PBL water vapour spatial statistics from VSWIR reflectance

Abstract:

In many meteorological scenarios the horizontal spatial variability of the total column water vapour (TCWV) can be related to the turbulent mixing within the planetary boundary layer (PBL). This presentation will show our efforts to derive water vapour spatial variance and structure functions at very high resolution using reflected solar spectra. Airborne shortwave (SW) reflectance spectra have been successfully inverted to simultaneously retrieve surface properties and atmospheric TCWV. While no vertical structure is retrieved, the horizontal TCWV variability is dominated by the PBL and this retrieval technique offers wide swaths and excellent nominal horizontal resolution: metres if airborne, tens of metres if spaceborne. However, in reality the light passes diagonally through the atmosphere and encounters vapour across a wider horizontal range. This presentation reports on an LES OSSE in which SW column water vapour retrievals are used to estimate horizontal spatial statistics of PBL water vapour accounting for the light’s path. Spatial variance and the second order structure function, which are related to PBL dynamics, are obtained. We explore measurement architectures or targeting criteria that could reduce biases introduced by challenging solar or view geometries.