LIDAR DETERMINATION OF HORIZONTAL AND VERTICAL VARIABILITY IN WATER-VAPOR OVER COTTON

A solar-blind lidar system is being developed for remote noninvasive measurement of atmospheric water vapor concentrations in three dimensions and over time. Based on a high-power KrF laser operating at 248 nm, the truck-mounted system has 1.5-m resolution of water vapor concentrations along the beam path from 100 m to 500 m from the truck location. Field tests in 1988 over an incomplete cotton canopy showed that the system (operating in a one-dimensional mode) was capable of detecting small changes in water mixing ratios close to the canopy. Both spatial and temporal trends agreed qualitatively with those measured with conventional point instrumentation. Vertical gradients measured by lidar exhibited a larger range than conventional hygrometric measurements, but the qualitative agreement suggests the potential for lidar to measure small spatial gradients. Further development of the system will allow us to observe the structural detail in turbulent processes over broad areas. Pattern analysis and correlation between time scans will permit the estimation of the movement rates of eddies and their contribution to the overall flux of water vapor. © 1990.