On the bases of analyzing triangle wave form modulated LFM, the method of using DDR (Dual Channel Directional Doppler range) technique to eliminate the influence of speed to range is presented.

In the implementation, we used the multiprocessing method in QNX to analyze the general flow chart of system, and divided the realization of dual downstream channel into three modules.

To study the method to detect trace arsenic and mercury in sea water in the same time with dual channel atomic fluorescence.