High-Spectral-Resolution Lidar with Iodine-Vapor Filters: Measurement of Atmospheric-State and Aerosol Profiles

Abstract

A high-spectral-resolution lidar can measure vertical profiles of atmospheric temperature, pressure, the aerosol backscatter ratio, and the aerosol extinction coefficient simultaneously. We describe a system with these characteristics. The transmitter is a narrow-band (FWHM of the order of 74 MHz), injection-seeded, pulsed, double YAG laser at 532 nm. Iodine-vapor filters in the detection system spectrally separate the molecular and aerosol scattering and greatly reduce the latter (-41 dB). Operating at a selected frequency to take advantage of two neighboring lines in vapor filters, one can obtain a sensitivity of the measured signal-to-air temperature ratio equal to 0.42%/K. Using a relatively modest size transmitter and receiver system (laser power times telescope aperture equals 0.19 Wm(2)), our measured temperature profiles (0.5-15 km) over 11 nights are in agreement with balloon soundings to within 2.0 K over an altitude range of 2-5 km. There is good agreement in the lapse rates, tropopause altitudes, and inversions. In principle, to invert the signal requires a known density at one altitude, but in practice it is convenient to also use a known temperature at that altitude. This is a scalable system for high spatial resolution of vertical temperature profiles in the troposphere and lower stratosphere, even in the presence of aerosols.

NASA LaRC airborne high spectral resolution lidar aerosol measurements during MILAGRO: observations and validation

“…The raw HSRL data are averaged over 100 shots (0.5 s at 200 Hz) temporally with 30 m vertical bins, which are analyzed to determine aerosol extinction, backscatter, and depolarization. The HSRL technique is employed for the 532 nm wavelength, utilizing the iodine vapor filter technique (Hair et al, 2001(Hair et al, , 2008Piironen et al, 1994). The received 532 nm backscatter return is split between three optical channels: (1) one measuring the backscatter (predominantly aerosol) polarized orthogonally to the transmitted polarization, (2) one measuring 10% of the molecular and aerosol backscatter polarized parallel to the transmitted polarization, and (3) one passing through an iodine vapor cell which absorbs the central portion of the backscatter spectrum, including all of the Mie backscatter, and transmits only the Doppler/pressure-broadened molecular backscatter.…”

“…Deployed from aircraft, lidars are capable of mapping vertical distributions of aerosol over large spatial regions in a relatively short amount of time -something that is not possible with in-situ instruments. Unlike the standard elastic backscatter technique, the High Spectral Resolution Lidar (HSRL) technique accurately measures the vertical profile of aerosol extinction without reliance on an external measurement of aerosol optical depth (AOD) (McGill et al, 2003) or assumptions of the aerosol extinction-to-backscatter ratio (Hair et al, 2001(Hair et al, , 2008Cattrall et al, 2005) to constrain the extinction retrieval.…”

1064 nm rotational Raman lidar for particle extinction and lidar-ratio profiling: cirrus case study

“…The particle extinction coefficient is one of the key parameters in the description of the impact of clouds and aerosols on environmental, weather, and climate processes, and in the retrieval of microphysical properties of the detected cloud and aerosol layers. Two different lidar techniques are available for the measurement of aerosol and cloud extinction profiles, the Raman lidar method (Ansmann et al, 1990(Ansmann et al, , 1992aAnsmann and Müller, 2005) and the High Spectral Resolution Lidar (HSRL) technique (Shipley et al, 1983;Grund and Eloranta, 1990;Hair et al, 2001;Eloranta, 2005). An HSRL is measuring strong Rayleigh backscatter signals so that likewise short signal averaging periods are sufficient to retrieve high-quality extinction profiles.…”

Exploration of Whole Atmosphere Lidar: Mach-zehnder Receiver to Extend Fe Doppler Lidar Wind Measurements from the Thermosphere to the Ground

“…Therefore, after summation, the same resonance Doppler lidar techniques for retrieving wind and temperature in the MLT region are still valid. Unlike many other techniques that may discard a portion of the backscatter [4], [5], [12], the MZI techniques, by recovering the complete spectrum, enable a single receiver to profile wind and temperature through the complete atmospheric column with nearly the same precision as the original instrument and without modification to any existing retrieval techniques.…”