Validation of Lidar Retrieval of Aerosol Extinction During Indoex with an Airborne 180 deg Backscatter Nephelometer
Abstract
LONG-TERM GOALS. LIght Detection And Ranging (LIDAR) can be used to estimate atmospheric optical extinction by aerosol particles along the laser path if the ratio of extinction to 180 backscattering, referred to as the lidar ratio , is known. Lack of accurate knowledge of the lidar ratio is the largest source of uncertainty when trying to invert elastically scattered lidar signals. This translates into an unacceptably large uncertainty in the determination of particle related extinction and visual range by such instruments. We have developed, calibrated and field-tested a new device for direct, high-accuracy measurement of 180 backscattering by particles (Doherty et al., 1999). When run in conjunction with instruments that measure total light extinction coefficient by particles, the 180 backscatter nephelometer allows for insitu determination of the lidar ratio. Our goal is to use this new measurement capability to more realistically constrain the range of lidar ratios employed to invert elastically scattered lidar signals. OBJECTIVES. Our current research efforts are driven by the following three objectives: (1) to make regional surveys of the lidar ratio, exploring the magnitude and variability in the quantity, (2) to assess the adequacy of current parameterizations of the lidar ratio which are based on Mie Theory using assumed or measured particle size distributions, and (3) to perform an objective calibration of the lidar retrievals of 180 backscattering, optical extinction, and the lidar ratio. The variability of lidar ratio is the result of varying chemical and physical properties of the aerosol, coupled with meteorological factors and the sources of the aerosol. The final goal can be accomplished by making coincident measurements with a calibrated Raman lidar, which is independently capable of retrieving all of these values.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 30, 1999
- Accession Number
- ADA636469
Entities
People
- David S. Covert
- Robert J. Charlson
Organizations
- University of Washington