Heterodyne lidar with a laser receiver

It is shown that the reception of an echo signal by a frequency modulated laser gives rise to beats of the laser radiation intensity. The peak-to-peak amplitude of the beats is governed by the characteristics of the propagation path and the frequency is proportional to the difference between the instantaneous frequencies of the transmitted and reflected signals. The results are given of experimental investigations carried out over atmospheric paths of different length using a CO₂ laser. Measurements are reported of the threshold sensitivity to an external signal in the case of coherent laser reception.