ESTIMATE OPTIMIZATION PARAMETERS FOR INCOHERENT BACKSCATTER HETERODYNE LIDAR

Heterodyne lidar estimates are a function of a number of experimental parameters, some of which can be adjusted or tuned to optimize statist ical precision. Here we refer the precision to the theoretical limit f or optical measurements of return power and Doppler shift and investig ate the conditions for optimization using established theoretical expr essions for the standard deviation of various estimates. Tuning is cha racterized by a degeneracy parameter (the photocount per fade). For es timators that filter or resolve the return, it is shown that optimal t uning is achieved at wideband signal-to-noise ratios less than 0 dB an d detected signal levels corresponding to more than a single effective photocount. Estimators that do not filter are predictably at a disadv antage when the signal bandwidth range gate product is low. The minimu m standard deviation available from an optimally tuned heterodyne syst em is found to be greater than twice the limit. (C) 1997 Optical Socie ty of America.