Modeling And Signal Processing Of The Linear Three-dimensional Laser Imaging Radar System

Compared to the current three-dimensional radar imaging technologies (such as synthetic aperture radar, infrared, millimeter wave, visible light, etc.), laser technology can achieve high-precision data directly, including more extensive image information (3D range images, grayscale images, etc.) and better anti-jamming ability (such as electromagnetic, backgrounds, and sunlight). Because of this, the three-dimensional imaging laser radar is becoming an important aspect of the development of active imaging probe, which got our military and foreign military attention. However, the laser imaging technology is limited to the size of the detector array and scanning configuration. It is urgent to break that the scanning speed and accuracy is difficult to obtain further improvement in current system.This paper launched a CDMA-based three-dimensional laser imaging radar detection technology from modulation, detection and demodulation, combined with reconstruction and recovery, in terms of the deficiency of the conventional three-dimensional laser imaging technology. Proposed a new three-dimensional laser imaging method based on laser modulation techniques, which achieved measuring M *N pixels simultaneously by M receive detectors and N segments modulated laser, in order to achieve high-resolution laser imaging technology. Through the studies of three-dimensional laser array radar system, this paper established a simulation system which could realistically simulate the key features of the three-dimensional laser radar system to help the study of the signal processing algorithms. And proposed a set of signal processing solutions, including weak signal extraction, waveform decomposition, signal demodulation, error detection and correction, image signal filtering and enhancement algorithms for elementary radar systems. The system proposed by this paper can achieve faster measurement speed, higher accuracy and greater scalability by the coding segment N laser modulation, the receiver with M detectors simultaneously measure the M*N data points, which greatly extends the scalability of the system.This paper made a thorough research of CDMA linear three-dimensional imaging laser radar technology. First, analyzed and modelled the system, including laser transmission system, atmospheric transmission, ground target and reception & detection system. On this basis, elaborated the idea of coding and multiplexing algorithm, introducing the principle and implementation of laser-multiplexed orthogonal code at the same time.As for the full waveform data, the treatment could be concluded. First of all, remove additive noise using fractional Fourier transform and remove multiplicative noise using signal accumulation according to correlation characteristics and coding features. Secondly, use LM algorithm to decomposition and fitting the full waveform data, in order to get the accurate position of the echo pulse. Instead of the Gaussian function, a more precise model is used during the fitting operation, so that we can get a better fitting result. Thirdly, do the correlation calculation using the specified encoding template and the received echo signal. This will demodulate the echo signal. Finally, do the error checking and correction with Hamming.Multivariate linear weighted average generalized morphological filtering is used to remove the speckle noise. This method can greatly improve the speckle noise suppress ability while maintain the edge of the image well. On the other hand, as the laser echo signal is weak and noise also decrease the signal intensity, which is reflected in the image pixel gray value smaller and concentrated in a small range, it is necessary to increase the relative gray value of each point in the undistorted condition. Based on the improved SFLA, the image enhancement algorithm we use has a fast search speed, wide range, which can quickly achieve adaptive image enhancement.