Air Target Detection Study Based On Interferometry GNSS-R

With the cross of GNSS technology and other subject,the application of GNSS has been expanded.Remote sensing technology based on GNSS signal is paid more and more attention.This remote sensing method to achieve the target inversion by detecting the reflected GNSS signal and extracting information,such as material and shape of the target in the reflected signal.GNSS-R has a wide range of applications,including marine remote sensing,geological inversion,vegetation detection and so on.Among all kinds of applications,air target detection has gradually become a hot research in recent years.We often need C/A code of locally generated for processing GNSS-R signal.Considering the reversal of the navigation message,the time of coherent integration cannot be too long that resulting in the signal processing gain is not enough and the weak reflection signal cannot be detected.In order to solve this problem,this paper uses interferometry GNSS-R technology to detect air targets.The interferometry GNSS-R technology does not need to generate a local signal when processing the reflection signal,and directly coherent integration between the direct signal and the reflection signal.Due to the direct signal has the same navigation message with the reflected signal,so the coherent integration time will not be limited.First,the interferometry GNSS-R target detection system is constructed based on an exact understanding of the characteristics about the GNSS direct signal and the reflection signal.Then,this article added a preprocessing process to the reflection signal processing.The preprocessing includes the code Doppler shift compensation and the elimination of the direct component in the reflection signal.The code Doppler shift causes the change of the code rate,so we can adjust the signal rate to achieve the code Doppler shift compensation.In this paper,the elimination of the direct component in the reflection signal is realized by the adaptive filter.At the same time,the process of searching the reflection signal on delay-Doppler two dimensions is explored,and the calculation method of two dimensional correlation value is analyzed.Finally,an experimental verification of the interferometry GNSS-R target detection algorithm is carried out.The verification is divided into two stages,one is acquisition satellite signals of-135 dBm,-145 dBm,-150 dBm which is produced by Matlab.The experimental results show that the algorithm can detect the weak signal of-150 dBm.The other is to test the signal collected by the real environment.The results show that the interference GNSS-R algorithm can detect the signal reflected from the low-altitude and low-speed aircraft.