In this paper we present a technique for calibration of a lidar emitting into the atmosphere sounding pulses of micro–Joule energy that allows for the purely statistical nature of return signals (recorded in the photon counting mode). Some results of measurements of the backscattering coefficient in the atmosphere up to several hundred meters are presented and the capability of the lidar to detect invisible atmospheric inhomogeneities is demonstrated. Prospects of using such an eye–safe lidar in the environmental monitoring avoiding damage from laser radiation is discussed.