The purpose of this study is to present an extension to the technique of water vapor mapping, which was published in a recent paper [Hanssen et al.(1999)]. In that paper it is shown how observations from synthetic aperture radar (SAR) interferometry can be used to extract information on the moisture distribution in the boundary layer. Here we demonstrate how the same radar observations can also be used for wind field measurements, which enables an integrated analysis of wind and moisture parameters from a single sensor. Since mesoscale surface winds modulate fluxes of momentum, heat, and moisture--the driving forces of atmospheric circulation--there is close correpondence between the wind field and the transport and distribution of moisture. Examples include, e.g., cumulus convection and atmospheric dynamics near fronts. Improved understanding of both spatial and temporal behavior of air masses is important for parameterizations in weather forecasting and climate models.
Current observation methods are often limited in the spatial resolution they provide. Moreover, radiometric water vapor observations from contemporary meteorological satellites usually originate from atmospheric layers above 3 km, due to the strong absorption by water vapor [Weldon and Holmes(1991)]. This often restricts quantitative interpretation to upper tropospheric moisture distribution [Schmetz et al.(1995)]. Generally, basic meteorological parameters such as wind velocity and water vapor distribution are not measured on km-scales (see, e.g., Stoffelen [1998] for wind measurents and Susskind et al. [1984] for temperature and humidity information). A related problem is that wind and moisture observations are usually acquired by different sensors, that don't necessarily coincide in time. For the analysis of causal connections between both types of parameters on scales between 100 m and 10 km, temporal coincidence is imperative due to their spatial and temporal variability.
In this paper we elaborate on two case studies, previously presented in Hanssen et al. [1999], where we exploit both the radar backscatter intensity and phase information. This approach provides a more thorough examination of previous findings, which were based on phase information only. Using two pairs of interferometric SAR observations the moisture distribution over land areas is retrieved from the interferometric phase, whereas wind information is retrieved from the backscattered radar energy over water areas. The case studies constitute a comprehensive quantitative examination of vortices associated with a system of boundary layer rolls and with a rain band in relation to a cold front.