A CSIR principal researcher, Dr Sivakumar Venkataraman, and the head of the department of physics at the Addis Ababa University in Ethiopia, Dr Gizaw Mengistu, have teamed up in an African Laser Centre project to investigate the structure and dynamics of the atmosphere using lidar (light detection and ranging – similar to radar). “As part of our work we are attempting to study and understand global climate change and global warming, currently high on the international agenda,” says Venkataraman. “The important parts of the atmosphere that contribute to global climate change and global warming are water vapour and ozone. Regular monitoring of these is important to gain a better understanding of these phenomena.”
The collaboration has been ongoing since 2007 and has progressed significantly since the project’s inception: a mobile lidar system has been developed by the CSIR and initial results conclude that the system is capable of providing aerosol/cloud backscatter measurements for the height region from ground to 40 km with a 10 m vertical height resolution. The complete lidar system is custom-fitted into a van and hydraulic stabiliser feet have been added to the vehicle suspension to ensure stability during measurements.
“In technical terms,” Venkataraman says, “an Nd:YAG, which is a commonly used laser source for lidar transmission, is presently employed at second harmonic (also called frequency doubling) of 1064 nm. The receiver system employs a Newtonian telescope configuration with a 16 inch primary mirror. A multimode optical fibre is used to couple the received backscatter optical signal from the telescope to the photo multiplier tube (PMT). The data acquisition is performed by a transient recorder that communicates with a host computer for storage and offline processing of data.”
The first lidar measurements of cloud heights in the troposphere were taken in 1963. Since these pioneering attempts, laser remote sensing of the atmosphere has come a long way. The discovery of different laser sources, improvements in detector technology, data collection and analysis techniques, has rendered this technique a highly efficient tool for monitoring the atmosphere. Measurements can be made within a short time scale – a few seconds to a couple of minutes – and the results obtained can accurately reflect the state of the atmosphere during the time of measurement.
In 2009, Venkataraman and Mengistu will attempt field campaign measurements in and around South Africa to provide qualitative information on pollution levels. The duo also plans to conduct novel measurements by employing high/low-repetition lasers.
As part of their efforts to also develop human capital via this initiative, lidar demonstrations will take place at African – including South African – higher educational institutions. The project has also seen the participation and training of PhD and Master’s students, and collaboration with African and French scientists.
Mengistu says, “Our investigations on water-vapour concentration will contribute to the local ecological effects such as regional drought. The ozone studies will complement water vapour measurements and provide a more complete picture on the state of the atmosphere and its effects on global climate change. Therefore, our secondary aim is to upgrade the lidar at a later stage for studying the troposphere ozone concentrations up to 18 km.” Any increase in the troposphere ozone measurements is partly attributed to the rise in temperature and thus contributes to global warming. “Therefore, by investigating these trace molecules over South Africa and the African continent, our work will contribute to studies on global climate change and global warming.”
For more information contact Dr Sivakumar Venkataraman, [email protected]
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