Abstract

In the conduct of a LIDAR experiment, one is always limited at the short range end by the distance required for the transmitted beam and the receiver field of view to overlap. When return signals are very large this blind spot can be advantageous in that it protects the receiver from saturation by the very strong near return. However in the limit of weak signals it would be very attractive to be able to see at short ranges before the inverse square law has greatly attenuated the signal. In any case it is usually desirable to operate the LIDAR receiver with a very narrow field of view in order to minimize the background signal due to scattered solar flux. Reducing the field of view of the receiver, however, increases the range at which total overlap is achieved as well as aggrevating the sensitivity of the system to misalignment. A model has been developed which calculates the degree of overlap of a LIDAR system as a function of range. Using this model one can show that under some circumstances in which the receiver and beam are misaligned, the form of the overlap function can affect the interpretation of differential absorption LIDAR (DIAL) data giving rise to substantial errors which may be of either sign.