A Theoretical Study of a Two-Wavelength Lidar Technique for the Measurement of Atmospheric Temperature Profiles

C. Laurence Korb NASA/Goddard Space Flight Center, Greenbelt, MD 20771

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Chi Y. Weng Science Systems and Applications, Inc., Seabrook, MD 20801

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Abstract

The theory of differential absorption lidar measurements for lines with a Voigt profile is given and applied to a two-wavelength technique for measuring the atmospheric temperature profile using a high J line in the oxygen A band. Explicit expressions for the temperature and pressure dependence of the absorption coefficient are developed for lines with a Voigt profile. An iteration procedure for calculating the temperature for narrow laser bandwidths is described which has an accuracy better than 0.2 K for bandwidths < 0.01 cm−1. To reduce the errors in lidar measurements due to uncertainties in pressure, we describe a method for estimating the pressure from the temperature profile. We also describe a procedure for extending the differential absorption technique to the case of finite laser bandwidth with good accuracy. Simulation results show that a knowledge of the laser frequency is needed to 0.005 cm−1 for accurate temperature measurements. Evaluation of the sensitivity for both ground- and Shuttle-based measurements shows accuracies generally better than 1 K. This technique allows up to an order of magnitude improvement in sensitivity compared to other differential absorption lidar techniques.

Abstract

The theory of differential absorption lidar measurements for lines with a Voigt profile is given and applied to a two-wavelength technique for measuring the atmospheric temperature profile using a high J line in the oxygen A band. Explicit expressions for the temperature and pressure dependence of the absorption coefficient are developed for lines with a Voigt profile. An iteration procedure for calculating the temperature for narrow laser bandwidths is described which has an accuracy better than 0.2 K for bandwidths < 0.01 cm−1. To reduce the errors in lidar measurements due to uncertainties in pressure, we describe a method for estimating the pressure from the temperature profile. We also describe a procedure for extending the differential absorption technique to the case of finite laser bandwidth with good accuracy. Simulation results show that a knowledge of the laser frequency is needed to 0.005 cm−1 for accurate temperature measurements. Evaluation of the sensitivity for both ground- and Shuttle-based measurements shows accuracies generally better than 1 K. This technique allows up to an order of magnitude improvement in sensitivity compared to other differential absorption lidar techniques.

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