Optical remote sensing of surface roughness through the turbulent atmosphere

Using a CO(2), cw, coherent lidar, we have measured the surface roughness of diffuse targets through 1000 m of turbulent atmosphere. The technique measures the phase fluctuations of the speckle field at the receiver and relates the measured phase variance to the surface roughness. Measurements were made with aluminum targets that had been sandblasted with 8-, 16-, and 30-grit material and also with a flame-sprayed aluminum target. It was found that a linear relationship exists between the standard deviation (SD) of the unwrapped phase fluctuations and the SD of the target surface-height fluctuations. Good results were obtained with modest transmitter power and small receiver optics in just a few seconds of averaging time.