L‐Band Synthetic Aperture Radar Observation of Ionospheric Density Irregularities at Equatorial Plasma Depletion Region

Plasma density irregularities in the equatorial ionosphere are thought to cause the distortions of L‐band Synthetic Aperture Radar (SAR) images, which have been observed in recent years, but the origin of the image distortion has not yet been clearly identified experimentally. We report on the first simultaneous observation of equatorial plasma bubbles (EPBs) by the ALOS‐2/PALSAR‐2 satellite and ground 630‐nm airglow imager in northern Brazil. We observe stripe‐like distortions of SAR signal power that are aligned in the direction of local magnetic field lines. The stripe‐like patterns are observed in the vicinity of airglow depletion. The result shows that the observed L‐band SAR stripes are caused by ionospheric scintillation due to plasma irregularities with the scale size of hundreds of meters associated with EPBs. We show that the SAR scintillation stripes are predominantly found at the location of sharp density gradients in the two‐dimensional form.

Plain Language Summary: Plasma density irregularities in Earth's ionosphere scatter various radio waves. Such density irregularities are known to exist at large‐scale density depletion structures known as equatorial plasma bubbles. Plasma bubbles occur at night‐time in low latitude regions. We observed plasma bubbles by using a radar satellite and ground optical imager. The results demonstrate that two‐dimensional structure of density irregularities of plasma bubble can be extracted when the density irregularities imprint stripe‐like patterns on the radar image. This study suggests that the radar image can be a useful tool to observe Earth's ionosphere.

Key Points:

We present the first simultaneous observation of L‐band Synthetic Aperture Radar (SAR) scintillation stripes and 630‐nm airglow depletion in northern Brazil.

The results show that plasma density irregularities in equatorial plasma bubbles are the source of observed SAR scintillation.

SAR data show the occurrence of scintillation stripes and plasma density gradients near airglow depletion region.