Range accuracy of a gated-viewing system as a function of the gate shift step size

Primarily, a Gated-Viewing (GV) system provides range gated imagery. By increasing the camera delay time from frame to frame, a so-called sliding gates sequence is obtained by which 3-D reconstruction is possible. An important parameter of a sliding gates sequence is the step size by which the gate is shifted. In order to reduce the total number of required images, this step size should be as large as possible without significantly degrading the range accuracy. In this paper we have studied the influence of the gate shift step size on the resulting range accuracy. Therefore, we have combined the Intevac Gated-Viewing detector M506 with a pulsed 1.57 µm illumination laser. The maximal laser pulse energy is 65 mJ. The target is a one-square-meter-plate at a distance of 500 m. The plate is laminated with a Spectralon layer having Lambertian reflection behavior with a homogeneous reflectance of 93 %. For the measurements, this plate was orientated diagonally to the line of sight of the sensor in order to provide a depth scenario. We have considered different combinations of the two parameters »gate length« (13.5 m, 23.25 m, 33 m) and »signal-to-noise ratio« (SNR) (2 dB, 3 dB, 5 dB, 6 dB, 7 dB, 8 dB). For each considered set of parameters, a sliding gates sequence of the target was recorded. Per range, 20 frames were collected. The gate shift step size was set to the minimal possible value, 75 cm. By skipping certain ranges, a sliding gates sequence with a larger gate shift step size is obtained. For example, skipping the ranges 2, 3, 5, 6, 8, 9,... (equivalent: taking the ranges 1, 4, 7, ...) results in a gate shift step size of 2.25 m. Finally, the range accuracies were derived as a function of the gate shift step size. Additionally, the influence of frame averaging on these functions was studied