So far, the utilization of shadows and silhouettes in laser imaging and mapping has been limited. On the contrary, for Synthetic Aperture Radars (SAR) and Sonars (SAS), shadows are important observables for target detection, location, tracking and even identification. Compared to SAR systems, however, direct detection laser systems offer no restrictions on shadow degradation due to platform and target movements and diffraction effects. This means that the shape of the shadow can be directly related to the shape of the target if the illumination geometry and background behind the target are known. This paper will review some of the shadow characteristics for both SAR, SAS and laser radar. Examples of shadows from different type of laser imaging and mapping system will be presented. Finally different type of laser sensors are discussed in relation to shadow generation for target detection and classification.

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Ove Steinvall, Lars Sjökvist, Per Jonsson, and Sten Edström, "Shadows in laser imaging and mapping," Proc. SPIE 10796, Electro-Optical Remote Sensing XII, 1079609 (Presented at SPIE Security + Defence: September 12, 2018; Published: 9 October 2018); https://doi.org/10.1117/12.2325118.