Extended overdetermined dual-doppler formalism in synthesizing airborne Doppler radar data

Abstract

During the intensive observing period of the field phase of the Coupled Ocean-Atmosphere Response Experiment (COARE) of the Topical Oceans and Global Atmosphere (TOGA) program, airborne Doppler radars capable of fore-aft scanning (dual-Doppler analog) were involved in aircraft missions in which highly coordinated and parallel tracks were flown (quad-Doppler analog). Pairs of observations from each radar can be used to infer the wind components through an iterative dual-equation solution, while combining them allows a direct determination. Errors from these two analysis methods are discussed, in particular those induced from geometrical considerations. Due to these geometrical limitations, neither the dual-Doppler nor the quad-Doppler approach can take advantage of the whole volume sampling. To overcome the limitations and to increase considerabty the synthesis domain, the overdetermined dual-Doppler (ODD) technique is proposed in an extended version (EODD). EODD includes solutions to these problems as well as means to mitigate the inevitable contribution of errors in estimating the vertical velocity, previously described in early studies. The EODD technique is applied to data collected in a squall line that occurred near Guadalcanal Island on 22 February 1993, from Doppler radars aboard the two NOAA WP-3D aircraft. Similar airflow structures, consistent with those from previous studies, are obtained from application of the EODD method to dual-Doppler and quad-Doppler observations, indicative of the validity of using the proposed method to solve either dual- or quad-Doppler data configurations.