Research On Radar Imaging Technology Of GNSS-R Navigation Signal

With the development of Global Navigation Satellite System(GNSS),the research on Satellite reflection signal technology is also deepening.It not only completes remote sensing detection,such as the detection of oil spill and sea ice,high-accuracy sea surface,soil moisture detection,etc.,but also provides a new passive detection method for aerial targets and ground observation imaging.Some scholars have proposed the concept of Global Navigation Satellite system-bistatic SAR System based on Global Navigation Satellite System,which the transmitters are mounted on navigation satellites,and the receivers are fixed on the ground or mounted on moving platforms to form a bistatic SAR system.As a multistatic passive radar detection method,it has the advantages of complete coverage,all time,all weather,strong adaptability to severe weather environment,little influence of day and night environmental factors,etc.,and has great research space and broad development prospects.This paper mainly studies radar imaging technology based on GNSS-R satellite navigation signal.Combining with GNSS satellite navigation system and the basic theory of bistatic SAR imaging,the research contents include the basic theory of GNSS-BiSAR imaging,the GPS satellite orbit characteristics and coverage analysis,the echo signal model and imaging algorithm of GNSS-BiSAR for ground receiver and satellite transmitter,signal echo model and imaging algorithm based on space-variant geometric configuration for medium earth orbit satellite transmitters and low earth orbit satellite receivers.The primary work of the dissertation includes:Firstly,the important parameters such as pulse repetition frequency and doppler characteristic are deduced and analyzed.The detection power of navigation signal is discussed by the use of the bistatic radar equation.By means of the ambiguity function based on bistatic geometric configuration,the spatial resolution characteristics are explained intuitively.The GPS satellite orbit parameters are studied,and the preset scene is established by using STK software.The multibistatic coverage analysis provides a theoretical basis for the realization of imaging algorithms in the following chapters.Secondly,the observation geometry and motion characteristics of the GNSS-BiSAR model for ground receiver and satellite transmitter are studied.This paper expounds the GPS C/A phase coded echo signal and image reconstruction algorithm under the "non-stop-go" hypothesis.The preset scene region is established for multistatic GNSS-BiSAR observation geometry.The simulation experiment of multi-satellite simultaneous observation and imaging algorithm is completed,which brings the possibility of multi-angle image fusion.In order to solve the problem of small bandwidth and poor range resolution of GNSS signal,pseudo-random code is used to complete spectrum splicing and spectrum equalization,which can significantly improve the imaging effect.Finally,the transceiver trajectory is not parallel and the movement speed of the platform is not the same,which brings some difficulties to the imaging.The two dimensional spectrum of the signal based on space-variant geometry is derived in detail.The improved range doppler method,backward projection algorithm and improved technology inversion imaging algorithm based on space-variant configuration are presented.