The Research Of Signal Acquisition And Processing Technology For Hand-held Laser Ceilometer

Laser ceilometer is one of the normal equipment for observation of cloud base height. The laser ceilometer operating with shooting a set of laser pulses,recognizing the cloud-base by extracting the peak of the echo, and obtaining the height of the cloud-base by multiplying the round-trip time delay with the light speed. At present, the analog circuit is the most popular mode for information processing of the hand-held laser ceilometer, within the counting of the time delay of the transmitted monopulse by the counter, which may lead to false alarm or missing of the true value of the cloud-base height, as result the airport service was lower than the expectation. In this paper, a new project named the combinational logic circuit was proposed for the high-speed signal sampling system, which is installed in the end of laser receiver. In the new sampling system, the digital sampling of the echo was finished within the sequential control of the AD(analogue-to-digital) converter and the dual-port RAM by the combinational-logic-circuit. Furthermore, the multidimensional information processing method was applied in the ARM(Advanced RISC Machines), as result the cloud base height was more accurate than the current level. The main contributions of this thesis were concluded as follows:(1) The high-speed signal sampling project and the multidimensional information processing method were applied in the new hand held laser ceilometer, which can minimized the error of the measured cloud based height by comparison of the echo.(2) The 32bit ARM was applied as the microcontroller of the circuit of the system, the framework of the system was divided into 6 parts, and there are the sampling module, the processing module, the memory module, the communication module, the clock module and the power module. The sequential control of the sampling module was designed as the combinational-logic-circuit instead of the complex software control,which had reduced the load of the frequency for the ARM.(3) The software for digital high-speed sampling system was compiled by the Keil MDK4, and the functions of the software were finished by the visual C++, such as the storing by the EEPROM, the communication by the USART,etc. Furthermore, the multidimensional information processing method was designed to recognize the cloud-base height by the width, the height, and the echo power.(4) The software and the hardware of the system were tested, the functions of the new modules were verified, such as the high-speed sampling system , the storage system. Furthermore, the multidimensional information processing method was verified.The cloud within 4500 meter could be detected by the improved hand-held laser ceilometer, which also can store atmospheric echo with temporal information more than 100, whose sampling interval is 7.5 meters.The cloud base height was obtained by applying inversion algorithm to process atmospheric echo. Compared with the CHM 15K ceilometer, it shows that both of the results are basically identical. Eventually, improvement and prospect is proposed for exiting problems of the hardware and algorithm.