Convener:
Jonathan Friedman, NAIC Arecibo Observatory (jonathan@naic.edu)
2004 Thursday 01 July 0330-0530 PM
The lidar technical session was called in order to prompt an open discussion amongst the lidar community and other interested members of the CEDAR community as to what technologies should be brought to bear to resolve the issues presented in the CEDAR lidar community self-assessment report. These issues were both specifically science, as well as how to support upcoming facilities such as AMISR and HIAPER. There were about 30 attendees, with about 10 students. With the stage set by the morning workshop roundtable on science issues for future CEDAR lidars, the presently developed techniques for Doppler-resonance lidar were presented.
Josef Hoeffner of the Leibniz Institute for Atmospheric Physics, Germany, presented the technique behind and evolution of the 15-year old mobile IAP lidar. His talk was entitled: A solid state scanning iron/potassium lidar for precise temperature and vertical wind measurements. He demonstrated how alexandrite lasers can be reliable transmitters for lidar applications. He demonstrated how the IAP alexandrite laser operates reliably over long periods with near-ideal spectral output. Josef showed the system as applied to K and Fe studies of mesospheric temperatures and line-of-sight winds. Finally, he demonstrated that, with optimized present-day technology, there is little statistical difference in temperature and wind measurements made by a solid-state laser-based K and Fe lidar, and those of Na lidars.
C. Y. (Joe) She of Colorado State University, presented a talk entitled: Narrowband sodium lidar transmitter: present performance and future improvements. He began with the history of the CSU Na lidar development and demonstrated its capabilities. Included were examples of the data quality for the full spectrum observing conditions, including day and night for seasons of maximum and minimum Na density. Joe also showed how this lidar, often described as too complex to be broadly applicable, operates continuously and trouble-free over periods of many days; and he posed the question: Can a system too difficult to operate be robust at the same time? He described the fruits of his own efforts to enhance the laser by introducing solid state technology, and he concluded by showing the next stage of upgrades to the "Gold Standard" of resonance lidars, by making it fully solid-state, and thus applicable to mobile and remote platforms.
Dr. Xinzhao Chu of University of Illinois presented the technical aspects of the pre-proposal White Paper she co-authored, in a talk entitled: 3-Frequency Fe/Rayleigh Temperature Lidar for Middle Atmosphere Observations from Research Aircraft and Remote Sites. Xinzhao's talk presented a next-generation Rayleigh-plus-resonance lidar. Improvements to alexandrite lasers in recent years make it an attractive light source not only for the K and Fe lidars, which are already in use, but also a simultaneous Fe resonance and Rayleigh temperature lidar. She pointed out that the simplicity, stability and durability of the system makes it attractive to mobile applications, in particular operation on board the new NCAR Hiaper aircraft.
We then changed gears, and Gary Swenson, University of Illinois, presented "Technologies evolving for Rayleigh lidar." Gary showed developing laser technologies that could be applied to Rayleigh lidar. It is clear that solid-state (diode) laser technologies, coupled with fiber amplifiers, portend a great opportunity. Still, the lack of a broad market for the type of laser appropriate for lidar still make these lasers "custom" products.
Finally, Biff Williams, Colorado State, presented two promising technologies, one to extend the capabilities of existing Na and K lidars to making upper tropospheric and stratospheric wind measurements, and a second to increase receiver apertures in a way that is economical and transportable. In the first technology, a magneto-optical filter can extend the application of resonance lidar, in particular, for K and Na lidars, to make wind, temperature, and aerosol measurements in the troposphere to mid-stratosphere. These would occur simultaneously with the standard mesospheric W/T measurements. The second technology presented was an economical and transportable multiple-mirrored method for building a 3-m class telescope.
It is clear that there is no obvious "winner" for the next generation of resonance lidar transmitter, as Na, Fe, and K lidars each have their advantages and disadvantages. The tradeoffs and technical issues generated a lively discussion and helped us all to be aware of the fact that, though there is no panacea for middle atmospheric lidar, there is a range of choice of technologies that produce comparable results. Given the issues, the community has decided to hold a retreat in late September to finally hash them out and hopefully emerge united with a proposal for the next Doppler resonance lidar.