<title>Minimization of systematic errors at lidar profile restitution of atmospheric gas concentrations by the differential absorption method</title>

Abstract

This work aims at studying the sources of the errors in restitution of atmospheric gas concentration profiles and the methods to minimize them. It is seen that the water vapor absorption line contour is significantly distorted by the apparatus function of the laser source positioned at the altitudes above 5 km. the results of performed numerical calculations with the model absorption lines show that it is more efficient to use the less intensive absorption lines. The studies of temperature sensitivity show that it is more reasonable to use the less intensive absorption lines. It is seen that the use in sensing of intensive lines of water vapor absorption at S₀= 0.5 cm^-1/g cm^-2 leads to significant errors in <i>a priori </i>calculations of the absorption coefficient profile due to the influence of humidity variations at &#916;V_e> 0.03 cm^-1 in winter and especially in summer. At S₀= 0.1 cm^-1 /g cm^-2 and &#916;&#965;_e < 0.03 cm^-1, errors practically do not exceed 1 percent for almost the entire altitudinal interval of 0-10 km. We have established that disregard to the measured line shift of water vapor absorption, which equals 694.38 nm, and calculated <i>CO</i> absorption line shift, 2086.322 cm^-1, at the system tuned into the centre of the Lorentz contour of <i>H₂0</i> and <i>CO</i> absorption lines, results in the errors that reach 20% at the altitude of 15 km. At the tuning into the Doppler contour, errors are largest in the ground layer (2-3%) and become smaller with the altitude.