Atmospheric Aerosol monitoring

BCO  – VERITAS  LIDAR PROJECT

LIDAR (light detection and ranging) is a technique which involves the firing of short laser pulses to remotely measure properties of scattered light. This device was calibrated for use at BCO during 2011 and it has been deployed at the Fred Lawrence Whipple Observatory in Arizona USA for use by the VERITAS group.

The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is a collection of four telescopes used to detect astrophysical sources of Very High Energy (VHE) gamma rays. VERITAS is located at the Fred Lawrence Whipple Observatory south of Tucson, Arizona, U.S.A., and is operated by a collaboration of more than 100 scientists from 20 different institutions in the United States, Ireland, England and Canada

LIVE LIDAR data. Updated every 10 minutes with information on clouds and aerosols above the Whipple Observatory in Arizona.

View the live feed here

What is LIDAR?

It is mainly used to determine the distance to a target from the time taken between the transmission of a pulse and the detection of the reflected pulse.

Its operation is similar to RADAR however LIDAR uses shorter wavelengths (ultraviolet to infrared) which permits the detection of smaller particles than RADAR.

The specific application is the monitoring of the clarity of the atmosphere and involves aiming the LIDAR in a vertical direction with the laser pulses being partially reflected from backscattering by aerosols in the atmosphere. The intensity of the backscattered light as a function of time gives information on the height distribution and concentrations of the aerosols. High level aerosols such as clouds and volcanic ash are detectable as well as low altitude aerosols (dust) in the boundary layer up to 2 km above the surrounding terrain.

This dust is propagated up into this layer by a combination of wind and convection currents arising from solar heating of the ground during the daytime.

All of these aerosols absorb and scatter light which can affect the quality of astronomy observations. Measurements from the LIDAR can be used to compensate for variations in astronomical data arising from changes in atmospheric conditions. The particular device being used is a Vaisala CL51 LIDAR which operates at an infrared at a wavelength of 910 nm. It provides a backscattering profile range of 0 to 15 km with a reporting resolution of 10 m.  The device fires 110 ns laser pulses  at a repetition rate of 6.5 KHz n nAverage power of the laser is 19.5 mW with a beam divergence of ~ 0.02º.

The LIDAR was funded from the Science Foundation Ireland Research Frontiers Programme grant 10-RFP-AST2748