Validation of New Methods in Inferring Extinction and Lidar Ratio from Photon-Limited Lidar Observations

Validation of new methods in inferring extinction & lidar ratio from photon limited lidar observations

Authors: Willem J. Marais, Robert E. Holz, Edwin W. Eloranta and Rebecca M. Willett

Atmospheric lidar observations provide a unique capability to directly observe the vertical column of cloud and aerosol scattering properties. Detector and solar-background noise, however, hinder the ability of lidar systems to provide reliable backscatter and extinction cross-section estimates. The work of this abstract leverages methods originally developed for medical imaging systems that have similar physics to lidar remote sensing. Our ultimate goal is to modify and improve these techniques to develop inversion algorithms for space-based lidar systems to accurately infer the extinction and lidar ratio while maintaining the high spatial and temporal resolution of the measurements.

We started our research with developing inversion algorithms for the UW-Madison High Spectral Resolution Lidar (HSRL) system; Figure 1 shows an example of an inversion result from our new method, coined Poisson Total Variation (PTV), applied to an elevated aerosol layer juxtaposed against the inversion result of the standard HSRL inversion method. From Figure 1 it is clear that estimates of the PTV method not only has less residual noise compared to that of the standard method, but the PTV method is able to infer the extinction, depolarization ratio and lidar ratio at higher spatial and temporal resolutions while significantly reducing the noise; it has been demonstrated quantitively via realistic simulations that the PTV method infers the extinction, depolarization ratio and lidar ratio more accurately compared to the standard method (Marais, 2017; Marais et al., 2016).

In our talk we will describe the PTV method and present progress that we have made in further validating the PTV method by processing more than a month of HSRL observations that were acquired during the KORUS-AQ campaign; the validation procedure involves comparing the PTV and standard method inversion results of temporal and spatial uniform scenes where the standard method is known to provide accurate estimates. We will also demonstrate the ability of the PTV method to accurately infer high spatial and temporal resolution extinction, depolarization ratio and lidar ratios by presenting the uncertainties of these inferred parameters. Finally, we will report on the progress we have made in adapting our new inversion methods for space based lidar systems.

References

Marais, W.J., Holz, R.E., Hu, Y.H., Kuehn, R.E., Eloranta, E.E. and Willett, R.M., 2016. Approach to simultaneously denoise and invert backscatter and extinction from photon-limited atmospheric lidar observations. Applied optics, 55(29), pp.8316-8334.

Marais, W.J., 2017. Poisson Inverse and Denoising Problems in Atmospheric Lidar Imaging. The University of Wisconsin-Madison.