Employing a modified photon mapping technique that originated within the computer graphics community, a first-principle
based elastic LIDAR model was developed within the Digital and Remote Sensing Image Generation
(DIRSIG) framework that calculates time-gated photon counts at a sensor from topographic reflections and multiply
scattered returns. The LIDAR module handles a wide variety of complicated scene geometries, diverse surface and
participating media optical characteristics, multiple bounce and multiple scattering effects, and a variety of source and
sensor models. This flexible modeling environment allows the researcher to evaluate sensor design trades for
topographic systems and the impact that scattering constituents (e.g. water vapor, dust, sediment, soot, etc.) could have
on a Differential Absorption LIDAR (DIAL) system's ability to detect and quantify constituents of interest within
volumes including water and atmospheric plumes. This paper will present the numerical approaches employed to
predict sensor reaching photon counts including specific approaches adopted to model multiple scattering and
absorption within a plume. These approaches will be discussed and benchmarked against analytically predicted results
using a non-stationary, diffusion approximation and a multiple scattering LIDAR equation. The analytical development
and consistency of the modified photon mapping method with the underlying physics and radiative transfer theory for
participating media is also presented. A representative dataset generated by DIRSIG of a DIAL system will be presented
and analyzed for a synthetic scene containing a factory stack plume containing absorption and scattering effluents.
KEYWORDS: Sensors, LIDAR, Systems modeling, Data modeling, Atmospheric modeling, Time correlated photon counting, Scattering, Photon counting, 3D modeling, RGB color model
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 multi- and 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 paper will present the numerical approaches employed to predict sensor reaching radiances and
comparisons with analytically predicted results. Representative data sets generated by the DIRSIG model for a topographical LIDAR will be shown. Additionally, the results from phenomenological case studies including standard terrain topography, forest canopy penetration, and camouflaged hard targets will be presented.
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