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Inversion Algorithm and Precision Analysis for AMCW DIAL Measurements of CO2

Based on the theory of differential absorption, an amplitude modulation continuous wave (AMCW) differential absorption lidar (DIAL) aiming to measure the concentrations of CO2 in the lower troposphere has been developed. The analysis methods of received envelope signals were discussed in detail first. Three different cumulative averaging methods were also analyzed and the compared results pointed out that the orders have little impact on our system. Moreover, the limitation in the improvement of standard deviation of the ln (ratio) through signal cumulative averaging was also analyzed, which showed departures from theoretic N-1/2 dependence improvement. Then a novel precision estimate method was proposed, which showed the resolution a 1.1% standard deviation or less in our system. The trend of CO2 concentrations during two days in the urban district of Shanghai was presented in the end.