Outdoor single-photon counting panoramic 3D imaging

Single-photon counting lidar using Geiger-mode avalanche photodiode (GmAPD) arrays can provide high resolution 3D images at kilometer stand-off distances through coincidence processing. 3D data is useful for detection and identification of targets, especially those so occluded by vegetation that only small patches, smaller than the instantaneous field-of-view of a sensor pixel, have free line-of-sight. To cover an area of interest, e.g. the edge of a forest, with spatial resolution high enough to identify targets, a multi-megapixel 3D image is needed. Current GmAPD arrays are limited to tens of kilopixels. Even if the technical challenges of larger arrays could be solved, the necessary pulse energy per pixel will still limit the effective number of pixels at longer ranges, especially if nominal ocular hazard distance (NOHD) is a concern or if short pulse fiber lasers should be used. Thus scanning of the sensor field-of-view will probably always be necessary. In this paper we describe activities at FOI to explore the potential of single-photon counting panoramic 3D imaging using a GmAPD array detector. Results from outdoor experiments at up to 1.2 km stand-off distances, in day and night conditions, are shown. The impact of background light, and how this is handled by changing the aperture stop size, is considered. Signal processing techniques to go from scattered photon detections via 3D point clouds to voxel-based scene analysis are described. The results support the position that single-photon counting with GmAPD arrays is suitable for 3D imaging in military applications with kilometer stand-off distances.