Lidar return signals for coaxial and noncoaxial systems with central obstruction.

The return signal of coaxial and noncoaxial lidar systems with central obstruction has been calculated by integration of the irradiance in the focal plane. As in the coaxial unobstructed case, a small detector in the focal plane allows a geometrical compression of the detector signal dynamics. In coaxial systems, the shadow cast by the obstruction results in a reduction of the near signal. In noncoaxial arrangements a signal reduction occurs for distances that depend on the transmitter-receiver separation and the inclination angle, whereas the influence of an obstruction is almost negligible. Adequate signals can be obtained from short to long distances with both types of geometry.