Dr. Kevin Repasky
Assistant Professor, Electrical & Computer Engineering Department
Montana State University
“Development of an eye-safe diode laser based micro-pulse differential absorption lidar (DIAL) for water vapor and aerosol profiling in the lower troposphere”
Abstract: Researchers at Montana State University (MSU) are developing a set of lidar
instruments for remote sensing aerosol studies. Instrument in various stages of development
at MSU include a multi-wavelength backscatter lidar, a high spectral resolution lidar, a
differential absorption lidar (DIAL) for spatially mapping carbon dioxide, and an eye-safe diode
laser based DIAL for water vapor and aerosol profiling. This talk will mainly focus on the
development of the diode laser based water vapor DIAL.
The diode laser based water vapor DIAL utilizes two external cavity diode lasers (ECDL),
one locked to the on-line wavelength and the other locked to the off-line wavelength, to
injection seed a tapered semiconductor optical amplifier (TSOA). The output of the TSOA is
pulsed by pulsing the drive current to the TSOA producing up to 7 μJ of pulse energy over a 1
μs pulse duration with pulse repetition frequencies up to 10 kHz. The scattered light is
collected using a commercial 35 cm Schmidt-Cassegrain telescope with the collected light
launched into a multi-mode optical fiber. The return signal is monitored using an avalanche
photodiode (APD) and a multichannel scalar card. The off-line channel of the DIAL is
calibrated using the Rayleigh scattered returns above the boundary layer and the aerosol
backscatter and extinction properties are retrieved using the Fernald lidar inversion technique
and an independent measurement of the aerosol optical depth. Water vapor number density
profiles are retrieved using both the on-line and off-line returns and the DIAL equation.
Recent observational studies using multiple instruments including the water vapor DIAL will
be presented. During this seven day observational period, a rapid transition from a low aerosol
optical depth to higher aerosol optical depth resulting from advected biomass burning aerosols
due forest fire smoke occurred. The characterization of the aerosol optical properties and
resulting aerosol direct effect radiative forcing will be presented.
Thurday, April 14, 2011, 2:30 p.m.
FL-2 Main Seminar Room
Wine & Cheese Reception after Keynote