Geosynchronous SAR: System and Signal Processing by Teng Long Cheng Hu Zegang Ding Xichao Dong Weiming Tian & Tao Zeng

Author:Teng Long, Cheng Hu, Zegang Ding, Xichao Dong, Weiming Tian & Tao Zeng
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

(4.30)

The temporal variant ionosphere will induce the linear, quadratic or higher orders of phase errors, and be sure to result in the image drifts and defocusing. Based on the Taylor expansion, TEC(t a ) can be modelled as the all-order derivatives of the slow time t a . The expanded TEC(t a ) is

(4.31)

where TEC0 is the constant part which is not variant with the time, and k i is the ith temporal derivatives.

In nature, the ionosphere distributes along the altitudes between 50 and 1000 km and it can be represented by a layer at the height of 350 km. When the satellite transmits and receives signals, the line-of-sight will intercept this ionospheric layer and the intercept point is named as the puncture point. When the satellite runs along with its own trajectory, the puncture point also forms a trajectory called the puncture path. This gives an approximation about the description of the trans-ionosphere propagation and the relative movement between GEO SAR and the ionosphere. The TEC values are also various at different puncture points where the propagation signals traverse the ionosphere. So considering the spatial variance, the phase errors can be modified as

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