (PMT2) than for the shallow horizontal row polarization channel (PMT1). Of the four algorithms, RLD provides the best signal-detection rate, and RFD is the most robust; BD has low computational efficiency, and WFD performs poorly in deep water (< 25 m).

Comparison of Multichannel Signal Deconvolution Algorithms in Airborne LiDAR Bathymetry Based on Wavelet Transform

Airborne LiDAR bathymetry offers low cost and high mobility, making it an ideal option for shallow-water measurements. However, due to differences in the measurement environment and the laser emission channel, the received waveform is difficult to extract using a single algorithm. The choice of a suitable waveform processing method is thus extremely important to guarantee the accuracy of the bathymetric retrieval. In this work, we use a wavelet-denoising method to denoise the received waveform and then test four algorithms for denoised-waveform processing: Richardson–Lucy deconvolution (RLD), blind deconvolution (BD), Wiener filter deconvolution (WFD), and constrained least-squares filter deconvolution (RFD). The simulation database and the measured multichannel database are used to evaluate the algorithms, with the focus on improving their performance after the data-denoising preprocessing and their capability of extracting water depth. The results show that applying wavelet denoising before deconvolution improves the extraction accuracy. The four algorithms perform better for the shallow water orthogonal polarization channel (PMT2) than the shallow horizontal row polarization channel (PMT1). Of the four algorithms, RLD provides the best signal-detection rate, and RFD is the most robust. BD has low computational efficiency, and WFD performs poorly in deep water (<25 m).

The Benefit of the Geospatial-Related Waveforms Analysis to Extract Weak Laser Pulses

Waveform lidar provides both geometric and waveform properties from the entire returned signals. The waveform analysis is an important process to extract the attributes of the reflecting surface from the waveform. The proposed method analyzes the geospatial relationship between the return signals by combining the sequential waves. The idea of this method is to analyze the waveform parameters from sequential waves. Since the adjacent return signals are geospatially correlated, they have similar waveform properties that can be used to validate the correctness of the extracted waveform parameters. The proposed method includes three major steps: (1) single-waveform processing for the initial echo detection; (2) multi-waveform processing using waveform alignment and stacking; (3) verification of the enhanced weak return. The experimental waveform lidar data were acquired using Leica ALS60, Optech Pegasus, and Riegl Q680i. The experimental result indicates that the proposed method successfully extracts the weak returns while considering the geospatial relationships. The correctness and increasing rate of the extracted ground points are related to the vegetated coverage such as the complexity and density. The correctness is above 76% in this study. Because the nearest waveform has a higher correlation, the increase in distance of adjacent waveforms will reduce the correctness of the enhanced weak return.