The impacts of ionospheric scintillation on geosynchronous synthetic aperture radar（GEO SAR）focusing is studied based on the multiple phase screen（MPS）theory.The power spectrum density of electron irregularities is first modified according to the ionospheric anisotropy.Then propagation wave equations in random medium are deduced in the case of oblique incidence in GEO SAR.The amplitude and phase errors induced by the random electron fluctuations are generated by the iterated MPS simulations and are superimposed into the GEO SAR signals.Through the following imaging and evaluation,the effects of the anisotropic ionospheric scintallition on GEO SAR are assessed.At last,the optimized integration time under different ionospheric scintillation conditions are recommended through Monte Carlo experiments.It is concluded that,greater ionospheric fluctuations and longer integration time will result in more severe deterioration,even no focus at all in the worst case.
Bistatic SAR（Bi SAR）with illuminators of opportunity is a kind of flexible SAR system that consists of non-cooperative transmitters and a stationary or moving receiver,as Figure 1shows.In recent years,notable efforts have been made to promote the development of this kind of system.Progress regarding Bi SAR with navigation satellites as transmitters before 2015,including the related theory and practice,has been well reviewed by Antoniou et al.and can be referred from[1].This paper reviews some of the progress in 2015and 2016,including novel signal processing approaches,advanced Bi SAR system configurations and potentially
We propose a new type of dispersion flattening technology, which can generate an ultra-flat group velocity dispersion profile with five and six zero-dispersion wavelengths(ZDWs). The dispersion value varies from-0.15 to 0.35 ps/(nm·km) from 4 to 8 μm, which to the best of our knowledge is the flattest one reported so far, and the dispersion flatness is improved by more than an order of magnitude. We explain the principle of producing six ZDWs. Mode distribution in this waveguide is made stable over a wide bandwidth. General guidelines to systematically control the dispersion value, sign, and slope are provided, and one can achieve the desired dispersion by properly adjusting the structural parameters. Fabrication tolerance of this waveguide is also examined.
Dear editor,Geosynchronous synthetic aperture radar(GEO SAR)[1,2]has an inclined geosynchronous orbit of around 36000 km,which leads to its short revisit time of around 24 hours and a wide coverage of up to approximately one third of the Earth surface.Its long integration time guarantees the fine resolution.Thus,GEO SAR owns the promising capability of providing images with the high resolution,
Xichao DONGCheng HUWeiming TIANTian ZHANGYuanhao LI
