Calibration of a high spectral resolution lidar using a Michelson interferometer, with data examples from ORACLES

Area of Science:

• Atmospheric Science
• Remote Sensing
• Lidar Technology

Background:

• The NASA Langley airborne High Spectral Resolution Lidar (HSRL-2) utilizes a Michelson interferometer for atmospheric profiling.
• Accurate retrieval of aerosol optical properties relies on precise separation of molecular and particulate backscatter.
• The contrast ratio of the interferometer is a key parameter influencing retrieval accuracy.

Purpose of the Study:

• To present retrieval equations for High Spectral Resolution Lidar (HSRL) data that account for imperfect channel separation.
• To analyze the impact of contrast ratio accuracy on the retrieval of backscattering and extinction coefficients.
• To demonstrate the application of HSRL-2 data from the ORACLES field campaign for characterizing biomass burning aerosols.

Main Methods:

• Development of retrieval algorithms incorporating incomplete separation of molecular and particulate backscatter.
• Analysis of error propagation from contrast ratio uncertainty to optical property retrievals.
• Application of the HSRL-2 instrument aboard the NASA ER-2 aircraft during the ORACLES field campaign.

Main Results:

• Underestimating the interferometer's contrast ratio leads to larger errors in optical property retrievals compared to overestimation.
• Smaller true contrast ratios and more extreme aerosol loading critically increase retrieval errors.
• Analysis of biomass burning smoke aerosols revealed distinct optical properties in adjacent layers, consistent with particle size differences.

Conclusions:

• A high and stable contrast ratio is essential for precise backscatter and extinction retrievals using HSRL-2.
• The developed retrieval equations provide a more accurate method for analyzing HSRL data, especially in complex aerosol conditions.
• HSRL-2 measurements effectively characterize the optical properties of biomass burning aerosols, aiding in understanding their climate impact.