Nofel Lagrosas

Determination of aerosol extinction coefficient and mass extinction efficiency by DOAS with a flashlight source

With the method of differential optical absorption spectroscopy (DOAS), average concentrations of aerosol particles along light path were measured with a flashlight source in Chiba area during the period of one month. The optical thickness at 550 nm is compared with the concentration of ground-measured suspended particulate matter (SPM). Good correlations are found between the DOAS and SPM data, leading to the determination of the aerosol mass extinction efficiency (MEE) to be possible in the lower troposphere. The average MEE value is about 7.6m2.g−1 and the parameter exhibits a good correlation with the particle size as determined from the wavelength dependence of the DOAS signal intensity.

High-efficiency aerosol scatterometer that uses an integrating sphere for the calibration of multiwavelength lidar data

For the purpose of calibrating multiwavelength lidar data, we developed a scatterometer to measure the aerosol scattering coefficient at the ground level. The system is based on an integrating sphere, cw lasers (532 and 633 nm), and a controlled flow of the ambient air, including aerosol particles. The simulation study and experimental results indicate that the detection efficiency of this instrument is approximately 10%-40% better than that of an integrating nephelometer, because of the wider acceptance angle of the scattered light. The scattering coefficients measured at the two wavelengths, as well as the resulting value of the angstrom exponent, show good correlation with the results simultaneously measured with an integrating nephelometer and an optical particle counter.

Determination of vertical distributions of aerosol optical parameters by use of multiwavelength lidar data

We propose a lookup table method to derive vertical distributions of aerosol optical parameters in the troposphere from multiwavelength observations using a Mie-scattering lidar. The method is characterized by the capability of treating generalized aerosol size distributions, as well as by rapid convergence of the iteration procedure. The methodology and numerical simulation are described.

Automatic correction of optical alignment deterioration of a continuously operated Mie lidar

Alignment of the laser beam and telescope axes is crucial to the acquisition of high quality lidar data. For a continuously operated Mie lidar, a routine alignment correction is needed to ensure that its data are not influenced by the misalignment and thus truly represent the aerosol and cloud behavior. This paper describes the operation of such a lidar system with automatic correction of optical alignment.

Simultaneous observation of temporal and spatial distribution of atmospheric aerosol by means of slant-path and plan position indicator lidars

The influence of aerosols to the atmosphere has been discussed in the context of the Earth radiation budget and global climate change. Therefore, precise monitoring of aerosol parameters is important for better understanding of their real characteristics and impacts on the environment. In this study, we report on a novel method of concurrent measurements of aerosol near the surface level by means of slant-path (SP) and plan position indicator (PPI) lidars. The SP lidar utilizes a diode-laser-pumped Nd:YAG laser operating at 532 nm, while the PPI is based on a Nd:YLF laser at 349 nm. The PPI system including the laser transmitter and telescope section is rotated over 360° for covering all the horizontal directions with the maximum observation range up to around 3 km. At the same time, the SP lidar is employed for monitoring the near surface region that cannot be covered by vertical observation lidars. Furthermore, the backscattered signals recorded by both PPI and SP lidars are analyzed using the Fernald method to retrieve aerosol extinction coefficient by employing lidar ratios for 349 and 532 nm. These values of lidar ratio are estimated by adjusting and fitting parameters in the Mie scattering calculation (mode radius, variance, and both real and imaginary parts of refractive index) to real data from ground-based sampling instruments, namely, the scattering coefficient, absorption coefficient, and size distribution observed with an integrating nephelometer, an aethalometer, and an optical particle counter, respectively. Real-time values of the extinction coefficient inside the atmospheric boundary-layer are derived as the summation of scattering and absorption coefficients. The results are then compared with those from a vertical lidar, operated by the National Institute of Environmental Studies (NIES) on the campus of Chiba University. We discuss the observed features of aerosol characteristics that vary both temporally and spatially.