In-line type micropulse lidar with an annular beam: theoretical approach.

An in-line type micropulse lidar (MPL) with an annular beam was designed and the transmitting and receiving characteristics were analyzed. Because the in-line MPL utilizes a common telescope for a transmitter and a receiver and the annular beam always overlaps with the receiver's field of view (FOV), it can measure near-range lidar echoes with a narrow FOV. The transmitting annular beam changes its shape to a nearly nondiffractive beam through propagation. It improves the spatial resolution of the lidar observation. The receiving characteristics showed the ideal lidar echo variation, which was inversely proportional to the square of the distance the beam propagated, even if it was in the near range.