Research On Balance Detection Method Of Space-based Heterodyne Inverse Synthetic Aperture Lidar

Inverse Synthetic Aperture Lidar(ISAL)is an active imaging radar that combines synthetic aperture technology with lidar technology.High-precision monitoring imaging of space targets is of great practical value,space-based ISAL imaging has extremely high resolution and is not limited by distance,and there is no atmospheric disturbance in space,so space-based ISAL has great advantages in space-based long distance active imaging.However,the space-based ISAL imaging distance is long,and the laser emission power is limited,resulting in a very weak echo signal,the core difficulty is the low detection sensitivity.This paper has carried out a series of research work around the research goal of improving the detection sensitivity of space-based ISAL.The main work of this paper is as follows.Firstly,the basic principle of ISAL imaging is introduced,and the space-based ISAL imaging model is analyzed.The advantages and disadvantages of the two signal modulation systems of space-based ISAL imaging,the chirp system and the phase encoding system,are analyzed.The space-based ISAL signal receiving system and the system signal-to-noise ratio are analyzed,and it is concluded that the space-based ISAL needs to adopt a high-sensitivity balance detection mode.The basic flow of the ISAL imaging algorithm and the composition of a set of space-based ISAL systems with a wavelength of 1550 nm are given.Then the space-based ISAL high-sensitivity balance detection method was studied.A set of parameters is given,and the signal-to-noise ratio is calculated for the spacebased ISAL system.The calculation results show that the signal-to-noise ratio is very low,and the detection sensitivity must be improved.The imaging simulation experiment was carried out with a distance of 100 km,and the simulation imaging results with signal-to-noise ratio of-14 dB and-5.5dB were given.The performance analysis of the space-based ISAL imaging system balance detector was carried out.The performance comparison experiments of two balance detectors,PIN and APD,were carried out.The results show that the APD balance detector is suitable for the spacebased ISAI imaging system.Finally,a balance detection method based on frequency up-conversion is proposed,which can greatly improve the detection capability of the system.The signal light and the local oscillator light are first subjected to frequency up-conversion and then balanced detection.The experimental results show that the signal can be coherently preserved,which verifies the feasibility of this method.