Atmospheric Radiowave Propagation Effects On Performance Of Spaceborne Synthetic Aperture Radar

The performance of spaceborne synthetic aperture radar (SAR) will be affected when the radiowave propagates in atmosphere. Using atmospheric refractive theory and the apparent target concept which is put forward in the course of analysis, the radiowave propagation effects on phase time-delay and spatial resolution of SAR in spherically stratified atmosphere are studied in this paper, and for the first time using the ionospheric electron density profiles and the lower atmospheric refractivity pofles of Manzhouli, Lanzhou, and Haikou in different times, for P,L,and X bands, the atmospheric excessive phase time-delay and the difference between side and middle in the antenna beam are calculated, relative to vacuum time-delay and group time-delay measured in the application, respectively, and the effects on spatial resolution in the range of synthetic aperture length are also calculated. Moreover, the difference of atmospheric excessive phase time-delay among the synthetic aperture length is fit by the polynomials including frequency and ground range deviating from middle, and the residual error of atmospheric excessive time-delay produced by atmospheric refrective index error is also given. In addition, the methods of atmospheric excessive phase time-delay in two and three dimensional non-spherically stratified atmospheres are presented. Considering the ionospheric refractive index in geomagnetic field, the radiowave polarization plane rotation has been calculated. For linear frequency modulation pulse signal, the expression of Doppler shift error due to ionospheric dispersion characteristics is derived. Quantitative simulation results show that atmospheric radiowave propagation effects on performance of SAR should be considered in P band and can be neglected in L or X band.