Aperture synthesis radar imaging for upper atmospheric research

Abstract

Radars used for upper-atmospheric applications can be engineered to measure the Doppler spectra of their targets adequately for most intents and purposes, the spectral resolution being limited only by the observing time and the constraints of stationarity. Likewise, they can measure the range to their targets adequately for most intents and purposes, range resolution being limited by system bandwidth, the power budget, and the constraints of stationarity. Problems arise for “overspread” targets, where range and frequency aliasing cannot simultaneously be avoided using pulse-to-pulse methodologies, and more complicated pulse-to-lag or aperiodic pulsing methods are required (see for example (Farley, 1972; Huuskonen et al., 1996; Lehtinen, 1986; Sulzer, 1986; Uppala, 1993)). Important examples of this situation include incoherent scatter experiments (Farley, 1969), observations of meteor head echoes (Chau & Woodman, 2004), and observations of plasma density irregularities present in certain rapid flows, as are found in the equatorial ionosphere during so-called “equatorial spread F” (Woodman, 2009; Woodman & La Hoz, 1976).