Ionospheric Scintillation Observation Using Space-Borne Synthetic Aperture Radar Data

Abstract

Networks of ground-based global navigation satellite system (GNSS) receivers have been widely used to monitor scintillation caused by irregularities in the disturbed ionosphere. Due to the relative sparseness of such networks, however, scintillation measurements are lacking in many regions of the globe, and even in well-instrumented geographic areas, the spacing between receivers is often too large to study the systematic spatial changes in scintillation characteristics, for example, across the equatorial anomaly region. This paper discusses the potential of studying ionospheric scintillations using low-frequency synthetic aperture radar (SAR). It compares standard metrics of scintillation including the amplitude scintillation index S4 and vertically integrated strength of turbulence CkL, from GNSS and SAR, on two different dates with varying ionospheric conditions. For this study, polarimetric L-band SAR images acquired from the Phased Array-type L-band Synthetic Aperture Radar sensor onboard the Advanced Land Observational Satellite-2 have been used. A number of GNSS satellites also observed the particular scintillation event that was encountered by SAR on the night of 23 March 2015 over the southern and mid-central India. The S4 index derived from SAR are computed using previously published techniques in terms of radar backscatter (σ°) enhancement and the image contrast. The results show a favorable correlation with the GNSS observations. Along with accurate information about satellite geometry and operating frequency, few spectral properties of ionospheric irregularities, such as spectral index, anisotropy, and outer scale, have been assumed from historically available low-latitude scintillation observations to calculate the turbulence strength parameter. The results are well corroborated by measurements from four GNSS stations in India, thus demonstrating the utility of the SAR measurements in augmenting and complementing the ionospheric scintillation diagnostics available from GNSS.