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Signal processing techniques for heterodyne differential absorption lidar

Different methods of energy estimation for a differential absorption lidar (DIAL) system at NASA Langley Research Center in Virginia are investigated in this paper. The system is a 2- &mgr;m wavelength coherent Doppler lidar called VALIDAR that has been traditionally used for measuring wind. Recent advances in laser wavelength control have allowed the new use of this lidar for measuring atmospheric CO2 concentration by a DIAL technique. In order to realize accurate DIAL measurements, optimal signal processing techniques are required to represent the energy of the heterodyned backscatter signals. The noise energy was estimated by minimizing the mean square error in its estimate and was used to normalize its adverse influence on accurate estimation of the concentration of CO2 in the atmosphere. The impact of different methods on the statistics of CO2 concentration measurements is compared.