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 S 4 and vertically integrated strength of turbulence C k L, 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 S 4 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.

Monitoring of Ionospheric Scintillation Phenomena Using Synthetic Aperture Radar (Sar)

“…The average S4 measured at Tirunelveli station is 0.21 on March 23, 2015 (Mohanty, et al 2018). This has been computed taking into account all the satellites observed at the station within a three-hour time window (17:30 to 20:30 UT) and satisfied a criterion.…”

“…The same applies to satellites to the east of the SAR track post 1900 UT. Details of measurement of the plasma drift and the selection of GPS satellites to be included in the study are explained and given in (Mohanty, et al 2018). The slight variation in S4 measured from GPS and that estimated from SAR pairs is due to the difference in position of the ionospheric pierce points of the satellites and SAR.…”

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

“…The deformation of SAR images is characterized by stripe‐like structures aligned with the local geomagnetic fields, which can stretch over 1,000 km. Although a recent report shows that SAR and GPS scintillation were observed on the same night in the Indian sector (Mohanty et al., 2018), the origin of SAR scintillation and its possible relation to EPBs are not yet observationally evident due to the lack of simultaneous observation of ionospheric density depletions.…”

“…observed on the same night in the Indian sector (Mohanty et al, 2018), the origin of SAR scintillation and its possible relation to EPBs are not yet observationally evident due to the lack of simultaneous observation of ionospheric density depletions.…”

Detection and Characterization of Ionospheric Activity at High Latitude from SAR Measurements

“…This effect is used to estimate TEC and to produce TEC map from SAR acquisitions [4]. Furthermore, the ionospheric scintillation parameter S 4 is estimated using two SAR acquisitions on two different dates [5] in India. The estimated S 4 is compared with the one measured by GNSS receivers positioned along the orbit of the space-borne SAR sensor and the results are qualitatively consistent.…”