Lead-angle effects in turbulence-compensating reciprocity tracking systems

A description is presented of a simple approach which can be used to include violations of strict isoplanatism in the design and analysis of tracking systems that attempt to compensate for atmospheric turbulence degradation of a transmitted laser beam. The effects of isoplanatic patch size become important when a beam is to be sent to a distant, fast-moving target. The effects arise in connection with the required lead angle between the tracker line-of-sight and the laser beam, and the finite propagation time of the beam from the system aperture to the turbulent medium. A control-loop is presented which provides a simple way of extending isoplanatic patch calculations to include the tracking system transfer function.