TEC retrieval from spaceborne SAR data and its applications

Abstract

It is well known that the spaceborne synthetic aperture radar (SAR) at VHF-UHF band can be seriously affected by the ionosphere. Thus, the geophysical information of the ionosphere will be embedded in the low-frequency SAR echoes after they transverse the ionosphere. Correspondingly, the total electron content (TEC), a typical ionospheric information parameter, can be retrieved from the spaceborne SAR data. However, the existing dual-band techniques for TEC retrieval usually do not include consideration of multiple scattering effects caused by turbulent ionosphere, which plays an important role in the total path delay of signal under the strong fluctuation regimes. The result of TEC retrieval is therefore inaccurate and not applicable. Aiming at this issue, first, this paper analyzes the effects of regular background and the irregularity of electron density on SAR at L-band, and the theoretical formulation is given. Then, a triband path delay technique of TEC retrieval based on the SAR data is proposed. By using three path delays corresponding to three specific frequencies within the signal bandwidth, this technique can remove the errors of multiple scattering due to the irregularity, and a high accuracy resolution of TEC value therefore can be obtained. Meanwhile, the sensitivity of this technique is analyzed. Finally, compared with traditional dual-band technique, the numerical simulations show that the correction of SAR imaging based on triband technique is improved significantly. In addition, the resolution of reconstruction imaging using computerized ionospheric tomography performs significantly better based on the triband technique.

Computerized ionospheric tomography based on geosynchronous SAR

“…The initial and true values of electron density are chosen from 100°E–120°E longitude, 10°N–30°N latitude, and 200 km–600 km height. In current spaceborne SAR CIT studies, the grid spacing is around 10–40 km in vertical and around 0.5° in latitude [ Li , ; Li and Li , ; Wang et al ., ]. Correspondingly, the space of ionosphere is divided into 8000 grids, with 0.5° interval in latitude, 1° interval in longitude, and 40 km interval in vertical.…”

“…Wang et al . [] proposed a method to retrieve absolute TEC value by dividing subbands and taking into account the effects of multiple scattering. Meyer et al .…”

Improved TEC retrieval based on spaceborne PolSAR data

“…As a high-resolution active microwave sensor, the spaceborne synthetic aperture radar (SAR) has been widely used in civil and military fields for decades, such as target detection and recognition, resource exploration, biomass classification and retrieval, and topographic surveying [e.g., Pettersson, 2004;Toan et al, 2011;Yang et al, 2015]. Recently, the use of low-frequency spaceborne SAR for measuring ionospheric information, i.e., the total electron content (TEC), has attracted increasing interest [e.g., Meyer et al, 2006;Rosen et al, 2010;Jehle et al, 2010;Meyer, 2011;Pi et al, 2011;Wang et al, 2014;Maeda et al, 2016]. Combining with the high spatial resolution of spaceborne SAR, this new field has the capability to obtain a kilometer-scale TEC distribution, which is difficult to be detected by conventionally used data source [Pi, 2015].…”

“…Given the different signal delay within the bandwidth, the range quadratic phase error (QPE) arises and further degrades the range resolution. TEC values can then be retrieved from the QPE by autofocus algorithm [ Jehle et al ., ; Wang et al ., ]. However, current low‐frequency spaceborne SAR systems, e.g., the Advanced Land Observing Satellite phased array L‐band synthetic aperture radar (PALSAR), have low sensitivity regarding TEC and require a strong point target with high signal‐to‐clutter ratio.…”

Ionospheric Effects on Spaceborne Synthetic Aperture Radar and a New Capability of Imaging the Ionosphere From Space

“…During the last decade, ionospheric effects on spaceborne radar systems have drawn attention of Earth and space scientists [e.g., Ishimaru et al , ; Liu et al , ; Freeman , ; Chapin et al , ; Pi and Chan , ; Freeman et al , ; Meyer and Nicoll , ; Shimada et al , ; Rosen et al , , ; Pi et al , ; Rosen et al , ; Meyer , ; Kim et al , ; Carrano et al , ; Pi et al , ; Chen , ; Kim , ; Kim and Papathanassiou , ; Belcher and Cannon , ; Rogers and Quegan , ; Wang et al , ]. The motivation can be at least partially attributed to development and operation of L band and P band remote sensing radar systems for Earth observations.…”