Heterodyne lidar estimates are a function of a number of experimental parameters, some of which can be adjusted or tuned to optimize statistical precision. Here we refer the precision to the theoretical limit for optical measurements of return power and Doppler shift and investigate the conditions for optimization using established theoretical expressions for the standard deviation of various estimates. Tuning is characterized by a degeneracy parameter (the photocount per fade). For estimators that filter or resolve the return, it is shown that optimal tuning is achieved at wideband signal-to-noise ratios less than 0 dB and detected signal levels corresponding to more than a single effective photocount. Estimators that do not filter are predictably at a disadvantage when the signal bandwidth range gate product is low. The minimum standard deviation available from an optimally tuned heterodyne system is found to be greater than twice the limit. (C) 1997 Optical Society of America.
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