88th Annual Meeting (20-24 January 2008)

Wednesday, 23 January 2008
CFLOS and cloud statistics from satellite and their impact on future space-based Doppler Wind Lidar development
Exhibit Hall B (Ernest N. Morial Convention Center)
George D. Emmitt, Simpson Weather Associates, Charlottesville, VA; and S. Greco, D. M. Winker, and Y. Hu
Poster PDF (162.7 kB)
Before the launch of ICESat (GLAS) and CALIPSO, the Doppler lidar community relied upon airborne missions to conceptualize the global distribution of backscatter. In addition, cloud statistics, with a space-based lidar perspective, had been limited to < 40 hours of LITE (Lidar In-space Technology Experiment) data obtained during a 14 day shuttle mission in 1994. Most currently available cloud statistics are based upon data from imagers or passive sounders (for example, ISCCP). Global cloud coverage varies from ~ 65% to >80% depending upon the threshold of optical depth chosen for defining a cloud and the “pixel” size. However, these satellite based cloud coverage statistics are not appropriate for laser beams with diameters of a few meters. The general conclusions of the limited LITE data analyses of cloud porosity for lasers were that the532nm beam provided a ground return more often (~60 - 65%) than the current cloud climatologies based upon passive imagers suggested (~30-40%) and that the porosity of the clouds to the LITE beams was on the order of 50%.

More recently, very preliminary analysis of GLAS cloud data have shown that:

1. 70 - 80% of the GLAS lidar samples involved some return from clouds (assumed that “no cloud/no ground returns” intercepted thick layers of optically thin clouds)

2. 75 - 80% of the GLAS lidar samples detected the earth's surface (adjusted for smooth water returns)

3. When clouds were present, 25 – 40% of the time at least two layers were detected.

Following the work we have done with GLAS/ICESat, we are developing a set of cloud free line-of-sight (CFLOS) and cloud penetration statistics and atmospheric optical properties for space-based Doppler Wind Lidar (DWL) design using both LITE and CALIPSO data, and also using a Doppler Lidar Simulation Model (DLSM) to conduct basic trade studies that relate directly to DWL lidar design and scanning options. The primary LOS statistics are: probability of CFLOS penetrations to specific levels (1 km resolution) in the atmosphere; probability of multiple level interceptions of clouds of low to modest optical depths (< .5); and probabilities of contiguous CFLOSs for various durations of beam stares and shot integration.

The impacts that these cloud statistics have on a future space-based Doppler Wind Lidar will be discussed and simulated coverage illustrated.

Supplementary URL: