Ground Based Demonstration of an Airborne High Spectral Resolution Temperature Profiling Lidar

There is a strong desire for improved airborne thermodynamic profiling capabilities, particularly within the planetary boundary layer. While active temperature profiling lidars using rotational Raman scattering and differential oxygen absorption (DIAL) exist for ground-based use, these techniques are limited by the inefficiency of Raman scattering and oxygen DIAL’s need for collocated water vapor and aerosol measurements. This work aims to investigate the sensitivities and signal-to-noise of a temperature high spectral resolution lidar (HSRL) measurement approach for airborne tropospheric temperature profiling and add this capability to the NASA LaRC first generation airborne aerosol and profiling instrument, HSRL-1.

The temperature HSRL technique relies on the thermally sensitive Doppler broadening of the Rayleigh scattering signal. In an aerosol HSRL, a spectral notch filter is used to differentiate between molecular and aerosol backscattering. The addition of a second molecular channel (using a second notch filter with a distinct transmission spectrum) enables an observation dependent on the molecular scattering spectral lineshape (i.e. temperature and pressure) and independent of aerosol scattering. The implementation of an additional channel to the HSRL-1 instrument leverages the current HSRL-1 instrument and data acquisition infrastructure, particularly the flight-tested Nd:YVO4 laser, receiver, and detectors, and exploits the strong signal strength of elastic scattering, resulting in a measurement well suited for the moving, airborne platform.

This presentation will cover the temperature HSRL retrieval technique and discuss the theoretical optimization and experimental characterization of the required HSRL-1 system modifications. The reconfigured system has been operated in a ground-based, zenith-pointing configuration to test the new thermal profiling capability. A set of these results will be examined and compared to co-located radiosonde measurements. Additionally, the expected airborne performance, which has been simulated using signal levels from previous HSRL-1 field deployments, will be presented.