Study Of Multi-feature Detection Techniques For Slowly Moving Targets Based On Multi-channel SAR Images

Multitemporal images of the same scene can be available in an efficient approach with multi-channel synthetic aperture radar(SAR)systems,and the spatial and temporal relationship among these complex images is significant to improve moving target indication(MTI)performance and location accuracy.Nowadays,MTI with multi-channel SAR systems plays a critical role in observing military intelligence and monitoring traffic activities.For the radar systems,the Doppler frequency of clutter reflected from observation scenes is spread because of the platform motion.The slowly moving targets are obscured by clutter.Thus,clutter rejection is necessary for MTI.Since clutter is virtually heterogeneous,spatially and temporally decorrelated,and the clutter space-time spectrum is sensitive to the angle of radar view in the oblique looking mode,plus radar system's amplitude and phase errors,clutter suppression ability usually declines.This situation leads to a high detection probability of false alarms(PFA)for MTI in heterogeneous background and a worse minimum detectable velocity(MDV)of moving target.To address the issues,we join the multiple features of complex multi-channel SAR images,i.e.,signal magnitude and phase,interferometric magnitude and phase,adaptive filtering response loss,and the ship wakes,to improve detection performance for the slowly moving targets in heterogeneous background in this dissertation.The main study aspects can be summarized as follows:1.For ground MTI(GMTI)in heterogeneous terrains,most existing detectors based on the magnitude after clutter suppression processing would have a high PFA and difficulty in detecting the slowly moving and low signal-to-clutter ratio(SNR)targets.To address the issue,a two-step detection approach based on the adaptive filtering response loss for multi-channel SAR-GMTI systems is developed.At first,we reject clutter based on the robust minimum variance metric and apply the magnitude-based detection with a relatively low detection threshold in order to increase target detection probability.Then,a complementary detector based on the output power loss in the clutter rejection procedure is performed to reduce false alarms.To obtain the adaptive detection thresholds,the statistics of the output power loss and the overall detection approach are analyzed theoretically.The simulation and experimental results demonstrate that the proposed detection approach can improve target detection performance for the low SNR moving targets in heterogeneous background and achieve a better MDV compared with the generalized likelihood ratio test (GLRT),two-step detector by joining the magnitude and interferometric phase,and the interferometric magnitude and phase(IMP)method.2.For the sea-clutter background,most moving target detection methods based on the along-track interferometric(ATI)phase would have a high PFA and suffer from the blind-speed response in the detection.To deal with the problem,we propose a novel method to detect the active marine targets by fusing the interferometric magnitude and phase adaptively for dual-channel ATI SAR systems.At first,an interferometric bilateral filter is designed to smooth the random noises and locally adapt to the spatial structure of the interferogram.Then,the target detection metric is constructed by adaptively fusing the interferometric magnitude and phase based on the Gaussian kernel function.Furthermore,the probability density function(pdf)of the metric is derived to facilitate the detection threshold computation.The theoretical analysis indicates that the proposed target detection metric can mitigate the blind-speed detection problem by adaptively regressing into a magnitude-based test toward the targets moving at the blind speeds.For the targets far from the blind-speed zones,the proposed method can make full use of interferometric magnitude and phase to enhance the target-to-background contrast and thus to yield a fine detection result.Experimental results show that the interferometric bilateral filter can smooth noises and is helpful for applying ATI techniques.In addition,the results validate the superiorities of the proposed method in detecting blind-speed and low SNR targets from sea background.3.Detecting moving ships of low signal-to-clutter ratio(SCR)is a challenging task in SAR images.To solve the issue,a ship detection method with the assistance of wakes features in ATI-SAR systems is proposed.First,the interferometric magnitude,phase and physical shape of ship wakes are utilized to detect moving ship wake regions.Based on the results,the ship speed is estimated by using the Kelvin wave property.Then,the position and ATI templates for the ship under detection are constructed by using the ship speed estimates and the geometrical position of the wakes.At the same time,a multi-feature test is designed to detect the potential moving ships with a relatively low detection threshold in the complex interferogram.In the following,the potential moving ships that are unmatched with the constructed templates are regarded as false alarms and thus to be eliminated from the detection results.Simulations show that the proposed method can improve detection performance for the low SCR moving ships in the sea environment.