Clutter Analysis of the Range-Doppler Spectra under the Influence of Typhoon

The property of over the horizon (OTH) allows the HF surface (ground) wave radar system to be used in a variety of maritime applications. In terms of the location of Taiwan, ionospheric clutter which may limit the system performance occasionally appears in the radar spectrum, and this is another way to obtain the ionosphere features. As a kind of severe weathers, typhoon which is closely related to ionospheric disturbances may generate the powerful damage, this attracts our research interests. However, most ionospheric observation is difficult in continuous observation of typhoons. The aim of this study is to explore the change of ionospheric clutter patterns through the Range-Doppler (RD) spectra under the typhoon influence. In order to determine the morphologies of ionospheric clutters, the image processing algorithm was used for ionospheric signals identification and implemented to make comparison with corresponding typhoon records during the same period. Finally, the statistics of the spatial-temporal characteristics and clutter patterns of ionosphere before and after typhoon can be obtained. In this study, the ionospheric features were investigated by ionospheric clutters of the RD spectra. The results show that when the Typhoon Soulik approached Taiwan in 2013, the morphologies of ionospheric clutter were getting greatly different. The proportion of band-like ionospheric clutters under the effects increased greatly, which is highly likely connecting to the unstable ionosphere more unstable. Regarding the possible physical mechanism, the lower atmospheric disturbances created by typhoon were possibly transmitted to the ionosphere altitude in the format of acoustic gravity waves (AGWs) which may result in unstable ionosphere and plasma irregularities.