The characterization of atmospheric aerosol scattering properties, particularly in the troposphere, is of critical importance in assessing the global-scale wind measurement capabilities of Earth-orbiting Doppler lidar. This activity was therefore initiated in the 1980s in response to the then prevailing lack of knowledge concerning the optical and infrared properties of tropospheric aerosols, particularly outside of the industrially developed regions of the northern hemisphere.
The long-term study of atmospheric aerosol backscatter and extinction in the 9-11 µm spectral region has been in process at JPL since 1984 for the assessment of long-term trends, the impact of major volcanic eruptions on the atmospheric aerosol loading and the associated atmospheric transmittance, seasonal influences on the aerosol sources and sinks, and the elucidation of backscatter statistical properties. The image below depicts the observed mid-infrared integrated backscatter from the free troposphere (upper panel) and the lower stratosphere (lower panel) column above the JPL Pasadena site since the eruption of the Philippine volcano Mt. Pinatubo in June of 1991:
Boundary layer backscatter and attenuation profiles associated with the corresponding vertical profiles have been routinely recorded throughout the extent of the database collection activity. A multiyear time series of this data is shown in the figure below. Comparison of these data against local PM10 particulate records has revealed similarities in general trends during the last decade as stringent air quality regulations have resulted in significant reductions in anthropogenic aerosol generation.
The decline in boundary layer aerosol loading evident since 1990 (traced by the orange trend line in the above display) is matched by a corresponding decrease in ozone levels within the Los Angeles Basin over the same interval.
The ground-based lidar is also used in studies of ephemeral phenomena, such as the major Asian dust event of April, 1998, and is currently participating in correlative validation activities for the Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard the EOS Terra spacecraft.
References
D. M. Tratt and R. T. Menzies: Recent climatological trends in atmospheric aerosol backscatter derived from the Jet Propulsion Laboratory multiyear backscatter profile database. Appl. Opt., 33(3), 1994, 424-430.
R. T. Menzies and D. M. Tratt: Evidence of seasonally dependent stratosphere-troposphere exchange and purging of lower stratospheric aerosol from a multiyear lidar data set. J. Geophys. Res., 100(D2), 1995, 3139-3148.
D. M. Tratt and R. T. Menzies: Evolution of the Pinatubo volcanic aerosol column above Pasadena, California observed with a mid-infrared backscatter lidar. Geophys. Res. Lett., 22(7), 1995, 807-810.