Modeling the neutral wind velocity based on measurements by scanning Doppler imagers

Recently, a network of three scanning Doppler imagers (SDI) has been installed in the Fennoscandian region, at Abisko in Sweden, and at Aakenus and Kevo in Finland. The combined field-of-view of these instruments covers observation volume of the upcoming tristatic and phased array incoherent scatter radar, EISCAT_3D.  In parallel, a Fabry-Pérot interferometer (FPI) has been relocated from Tromsø to Skibotn, Norway to complement future EISCAT_3D observation of the thermosphere.
Each SDI instrument measures the line-of-sight (LoS) component of the neutral wind velocity and temperature in the upper atmosphere using all-sky observations of auroral emissions. Measurements are derived from the green-line emissions in the E region and the red-line emissions in the F region of the ionosphere. With about 140° field of view, each SDI provides measurements in 115 distinct viewing directions.  Together, the three SDIs form a tristatic configuration with an observation region extending more than 1000 km in both the east–west and north–south directions. However, only a small portion of this region contains overlapping viewing zones from all instruments, which limits the ability to directly retrieve the full three-dimensional neutral wind vector throughout the entire volume.
To address this limitation, here we present a new modeling technique that reconstructs the full neutral wind velocity vector from LoS measurements across observation volume of available SDIs. The method is based on representing the horizontal component of the wind velocity by the spherical elementary basis functions and the vertical component by piecewise constant functions in a gridded observation volume.  We validate our approach using synthetic LoS data generated from WACCM-X thermospheric simulation. We also apply the technique to real LoS measurements from two SDIs and compare the result with an independent FPI measurements. In both comparisons, our method shows a good performance, and when combined with EISCAT_3D measurements, this approach will enable more detailed investigations of ionosphere-thermosphere coupling processes.