Three dimensional imaging is a powerful tool for object detection, identification, and classification. 3D imaging allows
removal of partial obscurations in front of the imaged object. Traditional 3D image sensing has been Laser Radar
(LADAR) based. Active imaging has benefits; however, its disadvantages are costs, detector array complexity, power,
weight, and size. In this keynote address paper, we present an overview of 3D sensing approaches based on passive
sensing using commercially available detector technology. 3D passive sensing will provide many benefits, including
advantages at shorter ranges. For small, inexpensive UAVs, it is likely that 3D passive imaging will be preferable to
active 3D imaging.