Abstract
Retrieval of ionospheric parameters from spaceborne synthetic aperture radar (SAR) and SAR interferometry (InSAR) observations has been developed in recent years due to its high spatial resolution. However, current studies are centered on the one-dimensional or two-dimensional ionospheric parameters, and there is a lack of retrieving three-dimensional ionospheric electron density. Based on this background, this study proposes an efficient method to map high-spatial-resolution three-dimensional electron density by combing of the full-polarimetric SAR images and international reference ionosphere (IRI) model. For a performance test of the proposed method, two L-band Advanced Land Observation Satellite (ALOS) Phase Array L-band SAR (PALSAR) full-polarimetric SAR images over Alaska regions are processed. The high-spatial-resolution ionospheric parameters, including vertical total electronic content (VTEC) and three-dimensional ionospheric electron density, are reconstructed over the study area. When comparing with the electron density derived from Poker Flat Incoherent Scatter Radar (PFISR) system, it is found that the IRI-derived electron density is obviously improved, where the standard deviations of differences between PFISR and IRI decrease respectively by about 2 times and 1.5 times compared to those before the correction, demonstrating the reliability of the proposed method. This study can help us better understand the characteristics of ionospheric variation in space.
Highlights
The ionosphere, extending from ∼60 to 1,000 km above the earth’s surface, is an important part of the solar–terrestrial space environment (Davies and Smith, 2002; Hunsucker and Hargreaves, 2007)
There are the difficulties in obtaining the high-spatial-resolution vertical TEC (VTEC) and three-dimensional electron density for the current methods and models
The following conclusions are summarized: (1) The VTEC distribution with high spatial resolution is successfully mapped from the full-polarimetric synthetic aperture radar (SAR) data
Summary
The ionosphere, extending from ∼60 to 1,000 km above the earth’s surface, is an important part of the solar–terrestrial space environment (Davies and Smith, 2002; Hunsucker and Hargreaves, 2007). When SAR signals travel through the ionosphere, they interact with the electrons and the magnetic field with the result that additional time delay, phase advance, and polarization changes are produced (Zhu et al, 2016) By means of this phenomenon, the ionospheric parameters can be estimated from SAR and SAR interferometry (InSAR) observations (Wang et al, 2017). This method exploited the dispersive nature of radar signals in estimating the ionospheric signals Based on this method, Wang et al (2014) proposed a triband path delay technique to retrieve the TEC and evaluated it through simulation, and Kim and Papathanassiou (2014) investigated a set of ionospheric parameters by exploring range and azimuth subbands in SAR imagery. Based on this method, Wang et al (2014) proposed a triband path delay technique to retrieve the TEC and evaluated it through simulation, and Kim and Papathanassiou (2014) investigated a set of ionospheric parameters by exploring range and azimuth subbands in SAR imagery. (Maeda et al, 2016) imaged the kilometer-scale fine structures of midlatitude sporadic E plasma patches by an interferogram from ALOS data over southwestern Japan, revealing a detailed horizontal structure of sporadic E. Mannix et al (2017) and Belcher et al (2017) calculated the ionospheric scintillation parameters through analyzing SAR phase variations of the corner reflectors and showed the consistent results with the GNSS-derived parameters, demonstrating the feasibility of ionospheric parameters derived from SAR images
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