Time-delayed statistics for a bistatic coherent lidar operating in atmospheric turbulence

Effects of refractive turbulence on coherent laser radar

The leading-order effects of refractive turbulence are calculated for a general coherent laser radar with beam-angle and beam-offset misalignment. The effects of refractive turbulence are important for 10-microm operation in the atmospheric surface layer for typical daytime conditions and paths longer than 3 km. The effects for near-infrared and visible wavelengths are more pronounced. The behavior of different parameter regimes are related to the scintillation scales of the transmitted beam. In certain cases, the small-scale scintillation structure produces a measure of beam misalignment that is more sensitive than the free-space case. The phase approximation of the extended Huygens-Fresnel principle is shown to be correct in the limit of large path-integrated refractive turbulence.

Coherent summation of spatially distorted laser Doppler signals by using a two-dimensional heterodyne detector array

We report what is to our knowledge the first demonstration of phase-sensitive coherent summation of individual heterodyne detector array signals for the enhanced detection of spatially distorted laser Doppler returns. With the use of a 2 x 2 heterodyne detector array, the phase and amplitude of a time-varying speckle pattern was detected, and the signal-to-noise ratio of the Doppler shift estimate was shown to be improved by a factor of 2, depending on the extent of spatial coherence loss. These results are shown to agree with a first-order analysis and indicate the advantage of coherent summation for both short-range laser Doppler velocimetry and long-range atmospheric coherent lidar.

Useful receiver telescope diameter of ground-based and airborne 1-, 2-, and 10-microm coherent lidars in the presence of atmospheric refractive turbulence

The integrated effect of atmospheric refractive turbulence on ground-based and airborne 1-, 2-, and 10-microm coherent lidars with different geometries is calculated as a function of height by using altitude profiles of C(n)(2).