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Motivation for Work • Develop VIS-LWIR scene simulation – Realistic levels of clutter •Spectral •Spatial – Easy user control of terrain materials •Reflectance in Visible-MWIR (NASA SBIR) •Emissivity/Temperature in MWIR-LWIR •Statistical terrain definition – Incorporate digital elevation maps – 3D variable atmosphere – 3D complex cloud fields – 3D faceted objects • Simulation tool used to test algorithms – Atmospheric compensation – Object detection – Scene classification/segmentation – Sensor development • Simulations to supplement data collects – Data usually collected on high visibility days – Simulate low visibility & bad weather Full Optical Spectrum Hyperspectral Scene Simulation Robert Sundberg and Steven Richtsmeier Spectral Sciences, Inc., Burlington, MA Raymond Haren AFRL/SNJT, Wright-Patterson AFB, OH 50 km uniform boundary 15-50 km 100 m layers 0-15 km (100 m) voxels 3 (1 m) pixels 2 100 m Atmospheric profile Exit to Space Backward Photon Trajectory Atmospheric Scattering Surface Scattering Sum Solar Scatter Probabilities • Unified UV to LWIR RT • 3D atmospheres with complex clouds • 3D surfaces with BRDF’s (DEM) • 3D object insertion • 3D plume model • MODTRAN optical properties, profiles, and spectroscopy • Extended to underwater imaging • Active illumination sources (LIDAR) MCScene Spectral Scene Simulation Validation MCScene Summary • New 3D code for computing visible to LWIR HSI/MSI data cubes • Spectral/spatial clutter with statistical behavior similar to nature • Applicable to wide variety of remote sensing problems • MCScene team – SBIR & STTR funding •AFRL/SNJT phase I/II/II+ •NIMA phase I/II •NASA phase I •US Army phase I – IRAD funding •Spectral Sciences, Inc. – Industrial partners •Kodak •Research Systems, Inc. •Rochester Institute of Technology • Direct sun-ground-sensor term calculated explicitly • Weighting factor for molecular absorption • Integrate thru 3D world in steps • Sample probability distributions for distance traveled and scattering directions • Atmospheric scattering (1 st order) ω, Single scattering albedo P(θs), Scattering phase function 0.0 0.2 0.4 0.6 0.8 1.0 0.250 0.275 0.300 0.325 0.600 0.625 0.650 0.675 # = 0.800 #= 0.975 EXACT 10 4 PHOTONS 10 6 PHOTONS Apparent Reflectance ( " I/ μ F Cosine Solar Zenith (μ) 500 1000 1500 2000 2500 -0.02 0.00 0.02 0.04 0.2 0.4 0.6 0.8 Multiple Scattering Residuals Multiple Scattering Only Total MODTRAN4 w/ DISORT16 MOD4 w/ Cor- & DISORT 16 k Monte-Carlo 500 1000 1500 2000 2500 -0.02 0.00 0.02 0.04 0.2 0.4 0.6 0.8 !gnd=1 APPARENT REFLECTANCE WAVELENGTH (nm) 500 1000 1500 2000 2500 -0.006 -0.003 0.000 0.003 0.05 0.10 0.15 0.20 0.25 Multiple Scattering Residual Multiple Scattering Only Single + Multiple Scattering 500 1000 1500 2000 2500 -0.006 -0.003 0.000 0.003 0.05 0.10 0.15 0.20 0.25 !gnd=0 APPARENT REFLECTANCE WAVELENGTH (nm) MODTRAN4 w/ DISORT16 Monte-Carlo Cloud Scattering Details Data Driven Scene Simulation Download DEM Radiance Cube Correct with FLAASH Deshadow Register DEM & source reflectance MCScene Pre-calculate MODTRAN atmospheres Specify Sun and Sensor Generate Cloud Field Simulation Flow Chart Radiance Reflectance Shadow Map De-shadowed Radiance • Atmospheric Compensation –FLAASH –ELM 10 m USGS DEM Unit Reflectance DEM Image Sample Visible Image Sample LWIR Image • AVIRIS Scene – Virgin Mts., NV – 20 km nadir view – Solar geometry •28° Zenith •317° Azimuth – Composition Simple 3D Cloud Simulations Self Shadow Major Features 1 km Cloud Over Dark Vegetation Atmospheric Shadow Ground Shadow 200 m τc=5 0 100 200 300 400 500 0.0 0.2 0.4 0.6 0.8 1.0 Cloud Self Shadow Cloud Shadow Soil Cloud 0.65μm 0.55μm 0.44μm Radiance ( μ W cm -2 sr -1 / cm -1 ) Image Diagonal Pixel 24500 24600 24700 24800 24900 25000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Shadow Line Cloud 0.1km Thick Region 0.2km Thick Region CLOUD BASE 7.8km 4.8km 1.8km Apparent Reflectance ( ! I/ μ sun F sun Pixel (meters) Realistic Scene Generation Initialize photon position and view direction Trace path optical depth, ! " = - ln Does path terminate within the atmosphere? Does path terminate at the ground? Photon exit. Photon Next Sum solar scatter source term & update photon weight Sum solar scatter source term & update photon weight If trajectory is completed, Photon Next Sample scattering phase function for new direction Sample surface BRDF for new direction If trajectory is completed, Photon Next Photon Trajectory Flow Chart () () () s cld cld s aer aer s Ray Ray P P P P ! " ! " ! " " + + # ( ) 2 3 2 2 ) cos 2 1 ( 4 1 ; s s G H g g g g P ! " ! # + # = # ( ) 2 2 ) 1 ( 2 ) 2 ( ) 1 ( 2 2 cos g g g g g G H s ! ! ! ! " + # + + + + = # Phase Function Form & Sampling () dT T P sun s T sun a g ! " μ # $ % = 1
