Hardware and software simulation of photon counting 3D lidar

In conditions with large amounts of clutter and low contrast target detection and identification is difficult using 2D images. The possibilities for automatic target detection increase drastically if 3D information is measured, through detection of planar surfaces and measurement of object dimensions. The ability to separate objects at different distances can also facilitate augmented presentation for operators. 3D measurement using stereo images perform well in open and urban areas, but has very limited capability to see behind obscurations as vegetation and camouflage netting. Laser systems based on time of flight (ToF) measurement for laser pulses from the laser to reflection at the target and back to the detector again are however able to detect a surface beneath foliage if only a small portion of the laser pulse penetrates the obscuration. Laser based systems also give better performance in darkness, in shadowed areas and for looking through windows. For distances longer than a few hundred meters a technology based on photon counting Geiger mode Avalanche Photo Diodes (GmAPD) is considered most suitable. This type of detector allows the highest range resolution, which is important to separate surfaces at different distances within the field of view for one pixel. Another important advantage is the extremely high sensitivity where the detector reacts to single photons. This allows lower laser pulse energy for the same maximum measurement range, extra important on flying platforms where weight and size are severely limited. An array detector 3D-lidar system has been simulated by scanning a photon counting sensor system based on a single pixel GmAPD. Measurements on a characterization target show exceptional range accuracy and range resolution. Measurements against a copse with carton and human targets show good penetration through obscurations and high potential for development of automatic target detection. Software simulations of photon counting 3D-lidar against a CAD-model of the characterization target give good correspondence with measurements. The software simulations allow parameter variations that can be used for better specifications of parameters for future array detector systems. Thoughts on how to develop the model to allow simulation of an UAV-mounted system are reported. The photon counting 3D lidar simulation shows the high performance possible with this technology. Hardware simulation with a single pixel scanning system has collected realistic data for testing of signal processing algorithms. Software simulations give data with good correspondence to the measurements and can be used to study the effects of variations in system parameters.