We present an active optical synthetic aperture-imaging system. A phase-step digital holographic setup is used as a wavefront sensor in the far field. The overlap of the holograms enables the estimation and compensation of their relative positions and phase with a speckle cross-correlation algorithm. Experimental results on a short-range synthetic aperture setup at 633 nm are presented that are based on 128 x 128 holograms. The synthesis is executed in one direction by means of rotation of the object. Test images show a significant gain of resolution in the synthesis direction. Processing errors are estimated through experiment. Random processing errors of a synthetic pupil composed of 33 merged holograms are negligible, but biases induced by unknown optical aberrations ofthe reference wave induce defocusing and astigmatism.

Clear-air turbulence could be detected at long range using a UV lidar. Because the vertical speed cannot be retrieved from Doppler shift analysis at long range, the turbulence detection is based on the measurement of molecular density fluctuation associated with the turbulent wind. After an optimization of the characteristics of the candidate UV lidar, we present an evaluation of the detection range and of the false alarm rate and missed alarm rate depending on the altitude and vertical velocity root mean square. This study shows that 96% of turbulence with vertical velocity leading to dislodging of unsecured objects in the airplane can be detected at 15 km using a 2 W laser at 355 nm with a false alarm rate of 0.18 per flight hour.

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