Neutral thermospheric dynamics observed with two scanning Doppler imagers: 1. Monostatic and bistatic winds

Doppler‐shift measurements of the thermospheric 630.0 nm emission recorded by two spatially separated imaging Fabry‐Perot spectrometers in Alaska have been combined to infer F region horizontal wind vectors at approximately 75 locations across their overlapping fields‐of‐view. These “bistatic” horizontal wind estimates rely only on an assumption regarding the local vertical wind (and assume a common observing volume), and thus represent a more direct measurement of the wind than do the monostatic (single‐station) vector wind fields routinely inferred by these instruments. Here we present comparisons between both the independently derived monostatic wind fields from each instrument and the bistatic wind estimates inferred in their common observing volumes. Data are presented from observations on three nights during 2010. Two principal findings have emerged from this study. First, the monostatic technique was found to be capable of estimating the actual large‐scale wind field reliably under a large range of geophysical conditions, and is well suited to applications requiring only a large‐scale, ‘big picture’ approximation of the wind flow. Secondly, the bistatic (or tristatic) technique is essential for applications requiring detailed knowledge of the small‐scale behavior of the wind, as for example is required when searching for gravity waves.