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.