Accuracy of lateral displacement sensing in atmospheric turbulence using a retroreflector and a position-sensitive detector
The displacement sensing accuracy of the reflected beam method in a turbulent environment is studied experimentally. The method includes an illuminated corner cube retroreflector (CCR) and a lateral effect photodiode (LEP) by which the image position of the CCR is detected. The results show turbulence (Cn approximately 5 X 10-7 m-1/3) limited measurement resolution to vary from 0.6 to 9 mm (standard deviation) in the distance range from 50 to 300 m. The result is 1.4 to 2.1 times worse than that measured for the direct beam sensor in the same atmospheric conditions. The CCR used is found to have no systematic effect on the achievable resolution but the method is found to be very sensitive to receiver defocusing. An approximately 10-fold increase in standard deviation is observed when the receiver is defocused by 2%. The possibility to average out part of the angular fluctuations by using multiple CCRs is verified. By using two CCRs instead of one, when positioned 1.3 m apart at a distance of 150 m, a resolution better by 22% is achieved. The averaging in the case of the LEP, however, is not effective because the noncorrelated intensity fluctuations of the reflections from the different CCRs cnacel the averaging effect.