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Time-gated LIDAR Scene Simulation

The Digital Imaging and Remote Sensing Image Generation (DIRSIG) model has been developed at the Rochester Institute of Technology (RIT) for over a decade. The model is an established, first-principles based scene simulation tool that has been focused on passive multiand hyper-spectral sensing from the visible to long wave infrared (0.4 to 14 μm). Leveraging photon mapping techniques utilized by the computer graphics community, a first-principles based elastic Light Detection and Ranging (LIDAR) model was incorporated into the passive radiometry framework so that the model calculates arbitrary, time-gated radiances reaching the sensor for both the atmospheric and topographic returns. The active LIDAR module handles a wide variety of complicated scene geometries, a diverse set of surface and participating media optical characteristics, multiple bounce and multiple scattering effects, and a flexible suite of sensor models. This presentation will cover the numerical approaches employed to predict sensor reaching radiances and comparisons with analytically predicted results. The interest in modeling Differential Absorption LIDAR (DIAL) sensor engagements involving participating medium such as gaseous plumes presented significant challenges that were overcome using the photon mapping modeling paradigm. Specific approaches adopted to model the multiple scattering and absorption within the plume will be discussed. Currently, the DIRSIG LIDAR model is undergoing a rigorous verification and validation effort including benchmarking the single and multiple scattering predictions for a participating medium against a discrete ordinate method radiative transfer algorithm (DISORT). The preliminary results and status will be presented along with the near-term path forward. Representative datasets generated via DIRSIG for both a topographical LIDAR and a simple DIAL system will be shown. Additionally, the results from phenomenological case studies including standard terrain topography, forest canopy penetration, plume interrogation, and camouflaged hard targets will be presented. About the Presenter: Daniel Blevins received his B.S. in electrical engineering from Wright State University in 1994 and a M.S. in electrical engineering from the University of Michigan in 2000. He has served over 11 years in the United States Air Force in a variety of technical and management roles, with a principal focus on technical intelligence exploitation and development of space-based and airborne imaging sensors. His ongoing research at the Chester F. Carlson Center for Imaging Science is focused on confirming through physics-based modeling approaches that obscurants, even as simple as water vapor and soot, do indeed significantly alter the observable signatures of gaseous plumes for a DIAL engagement, and in a qualitative fashion, attempt to identify the impact on the chemical detection sensitivity of sample system designs when in the possible presence of intentional or natural interfering chemicals. The continuing development and verification of the DIRSIG LIDAR model is a critical component to his research and the primary means of investigation at this time.