Ionospheric effects on synthetic aperture radar at 100 MHz to 2 GHz

Abstract

Abstract. Recently, there has been increasing interest in the use of spaceborne synthetic aperture radar (SAR) for measuring forest biomass. However, it is noted that conventional SAR using Cband or higher frequencies cannot penetrate into foliage, and therefore the biomass measurements require longer wavelengths, typically P-band (500 MHz). It is also known that the ionosphere is highly dispersive, causing group delay and broadening of pulses. The variance of the refractive index fluctuations due to turbulence is approximately proportional to f '4. In addition, the Faraday rotation due to the geomagnetic field in the ionosphere becomes significant. This paper presents an analysis with numerical examples of the following effects in the frequency range from 100 MHz to 2 GHz in order to show the frequency dependence and the effects of total electron content (TEC) of the ionosphere. First, the ionospheric turbulence can reduce the coherent length below the equivalent aperture size, and the azimuthal resolution becomes greater than D/2, where D is the antenna aperture size. Second, the ionospheric dispersion causes a shift of the imagery due to the group velocity. Third, the dispersion also creates broadening of the pulse. In addition, multiple scattering due to ionospheric turbulence gives rise to pulse broadening. Fourth, we consider the Faraday rotation effect and show that the ellipficity change is negligible, but the orientation angle changes significantly at P-band. Numerical examples are shown using typical ionospheric parameters, turbulence spectrum, and TEC values.

Impacts of ionospheric scintillation on geosynchronous SAR focusing: preliminary experiments and analysis

“…The original dataset was recorded by TerraSAR-X over the Aswan Dam in Egypt. For simplicity, the reconditioned scene is set as about 5 km × 5 km, so the ionospheric scintillation is coherent within the scene [7] and the Spectra Analysis (SPECAN) algorithm is adopted for imaging [1]. Otherwise, for a large scene, signals in different areas of the image will be affected differently by the ionospheric scintillation because of their obviously different propagation paths within the ionosphere.…”

Simulation of ionospheric effects on SAR imaging with noise at P-band

“…This perturbation will be particularly severe at P-band and will distort the SAR image along the azimuthal direction. If the ionosphere fluctuations are considered, the azimuthal generalized ambiguity function is given by [7] Range in meters is the propagation complex phase fluctuation due to the ionosphere. In order to solve the problem of fluctuation through the ionosphere, we use a twoparameter spectrum model to generate the random horizontal profile of the electron density [6].…”

Baseline Estimation in Distributed Spaceborne Interferometry SAR Systems

“…Since the effect of ionosphere can be compensated by using experiential radio propagation models [13] A…”