An assessment of a software simulation tool for lidar atmosphere and ocean measurements

Abstract:

A high-fidelity lidar simulation tool is used to generate synthetic lidar backscatter data that closely matches the expected performance of various lidars, including the noise characteristics inherent to analog detection and uncertainties related to the measurement environment. This tool supports performance trade studies and scientific investigations for both the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), which flies aboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and the NASA Langley Research Center airborne High Spectral Resolution Lidar (HSRL). CALIOP measures profiles of attenuated backscatter coefficients (532 and 1064 nm) and volume depolarization ratios at 532 nm. HSRL measures the same profiles plus volume depolarization at 1064 nm and a molecular-only profile which allows for the direct retrieval of aerosol extinction and backscatter profiles at 532 nm. The simulation tool models both the fundamental physics of the lidar instruments and the signals generated from aerosols, clouds, and the ocean surface and subsurface. This work presents the results of a study conducted to verify the accuracy of the simulated data using data from both HSRL and CALIOP. The tool was tuned to CALIOP instrument settings and the model atmosphere was defined using profiles of attenuated backscatter and depolarization obtained by HSRL during underflights of CALIPSO. The validated HSRL data provide highly accurate measurements of the particulate intensive and extensive optical properties and thus were considered as the truth atmosphere. The resulting simulated data were processed through the CALIPSO data analysis system. Comparisons showed good agreement between the simulated and CALIOP data. This verifies the accuracy of the tool to support studies involving the characterization of instrument components and advanced data analysis techniques. The capability of the tool to simulate ocean surface scattering and subsurface profiling has been used to guide the design of future airborne and satellite ocean-profiling lidars. Initial comparisons of simulated signals with ocean lidar profiles acquired on the Ship-Aircraft Bio-Optical Research (SABOR) experiment are being used to validate this new ocean-profiling measurement capability.