AIRBORNE CO2 COHERENT LIDAR MEASUREMENTS OF CLOUD BACKSCATTER AND OPACITY OVER THE OCEAN SURFACE

The use of an airborne CO2 lidar to obtain cloud backscatter and extin ction data at a thermal infrared wavelength is described. The extincti on in this spectral region is proportional to the cloud liquid water c ontent. The use of coherent detection results in high sensitivity and narrow field of view, the latter property greatly reducing multiple-sc attering effects. Backscatter measurements in absolute units are obtai ned through a hard target calibration methodology. For clouds of low t o moderate optical thickness at the lidar wavelength, both geometric t hickness and optical thickness can be measured. The sea surface reflec tance signal is used to obtain estimates of the cloud optical thicknes s. The utility of this technique results from studies that indicate th at the spatial scale of variability of the sea surface reflectance is generally large compared with that of cloud optical thickness. Selecte d results are presented from data taken during flights over the Pacifi c Ocean.