Experimental comparison of a Gated-Viewing system and a 3-D Flash LADAR system in terms of range precision under different turbulence conditions

For security and military applications, long-range automatic target recognition is a very important task. Therefore, in addition to a 2-D passive or active intensity image, 3-D information of a target is desirable. Besides a LADAR system, also a Gated-Viewing (GV) system can provide depth information by simply sliding the gate through the scenery. In this paper, the GV camera LIVARÒ 500 (Intevac, 640 × 480 pixels (binning mode), EBCMOS) is compared to a 3-D Flash LADAR camera (Advanced Scientific Concepts, 128 × 128 pixels, InGaAs APD) in terms of range precision. The sliding gates method requires several GV images (several laser pulses) with stepwise increased camera delay times. For the 3-D Flash LADAR camera, one laser pulse is sufficient because, for each pixel, the range is determined by the time-of-flight method. We have combined both cameras with the same pulsed laser illuminator with a wavelength of 1.57 ?m. The maximal laser pulse energy was 67 mJ. We have conducted field measurements at different times of day. Two reflectance panels and a vehicle at a distance of 2 km were recorded. The plates were positioned diagonal to the line of sight with an angle of about 45 degrees. They were used to determine the range precision, defined as the error standard deviation. Atmospheric turbulence, i.e. refractive index fluctuation along the propagation path, affects the laser pulse resulting in a degraded intensity image. The laser scintillometer BLS 900 (Scintec) measured the refractive index structure parameter Cn 2 along the propagation path. The comparison of the two cameras was carried out under different turbulence conditions.