FMCW lidar for multiple-target sounding

Continuous-Wave lidars are constantly evolving in order to achieve the best performances with low power and low cost. Frequency-modulated continuous-wave (FMCW) lidar is a well-known type of lidar used for solid-target detection and ranging with high spatial resolution. The extension of this lidar technique to the probing of distributed media (aerosols, smoke or exhaust fumes) has recently been proposed by the authors. The main drawback in measuring extended or distributed targets with a conventional FMCW signal is the loss of information that occurs in the retrieved signal, as it suffers a bandpass filtering in the detection process. This implies the practical impossibility of recovering the complete information about the target spatial distribution. A shift of the sub-carrier FM modulating signal to baseband can avoid these effects and the desired information can be satisfactorily retrieved if the emitted signal is adequately chosen to avoid sum-frequency components distortion. A theoretical formulation has been developed and tested by sounding a distributed medium composed of two narrow solid targets, which is analyzed in different configurations by changing the distance among them. The medium is probed with both the classical sub-carrier FM bandpass signal and with the baseband one previously proposed. The experimental results are compared with the corresponding simulations in order to assess them.