Fluorescence measurement of volcanic ash applying multispectral lidar in Buenos Aires

NOBUO SUGIMOTO; JACOBO SALVADOR; EZEQUIEL EDUARDO PAWELKO; EDUARDO J. QUEL

Santos

Workshop; IX WLMLA (Workshop on Lidar Measurements in Latin America); 2016

Instituto de Pesquisas Energéticas y Nucleares (IPEN Brasil)

On April 22, 2015, Calbuco volcano located in southern Chile (41° 19' S and 72° 37' W) erupted and a large amount of volcanic ash was transported and dispersed by the atmosphere over South America. At that moment, at CEILAP (Laser Research and Applications Center) (34° 33' S and 58° 30' W), Buenos Aires, Argentina, there were an experimental fluorescence and Raman multispectral lidar and passive remote sensing instruments such as a sunphotometer (linked to AERONET/NASA) and ultraviolet and visible broadband radiometers, operating and monitoring the atmosphere. In this case and probably for the first time, it was possible to measure a fluorescence spectrum of volcanic ash with high vertical, temporal and spectral resolution applying the multispectral lidar tecnhique. This instrument works with a pulsed Nd:YAG laser (1064 @ 650 mJ, 532 and 355 nm) at 10 Hz repetition rate and two reception subsystems. One of them consist of a 50 cm diameter Newtonian telescope in coaxial arrangement with the laser beam. It is connected to a lidar spectrometer in order to process the inelastic return signals from aerosols and molecules excited by 355 nm laser wavelength. The lidar spectrometer consists of a Crossed Czerny-Turner spectrometer, a 32 channels hybrid photomultiplier and a photocounting detection device, which works at 15 m spatial resolution and 4.5 nm spectral resolution. The second receptor is a 20 cm diameter Newtonian telescope in biaxial setup, which isused to collect the 532 nm orthogonal polarization backscatter. The aim of this work is to present new results to improve the study and monitoring of volcanic ash in the framework of LALINET (Latin America Lidar Network) and SAVER-Net/SATREPS (South American Environment Risk Network) networks. This paper shows the lidar spectra of a volcanic ash plume monitored between 3.5 and 5 km height on April 25, 2015. The atmospheric Raman backscatter of Oxygen, Nitrogen and Water Vapor and the fluorescence response of ashes are presented in a same spectral measurement. The result of the lidar is analyzed together with optical and x-ray spectrometry of volcanic ash collected 100 km far from the volcano, in which chemical species and the fluorescence spectrum are identified. Finally, the effect of contamination by fluorescence on Raman lidar measurements of volcanic ash is discussed.