Noise Reduction in White Light Lidar Signal Using a One-Dim and Two-Dim Daubechies Wavelet Shrinkage Method

Toshihiro Somekawa,Masayuki Fujita,Maria Cecilia D Galvez,Chihiro Yamanaka,Edgar A Vallar

doi:10.4236/ars.2013.21002

Abstract

A 1-D and 2-D Daubechies 5 (db5) discrete wavelet shrinkage methods using a 10 level decomposition was applied to white light lidar data particularly at 350 nm and 550 nm backscattered signal. At 350 nm, the backscattered signal is very weak as compared to 550 nm backscattered signal because of the spectral intensity distribution of the generated white light. The 1-D and 2-D wavelet shrinkage method gave a much better result as compared with the moving average method. However, the 2-D wavelet shrinkage method produced a much better denoised lidar signal compared with the 1-D wavelet shrinkage method. This is indicated by the 142% increase in correlation coefficient between the 2-D denoised lidar signal and the 800 nm original lidar signal as compared with only 12% increase in correlation coefficient for the 1-D denoised lidar signal. The 2-D wavelet shrinkage method also gave a much higher SNR value of 65.9 compared to 1-D which is 38.8.

Highlights

Supercontinuum generation on air and other gas media using high peak power femtosecond lasers opened the way for multispectral atmospheric remote sensing using a white light lidar
A 1-D and 2-D Daubechies 5 discrete wavelet shrinkage methods using a 10 level decomposition was applied to white light lidar data at 350 nm and 550 nm backscattered signal
We have demonstrated that the coherent white light continuum can be used for depolarization and multiwavelength measurement in the same way as the conventional lidar [3]

Summary

Introduction

Supercontinuum generation on air and other gas media using high peak power femtosecond lasers opened the way for multispectral atmospheric remote sensing using a white light lidar. We have demonstrated that the coherent white light continuum can be used for depolarization and multiwavelength measurement in the same way as the conventional lidar [3]. Multi-wavelength lidar observations for conventional lidar often use at least two laser sources. The multi-wavelength lidar measurements using a coherent white light continuum have the capability of obtaining the wavelength dependence of the backscatter coefficients of aerosols, which can be used to evaluate the particle size distribution using one laser source [1]. The signals are usually buried in noise, depending on the power of the laser and the observed altitude. Lidar signals with noise can be improved by moving average method. The moving average method only smoothen the signals and does not remove specky values especially the negative values produced by noises [4]. Since the WT has different resolutions on noise and signal, it can perform denoising process on lidar signal

Denoising Algorithm

Experimental Results and Discussion

Conclusion