Research On Range Gating Technology For Ultrashort Pulse Laser Ranging

Satellite laser ranging technology is one of the most precision methods in geodetic measurement.It calculates the precise distance between the satellite and the observation station by measuring the flight time of the laser.Compared with the traditional laser ranging method,the ultra-short pulse laser ranging method with pulse width up to picosecond order can bring higher measurement accuracy.Single photon avalanche diode(SPAD),the photoelectric receiving detector of satellite laser ranging system,is easily affected by noise.Distance gating is a time filtering technique,which is turned on immediately before the arrival of the echo to minimize the probability of interference noise.Compared with the satellite laser ranging fixed station,TROS1000 of China Earthquake Administration has the advantages of high flexibility and convenient installation,but it also faces some problems such as small internal space and unstable module work.In order to improve the stability of range gating module on mobile satellite observation station under field working environment,a new range gating system is designed in this paper.The system adopts the new architecture of ARM+FPGA,and gives full play to the advantages of the two chips in parallel execution and floating point calculation.The parameter interpolation and range gating time calculation which originally depended on the upper computer were completely placed in the lower computer,and the upper computer only used to deliver ephemeris and result display,which increased the integration degree of the whole system and reduced the use space of the range gating system.The main contents of the article are as follows:(1)The development of satellite laser ranging technology,ultra-short pulse laser ranging technology,range gating technology and the realization method of range gating used by domestic and foreign stations are introduced.And then,the realization principle of range gating,interpolation parameter fitting method and backscattering avoidance principle are described in detail.(2)The hardware circuit and the overall logic architecture of the range gating system are redesigned,and the chip selection is completed.The hardware circuit design of the real-time clock module,storage module,computing module,comparison module and laser ignition module is described in detail.Finally,the connection mode between the two chips is introduced.(3)The software design of range gating system in this paper is introduced,including the design ideas and concrete implementation methods of the functions of upper computer interface,lower computer serial port reception,time synchronization,parameter fitting,range gating calculation,range gating writing,backscattering avoidance and so on.(4)Build a test platform,download the system to the chip and use the current satellite ephemeris for actual testing,including the running status of each module and the overall performance of the system.The results show that the timing sequence of receiving and receiving of FSMC bus is normal,and the running sequence of computing module,clock module and storage module is correct and stable.The UTC clock synchronization is normal,the interpolation parameter fitting accuracy of satellite ephemeris is below 0.002%,and the single real-time range gating calculation takes only 34.365?s,which can meet all existing observation frequencies.The backscattering avoidance module works normally and the ignition frequency drop rate is less than 1%.The output of the gated signal is fast and reliable,the output resolution can reach 5ns,and the overall performance meets the requirements of ultra-short pulse laser ranging.