SOS 1999 Ground-based Lidar Scanning Strategies
The following information mainly applies to the Doppler lidar. Coordination with the ground-based ozone lidar is mentioned when appropriate.
Survey Sequence (executed every 45 min)
Constant elevation scans (covering 360° in azimuth): 0° (if useful), 1°, 2°, 3°, 5°, 10°, 15°, and 30° above the horizon.
Constant azimuth scans (horizon-to-horizon): beginning at 0°, 20°, 40°, 60°, 80°, 100°, 120°, 140°, and 160° azimuth.
To fill out the rest of the 45-min time period, scans will be chosen according to the time of day, current meteorological conditions, and scientific objectives.
Daytime Convective Boundary Layer (CBL)
Scientific Objectives: vertical mixing intensity in the CBL, evening collapse of CBL, turbulent kinetic energy (TKE)/momentum flux calculations within the CBL, cloud venting
- Vertically pointing scans that measure w (vertical motion) for ~30 min. Coordinate with ozone lidar.
- TKE, momentum flux scans for ~30 min (elevation angles of 35.5° and 50.8°).
- If moderate daytime winds - especially southwesterly winds (urban outflow):
- Azimuth sector scans (Δ azimuth = 30° - 50°) into the wind (SW) or downwind (NE) to document variability in the wind and aerosol fields. Repeat for 10-15 min or more. Use lowest elevation angle that isn't obstructed. Coordinate with ozone lidar pointing horizontally upwind or downwind.
- Can intersperse some shallow vertical scans (spanning < 30° elevation from surface) pointing upwind or downwind for 2-5 min. If time permits, execute cross-wind vertical scans.
- Ozone lidar - emphasize vertically pointing scans.
Evening Transition, Nighttime
Scientific Objectives: development of low level jet (LLJ) and inertial oscillation (IO), buildup of stable boundary layer (SBL)*, 'leakage', and mixing height
Cold air layer buildup and structure of vertical and horizontal eddies, waves, and layers: Repeated shallow upwind or downwind vertical scans (spanning < 30° elevation from surface) and
Repeated shallow upwind or downwind azimuth sector scans (lowest elevation angle without obstruction).
For both horizontal and vertical scans, can increment small changes in angle and obtain small volume of measurements.
If winds are strong and mixing down to the surface (i.e., there is an absence of a cold air buildup), then execute TKE/momentum flux scans between survey scans.
If documenting the LLJ, use deeper along-wind vertical scans.
Ozone lidar - emphasize vertical scanning (coordinate with Doppler lidar).
* Highest priority objective
Scientific Objectives: dissolution of nighttime boundary layer (NBL), fumigation of layers
Same strategy as nighttime transition.