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An a Posteriori Method Based On Photo-Acoustic Cell Information to Correct for Lidar Transmitter Spectral Shift: Application to Atmospheric CO2 Differential Absorption Lidar Measurements
Volume 61, Number 10 (Oct. 2007) Page 1068-1075
Gibert, Fabien; Marnas, Fabien; Edouart, Dimitri; Flamant, Pierre H.
An a posteriori corrective method based on photo-acoustic cell (PAC) information is proposed to correct for laser transmitter spectral shift during atmospheric CO2 measurements by 2 μm heterodyne differential absorption lidar (HDIAL) technique. The method for using the PAC signal to retrieve the actual atmospheric CO2 absorption is presented in detail. This issue is tackled using a weighting function. The performance of the proposed corrective method is discussed and the various sources of error associated with the PAC signal are investigated. For 300 shots averaged and a frequency shift (from the CO2 absorption line center) lower than the CO2 absorption line half-width, the relative error on HDIAL CO2 mixing ratio measurements is lower than 1.3%. The corrective method is validated in absolute value by comparison between HDIAL and in situ sensor measurements of CO2.