The applicability of optimal Markovian filtration for mono-pulse single-frequency aerosol sounding using an airborne coherent IR-lidar based on the Markovian model of altitude fluctuations of aerosol backscattering coefficient ba(z) smoothed by a laser pulse is discussed. The algorithms of optimal estimation on the (ba(z) realization and its variance are derived. The sounding efficiency is analysed by means of numerical simulations for two ideal lidars with a moderate energy potential for nadir sounding from altitudes 9 and 15 km.