A Variational Method for Real-Time Retrieval of Three-Dimensional Wind Field from Multiple-Doppler Bistatic Radar Network Data

A variational method for the retrieval of the 3D wind field from bistatic multiple-Doppler radar network data is developed, and its performance is evaluated. This bistatic network consists of one S-band weather radar and two passive low-gain receivers at remote sites. To allow for measurement error, the method uses the Doppler velocities of the three receivers as weak constraints and uses the continuity equation as a strong constraint in a cost function in which the two horizontal wind components are the control variables. Improvements are brought to the classical upward integration of the continuity equation, using a weighted combination of upward and downward integrations and its adjoint. A unique characteristic of a bistatic network is that all Doppler velocity measurements from individual resolution volumes are collected simultaneously, which minimizes the errors on the vertical wind component arising from the local evolution of the airflow. However, the time required to sample a complete weather volume with a Doppler radar (typically 5 min) represents another source of error that must be accounted for. Consequently, linear time interpolation of the measurements to a single reference time is used. Finally, evaluation of the volume scanning strategy for aviation weather services shows that two retrieval modes can be processed in parallel, using the McGill University radar scanning strategy: a “fast” mode that provides the 3D wind field below 3-km height every 2.5 min and a “standard” mode that provides the 3D wind field for the full volume every 5 min.