Active And Passive Altimetry Algorithm Based On Signal Multi-domain Extension

The radio altimeter can provide accurate altitude information to the flight platform,which can not only guarantee the stable and safe flight of the platform,but also facil-itate the positioning and processing.Generally speaking,the altimeter is measured by active radar,which is mainly divided into three types according to the system:frequency modulated continuous wave(FMCW)type,quasi-frequency modulated continuous wave(FMICW)type and pulse radar altimeter.The commonly used altimetry method uses the method of extracting the echo front to measure the altimetry,not only the accuracy is not high,but also the echo signal is not fully utilized.Due to the change of active and passive altimetry scenarios,it is necessary to consider the altimetry model and algorithm from three dimensions:time,frequency and space.In this thesis,based on the current research status of altimetry at home and abroad,the altimetry algorithm is optimized from time,frequency and space to improve the signal utilization rate.High precision altimetry algorithms under active and passive altimetry models are respectively considered to improve the measurement accuracy to a certain ex-tent,which mainly includes the following aspects.Firstly,in the model of active altimetry,a wide beam is used to illuminate the ground,and the signal reaches the receiver after being reflected from the ground.Because the surface irradiation circle has a certain area,there are both reflection and scattering com-ponents in the echo signal.In this thesis,the ground echo signal is analyzed,the reflection component and the scattering component are modeled respectively,and the echo signal model is obtained.Secondly,the influence of the Angle of beam direction on the result of height mea-surement is discussed when the Angle of beam direction is skewed.In the time domain,the ground is divided into multiple equidistant rings,and the beam deflection Angle is judged and measured by the time-delay extension of the face mark,and then the height measurement value is obtained.In this thesis,the time-delay envelopment estimation method and the multi-objective time-delay estimation method are studied and compared respectively to analyze the echo signal and estimate the shortest and longest time-delay.A time delay extended height measurement method is proposed,that is,the shortest echo time delay and the longest echo time delay are used to measure the beam deflection Angle and height.The simulation results show that the proposed algorithm has higher precision than the traditional algorithm.Thirdly,in the frequency domain,the ground is divided into multiple equal Doppler bands,and the Doppler spectrum of the ground echo signal is used to estimate the beam deflection Angle.In this thesis,time-frequency analysis of ground echoes is carried out,and the beam deflection Angle is judged in the frequency domain.According to the beam deflection Angle,the range gate corresponding to the true height is obtained,and then the height estimation is obtained.Simulation results show that the method is accurate in estimating the beam deviation Angle and measuring the height.Finally,under the condition that the flight platform itself does not emit signals,a method of altimetry using external emitter signals in space is proposed.The platform re-ceives direct wave and non-direct wave,and the elevation Angle of the direct wave and the strongest non-direct wave is estimated respectively.Combined with the time difference between the two paths,the height of the receiving platform can be estimated.The prob-lem of height measurement is transformed into the problem of Angle estimation,which improves the accuracy of measurement and achieves the performance of low interception.The simulation results show that the new height measurement model has good perfor-mance.