Lidar Measurements of Aerosol Scattering in the Troposphere and Stratosphere
Document ID: 5
Philbrick, C. Russell
Lysak, Jr., Daniel B.
Rau, Yi -Chung
IEEE Proc. Combined Optical-Microwave Earth and Atmosphere
doi: 10.1109/COMEAS.1993.700165
Abstract
A two-color Rayleigh/Raman lidar has been developed to study the properties of the middle and lower atmosphere. The LAMP(Lidar Atmospheric Measurement Program) lidar profiler was placed in service at Penn State University during the summer of 1991. The LAMP lidar uses two wavelengths, 532 and 355 nm, in the transmitted beam and up to eight detectors in the receiver. The instrument is arranged in monostatic configuration, which permits useful measurements in the near field, as well as in the far field. The detector system uses a mechanical shutter to block the high intensity low altitude signal from the high altitude detectors until the beam has reached an altitude of 20 km. The Nd:YAG laser includes a doubling crystal and a mixing crystal to produce a 532 and a 355 nm beam. The low altitude backscatter signals of the visible and ultraviolet beams are detected as analog signals and digitized at 10 MSps to provide 15 meter resolution from the surface to 25 km. The high altitude signals, obtained by photon counting techniques, are separated into 500 nanosecond range bins to provide 75 meter resolution from 20 to 80 km. The detector also contains two first Stokes vibration Raman channels to measure the N2 signal at 607 nm and H2O signal at 600 nm. Measurements of the rotational Raman backscatter provides the possibility to obtain temperature profiles in the presence of clouds and in the boundary layer.
The results reveal the continuous presence of a relatively small aerosol particles through the troposphere. These particle sizes are compatible to the wavelength of the light and exhibit a signal, in the vicinity of 5 km. which is typically greater than the molecular backscatter by a factor of 2 at the 532 nm wavelength and by a factor of 10 at the 355 nm wavelength. The small aerosol component of the tropospheric backscatter was found to be relatively uniform as a function of latitude over the ocean, from Artic (70°N) to Antartic (65°S). In the presence of clouds, the variation in the background small aerosol was remarkably small. The cloud presence does not significantly change the slope of magnitude of the small aerosol component near the cloud layer except for the expected attenuation by the cloud. The magnitude of the of the ultraviolet extinction due to small aerosol component is quite significant. The influence of turbidity due to small aerosol scattering has been investigated to prepare these results for a study of the turbidity contribute to the radiative transfer in the atmosphere.
Notes
“Lidar Measurements of Aerosol Scattering in the Troposphere and Stratosphere,” C. R. Philbrick, D. B. Lysak and Y.-C. Rau, Proceedings of the IEEE Topical Symposium on Combined Optical-Microwave Earth and Atmosphere Sensing, 107-110, 1993.
Keywords: lidar, Raman lidar, lidar atmospheric measurement program (LAMP), R. V. Polarstern