Feasibility Study of Airborne HSRL Temperature Profiling for Retrievals of the Planetary Boundary Layer Height

The Planetary Boundary Layer Height (PBLH) is a critical atmospheric parameter for analysis of surface air quality, particularly for understanding vertical mixing of aerosols and trace gases, and for improved short term weather forecasting. Airborne lidar measurements of the vertical gradient in aerosols provide a convenient way to obtain this parameter but often fail to provide reliable PBLH estimates in regions with complex vertical variability or high spatial changes such as water-land transitions or regions of heavy free tropospheric aerosol loading. Measurements of temperature gradients (i.e. inversions) have been shown to offer valuable additional information for the derivation of PBLH. However, current airborne remote sensing temperature measurement techniques lack the spatiotemporal resolution and/or range desired for understanding air quality in metropolitan areas. This work aims to assess the feasibility of adding temperature profiling capability to NASA LaRC’s first generation airborne aerosol and ocean profiling instrument, HSRL-1.

The temperature high spectral resolution lidar (HSRL) technique relies on the Doppler broadening of the molecular scattering signal. Our approach looks to leverage the current HSRL-1 instrument and data acquisition infrastructure, particularly its flight-proven laser, receiver, and detectors, and exploits the strong signal strength of elastic scattering. This work combines simulated transmission spectra of narrow band filters, performance information of HSRL-1 hardware, and signal-to-noise levels from previous airborne field campaigns to determine both the optimal instrument configuration and the expected performance. The modeling portion of this study can be applied to any HSRL operating near 532 nm (2^nd harmonic of the Nd:YAG or Nd:YVO₄ lasers) and highlights the challenges of active temperature profiling over spatiotemporal scales relevant to a variety of science applications. The use of previous flight data both provides a more accurate representation of system performance and allows for a proper weighting of signal strength and temperature sensitivity. Other temperature lidar methods will be included for comparison. Additionally, instrument complexity and systematic error sources will also be considered as they relate to determining the PBLH.