Abstract
Ionospheric effects such as signal path delays, Faraday rotation (FR) and changes in the length of the transmitted pulse depend on frequency. For a linearly frequency-modulated chirp signal, the frequency-dependent time-delays imply a slight change in the chirp rate and a change in the length of the received pulse. The length of the received pulse will be shortened compared with the transmitted pulse for upchirps and broadened for downchirps. An approach is proposed for measuring the ionospheric Total Electron Content (TEC) based on a coded Active Radar Calibrator (ARC) for a spaceborne Synthetic Aperture Radar (SAR). The TEC can be deduced from the phase difference and offset in the range between the downchirp and upchirp retransmitted to the SAR by a coded ARC. The method is not dependent on the phase of the transmitted signal and the range between the SAR and ARC, so the precision of TEC measurement can be improved. Simulations are performed for various band spaceborne SAR sensors of the BIOMASS, TerraSAR-L and HJ1C satellites. The results from the simulation are in accordance with the theoretical analysis and the validity of the method proposed is proved.
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