To synchronize the PMT and CCD camera, synchronization control function is added into the hardware module. When
light pulses are transmitted to the target, the pulse laser sends triggering signals to hardware module. The triggering signals from laser are screened by a comparator to eliminate interference signals. Then the hardware module forwards the trigger to the CCD camera which captures images immediately. Next, after a period of time which depends on the distance from target to PMT, the reflected light pulses reach the PMT which convert them into electrical pulses. At this time, the synchronization control module in FPGA starts the DAQ progress for capturing PMT signal. For example, the delay time is ~1667 ns when the distance is 1 km. The delay time and other acquisition parameters are set by software through USB interface and latched in the FPGA.