Lidar Measurements

Scanning Lidar System
During the SEAS experiment Scanning lidar measurements were made at Bellows Beach on the South-East side of Oahu (Porter at al., 2002). At this site the scanning lidar was looking straight upwind into the trades. Vertical scans were carried out for one week and the average of these lidar scans illustrated the processes occuring on the windward side of Oahu. The figure below shows this average. Here the logarithm of the aerosol scattering coefficient was averaged. In this way clouds did not dominate the average. Thie figure below shows various processes occuring. The right side of the figure is at the beach and the left side of the figure is upwind of Bellows Beach. Above the trade wind inversion (~1700 m) in the clean free troposphere air.  From ~500 - 1700 m is the cloud layer with the most persistemt clouds at 500m. As these clouds approach Oahu, the blocking effect of the Koolau mountain range caused wind convergence (wind pile up) and the winds start to rise somewhat. This causes cloud growth and enhanced drizzle near the windward coastline (see yellow region in bottom right of the image). Spray from breaking waves on the outer reef causes a local aerosol enhancement but with little vertical extent (for these trade wind conditions).  This study is discussed in Porter et al., 2002 as well as the Meteorology section.

Small Lidar System
The small lidar system is suitable for measurements on a moving platform. An example of this type of measurement is shown below. Here the lidar was pointed upward and mounted on a vehicle and the vehicle was driven under the volcano plume. In this case the road winded under the plume and we passed under the plume three times. Based on these and other measurements we were able to calculate the flux of aerosol and SO2 gas from the volcano plume. Further calculations provided estimates of the half life of the volcanic SO2 gas (Porter et al., 2002). The values on the color bar are the log (base 10) of the aerosol scattering coefficient.