Hiroatsu Sato

Detection and Estimation of Equatorial Spread F Scintillations Using Synthetic Aperture Radar

A significant amount of the data acquired by sun-synchronous space-borne low-frequency synthetic aperture radars (SARs) through the postsunset equatorial sector are distorted by the ionospheric scintillations due to the presence of plasma irregularities and their zonal and vertical drift. In the focused SAR images, the distortions due to the postsunset equatorial ionospheric scintillations appear in the form of amplitude and/or phase “stripe” patterns of high spatial frequency aligned to the projection of the geomagnetic field onto the SAR image plane. In this paper, a methodology to estimate the height and the drift velocity of the scintillations from the “stripe” patterns detected in the SAR images is proposed. The analysis is based on the fact that the zonal and vertical drift of the plasma irregularities are, at the equatorial zone, perpendicular to the geomagnetic field which is almost parallel aligned to the orbit. The methodology takes advantage of the time lapse and change of imaging geometry across azimuth subapertures. The obtained height estimates agree well with the reference measurements and independent estimates reported in the literature, while the drift velocities appear slightly overestimated. This can be attributed to a suboptimum geometry configuration but also to a decoupling of the ambient ionosphere and the plasma irregularities.

Estimation of drift of equatorial ionosphere of post sunset-sector by means of low frequency space-borne SAR

Recent studies indicate the potential of low frequency space-borne SAR sensors to monitor and quantify structure and dynamics of ionosphere [1-3]. At the post-sunset sector of the equatorial ionosphere, the instability of the electron density often induces plasma bubbles aligned to the geomagnetic field [4], whose effects are seen as distinctive stripe patterns on SAR data [5-6]. At the same time, the free-electrons in this sector of ionosphere drift eastward [7]. This paper explores this effect captured on ALOS and ALOS-2 SAR data to estimate the drift velocity and altitude of the bubbles [8]. Based on the azimuth sub-band of SAR data analysis the height and velocities are estimated, and compared to the measurements from ionosonde. The sensitivity of the estimates is analyzed, and finally a possible observation configuration for further ionospheric study is proposed.