KEYWORDS: Solar radiation models, Sensors, Image sensors, Ray tracing, Monte Carlo methods, Data modeling, Visualization, Solar radiation, Radiative transfer, Prototyping
Computational modeling of spectral and hyperspectral imagery can be performed using radiative flux calculations on highly resolved geometric models. Faceted geometry models are both memory intensive and computationally expensive but allow for a fine-grained approach to radiative modeling. Using high resolution faceted geometry, improved synthetic imagery can be generated from a ray casting sensor model. This paper describes the results of a distributed memory ray tracing architecture for processing high facet count geometry that is capable of modeling radiative flux for highly resolved landscapes. Monte Carlo integration of the radiative transfer equation is coupled with a soil heat transfer model to facilitate solving for temperatures. Ray tracing procedures then use material properties to communicate radiative flux back to a sensor model. Emitted radiation along with mid-wave radiation reflected from neighboring facets and reflected short-wave solar radiation is computed and returned for rays cast from a sensor model. Radiative results of a prototype rainforest have been acquired that demonstrate the modeling capability of the architecture for geometries exceeding 40 million facets. Images of individual spectral components visually validate the legitimacy of the flux simulation. This paper presents an architecture that has been developed with the potential to produce quality synthetic spectral data based on modeling of actual temperature and radiative flux.
Artificial intelligence and machine learning algorithms for object detection in the infrared require an extensive amount of high-resolution object-tagged thermal infrared images. Often, acquiring real imagery of sufficient size and range of environmental conditions is difficult due to the cost and time. To address this need, the current study has developed a novel computational framework, i.e. the Sensor Engine, that generates target-tagged synthetic infrared imagery of large complex natural environments. This computational framework, coupled with high-fidelity soil and vegetation thermal physics and geometry models, generates synthetic, high-definition infrared images tailored for High-Performance Computing (HPC) systems. A unique plugin mechanism used to load and unload configured infrared sensors at run time in addition to allowing the framework to effectively work with different sensors in parallel is also discussed. The sensor model within the Sensor Engine communicates with another computational framework to acquire radiative energy for each sensor pixel detector as well as material, distance, source location, and incident angle. To demonstrate the modus operandi of this computational framework, an evaluation and discussion of runtime message passing and test cases are provided.
For realistic synthetic imagery, radiative transfer methods coupled with large mesh geometry provide the most scientifically accurate way to model a scene. Radiative models typically use ray-tracing techniques to determine where radiative energy is coming from or moving to. This work presents an approach to making a ray query Geometry Engine that actively stores large-scale, terabyte-sized geometry in out-of-core memory on parallel general purpose processors. Procedures for geometry distribution, structures for efficient ray-tracing, and the ray query API are discussed. Geometry distribution uses Morton codes with parallel sorting routines to create geometry scene-chunks that are distributed among processing nodes. Each scene chunk is then broken down using a bounding volume hierarchy (BVH) using axis-aligned bounding boxes (AABB). The BVH allows for efficient ray tracing of the geometry. The ray query engine API allows client-side programs, such as sensor models and radiative transfer models, which exist on the same high performance computer to efficiently identify intersected geometry given directed rays and collect individual geometry elements. The geometry has key values that can uniquely identify data from solver programs. Scalability, partition timing, and ray timing results are presented.
It is well established that object recognition by human perception and by detection/identification algorithms is confounded by false alarms (e.g., [1]). These false alarms often are caused by static or transient features of the background. Machine learning can help discriminate between real targets and false alarms, but requires large and diverse image sets for training. The potential number of scenarios, environmental processes, material properties and states to be assessed is overwhelming and cannot practically be explored by field/lab collections alone. High-fidelity, physics-based simulation can now augment training sets with accurate synthetic sensor imagery, but at a high computational cost. To make synthetic image generation practical, it should include the fewest processes and coarsest spatiotemporal resolution needed to capture the system physics/state and accomplish the training.
Among the features known or expected to generate false alarms are: (1.) soil/material variability (spatial heterogeneity in density, mineral composition, reflectance), (2.) non-threat objects (rocks, trash), (3.) soil disturbance (physical and spectral effects), (4.) soil processes (moisture migration, evaporation), (5.) surface hydrology (rainfall runoff and surface ponding), (6.) vegetation processes (transpiration, rainfall interception and evaporation, non-saturating rain events, multi-layer canopy, (including thatch), discrete versus parameterized vegetation), and (7.) energy reflected or emitted by other scene components. This paper presents a suite of computational tools that will allow the community to begin to explore the relative importance of these features and determine when and how individual processes must be included explicitly or through simplifying assumptions/parameterizations. The justification for this decision to simplify is driven ultimately by the performance of a detection algorithm with the generated synthetic imagery. Knowing the required level of modeling detail is critical for designing test matrices for building image sets capable of training improved algorithms.
A related consideration in the creation of synthetic sensor imagery is validation of these complex, coupled modeling tools. Very few analytical solutions or laboratory experiments include enough complexity to thoroughly test model formulations. Conversely, field data collection cannot normally be characterized and measured with sufficient spatial and temporal detail to support true validation. Intermediate-scale physical exploration of near surface soil and atmospheric processes (e.g., Trautz et al., [2]) offers an alternative that is intermediary to the laboratory column and field scales. This allows many field-scale-dependent processes and effects to be reproduced, manipulated, isolated, and measured within a well characterized and controlled test environment at requisite spatiotemporal resolutions in both the air and soil.
KEYWORDS: Thermography, Infrared radiation, Solar radiation models, Monte Carlo methods, Wind energy, Solar energy, Shortwaves, Thermal modeling, Atmospheric modeling, 3D modeling
We describe the development of a centimeter-scale resolution simulation framework for a theoretical tree canopy that includes rainfall deposition, evaporation, and thermal infrared emittance. Rainfall is simulated as discrete raindrops with specified rate. The individual droplets will either fall through the canopy and intersect the ground; adhere to a leaf; bounce or shatter on impact with a leaf resulting in smaller droplets that are propagated through the canopy. Surface physical temperatures are individually determined by surface water evaporation, spatially varying within canopy wind velocities, solar radiation, and water vapor pressure. Results are validated by theoretical canopy gap and gross rainfall interception models.
KEYWORDS: Sensors, Electro optical modeling, Atmospheric modeling, RGB color model, Data modeling, 3D modeling, Vegetation, Mid-IR, General packet radio service, Systems modeling
The U.S. Army Engineer Research and Development Center (ERDC) developed a near-surface computational testbed
(CTB) for modeling geo-environments. This modeling capability is used to predict and improve the performance of
current and future-force sensor systems for surface and near-surface threat detection for a wide range of geoenvironments.
The CTB is a suite of integrated models and tools used to approximately replicate geo-physical processes
such as radiometry, meteorology, moisture transport, and thermal transport that influence the resultant signatures of both
natural and man-made materials, as perceived by the sensors. The CTB is designed within a High Performance
Computing (HPC) framework to accommodate the size and complexity of the virtual environments required for
analyzing and quantifying sensor performance. Specifically, as a rule-of-thumb, the size of the scene should encompass
an area that is at a minimum, the size of the spatial coverage of the sensor. This HPC capability allows the CTB to
replicate geophysical processes and subsurface heterogeneity with high levels of realism and to provide new insight into
identifying the geophysical processes and environmental factors that significantly affect the signatures sensed by
multispectral imaging, near-infrared, mid-wave infrared, long-wave infrared, and ground penetrating radar sensors.
Additionally, this effort is helping to quantify the performance and optimal time-of-use for sensors to detect threats
within highly heterogeneous geo-environments by reducing false alarms from automated target recognition algorithms.
Soil moisture conditions have an impact upon virtually all aspects of Army activities and are increasingly affecting its
systems and operations. Soil moisture conditions affect operational mobility, detection of landmines and unexploded
ordinance, natural material penetration/excavation, military engineering activities, blowing dust and sand, watershed
responses, and flooding. This study further explores a method for high-resolution (2.7 m) soil moisture mapping using
remote satellite optical imagery that is readily available from Landsat and QuickBird. The soil moisture estimations are
needed for the evaluation of IED sensors using the Countermine Simulation Testbed in regions where access is difficult
or impossible. The method has been tested in Helmand Province, Afghanistan, using a Landsat7 image and a QuickBird
image of April 23 and 24, 2009, respectively. In previous work it was found that Landsat soil moisture can be predicted
from the visual and near infra-red Landsat bands1-4. Since QuickBird bands 1-4 are almost identical to Landsat bands 1-
4, a Landsat soil moisture map can be downscaled using QuickBird bands 1-4. However, using this global approach for
downscaling from Landsat to QuickBird scale yielded a small number of pixels with erroneous soil moisture values.
Therefore, the objective of this study is to examine how the quality of the downscaled soil moisture maps can be
improved by using a data stratification approach for the development of downscaling regression equations for each
landscape class. It was found that stratification results in a reliable downscaled soil moisture map with a spatial
resolution of 2.7 m.
Soil moisture conditions have an impact upon virtually all aspects of Army activities and are increasingly affecting its
systems and operations. Soil moisture conditions affect operational mobility, detection of landmines and unexploded
ordinance, military engineering activities, blowing dust and sand, watershed responses, and flooding. This study explores
a novel method for high-resolution (2.7 m) soil moisture mapping using remote satellite optical imagery that is readily
available from Landsat and QuickBird. The soil moisture estimations are needed for the evaluation of sensors for
Improvised Explosive Devices (IEDs) using the Countermine Simulation Test Bed in regions where access is denied.
The method has been tested in Helmand Province, Afghanistan, using a Landsat7 and a QuickBird image of April 23 and
24, 2009, respectively. The first implementation of the method yielded promising results.
Thermal infrared signatures of natural landscapes can vary greatly temporally and spatially. In our research, we describe our preliminary results of the spatial variability of vegetation thermal infrared signatures and vegetation density in a mid-western test minefield characterized by a linear PAR (Photosynthetically Active Radiation) ceptometer and ground-based laser radar. The linear PAR ceptometer consists of a probe about 80-cm long that contains 80 photodiodes that are sensitive to the PAR waveband. The probe calculates leaf area index (LAI, projected leaf area per unit ground area) based on sun zenith angle, leaf angle distribution, and fraction of solar beam radiation. For the 50-m by 175-m test area, the vegetation leaf area index varied from 0.1 to 4.8 and laser measured vegetation height ranged from 0.1-m to 1.9-m. The high-resolution laser radar data are used to estimate high-resolution leaf area index from the coarse PAR ceptometer measurements. These data, combined with local meteorological data, are then used to model the spatial (0.5-m) distribution of surface heat flux under a vegetation canopy.
This paper describes the high temporal (1 sec to 5 min) and spatial thermal infrared directional characterization of low dense grass canopy during high humidity conditions to study the diurnal and spatial variation of simple vegetation background signatures. The instruments used in the characterization effort consisted of two infrared cameras (8-14 μm) set at nadir and 45 degrees, four sets of radiometers (3-5 μm and 8-12 μm), micrometeorological instruments, and thermocouples placed within the grass. Micrometeorological measurements included wind speed, air temperature, and relative humidity observed at several heights above the canopy sampling occurred at 1 sec and 5 min intervals. These measurements were used to calculate wind speed, air temperature, and relative humidity profiles down to the top of the grass canopy.
Analysis of the measured thermal images consists of quantifying the diurnal thermal differences in the directional background signatures, directional thermal variance, and thermal variance differences related to observation angle, solar radiation, and wind speed. These preliminary analyses indicate that for this environment, measurements at large temporal scales, the thermal variance is primarily affected by solar radiation, but at small temporal scales turbulent mixing of fluxes becomes the more dominant cause of the variance.
In this paper, we present our first results towards understanding high temporal frequency thermal infrared response from a dense grass canopy. The model is driven by slowly varying, time-averaged meteorological conditions and by high frequency measurements of local and within canopy profiles of relative humidity and wind speed, and compared to high frequency thermal infrared observations. Previously, we have employed three-dimensional ray tracing to compute the intercepted and scattered solar and IR radiation fluxes and for final scene rendering. For the turbulent fluxes, simple resistance models for latent and sensible heat with one-dimensional profiles of relative humidity and wind speed are used. Our modeling approach has proven successful in capturing the directional and diurnal variation in background thermal infrared signatures. We hypothesize that at these scales, where the model is typically driven by time-averaged, local meteorological conditions, the primary source of thermal variance arises from the spatial distribution of sunlit and shaded foliage elements within the canopy and the associated radiative interactions.
In recent experiments, we have begun to focus on the high temporal frequency response of plant canopies in the thermal infrared at 1 sec to 5 min intervals. At these scales, we hypothesize turbulent mixing plays a more dominant role. Our results indicate that in the high frequency domain, the vertical profile of temperature change is tightly coupled to the within canopy wind speed. In the results reported here, the canopy cools from the top down with increased wind velocities and heats from the bottom up at low wind velocities.
Laser profilometers hold the promise of improving smart munition detection and aimpoint selection performance when combined with data from other sensor types, such as passive thermal infrared. The high cost of physically testing sensor systems dictates that simulation should be used whenever possible. This paper describes the development and preliminary verification of a profilometer simulation developed as part of a larger smart munition sensor simulation model. A single-scattering laser profilometer model, which predicts returns from passive illumination sources, such as the sun and sky, in addition to laser returns, is formulated and implemented. Several simple scenarios are simulated to test model behavior as a function of environmental illumination, reflecting material, and target geometry. Results agree with expectations and show the importance including environmental conditions and detailed material reflective properties in the model.
This paper describes the methodology for executing real-time simulations for the support of field testing of smart munition sensors. The sensor simulated is a dual-mode sensor using passive thermal infrared and active laser profiling. The types of tests supported by the simulation are dynamic flight tests over stationary targets, captive flight tests with moving tactical targets, and end-to-end system tests with dynamic flight over moving tactical targets. The components of this methodology that will be discussed include the sensor simulation model, target and background models, and measurement procedures for generating inputs required for target and background models. The resulting simulation capability can be used to support a wide range of evaluations including concept evaluation, subsystem design trade-off analysis, and system performance evaluation.
KEYWORDS: 3D modeling, Reflectivity, Solar radiation models, Alternate lighting of surfaces, Atmospheric modeling, Data modeling, Spectroscopy, Photography, Atmospheric corrections, Sensors
This paper describes our hyperspectral reflectance modeling of a forest canopy based on measured input parameters and comparison with Earth Observing - 1 (EO-1) Advanced Land Imager (ALI) and Hyperion data. The model uses a high resolution, three-dimensional (3D) ray-tracing approach to estimate the intercepted and scattered solar radiation at multiple narrow wavelength bands. We present the comparisons of the effects of woody biomass, leaf litter, and clumping on reflectance signatures. The experimental data used for the model were collected in a hardwood forest canopy in Rochester, New York. Model calculations also are compared to a more simplified, low-resolution 3D model and a simple, multi-layer differential equation model.
Data assimilation methods applied to hydrologic models can incorporate spatially distributed maps of near surface temperature, especially if such measurements can be reliably inferred from satellite observations. Uncalibrated thermal IR imagery sometimes is scaled to temperature units to obtain such observations using the assumption that dense forest canopies are close to air temperature. For fully leafed deciduous forest canopies in the summer, this approximation is usually valid within 2C. In a leafless canopy, however, the materials views are thick boles and branches and the forest floor, which can store heat and yield significantly higher variations. Winter coniferous forests are intermediate with needles and branches being the predominant viewed materials. The US Dept of Energy's Multispectral Thermal Imager (MTI) is an experimental satellite with the capability to perform quantitative scene measurements in the reflective and thermal infrared region respectively. Its multispectral thermal IR capability enables quantitative surface temperature retrieval if pixel emissivity is known. MTI is pointable and targets multiple times in the winter and spring of 2001 at the Howland, Maine AmeriFlux research site operated by the University of Maine. Supporting meteorological and optical depth measurements also were made from three towers at the site. Directional thermal models of forest woody materials and needles are driver by the surface measurements and compared to satellite data to help evaluate the relationship between air temperature and satellite thermal measurements as a function of look angles, day and night.
This paper describes the integration of a verified and validated (V&V) smart munition model for the Army's Hornet sublet into OneSAF Testbed Baseline for equipment performance simulation, testing, and training. This effort improves realism of current Hornet behavior in the Testbed by implementing sublet fly-out to model the effects of target type, speed, and environmental conditions on target acquisition. Also addressed are issues of maintaining a V&V of the model and at the same time reducing fidelity of the model to obtain real-time simulation of the sublet fly-out and target acquisition.
Satellite observations of agricultural and other plant canopies in the thermal IR regime have generally been at spatial scales of tens to hundreds of meters. Use of the thermal IR at higher resolutions is confounded by the mixture problem and other associated scaling issues. Advances in sensor technology will extend our capabilities for IR measurements to shorter wavelengths and yield improved spatial resolutions. However, experience with aircraft remote sensing observations has indicated that care must be exercised in understanding the interaction effects of viewing geometry at these higher resolutions. The utilization and scaling of observables with multi-resolution remote sensing data sets remain a difficult problem. At high spatial resolution the three-dimensional character of scene components contained within a pixel must be considered. In this paper, we explore the variability in brightness temperature and the co-variation of NDVI with brightness temperature as a function of viewing geometry and changing spatial resolution. Using three- dimensional models for both canopy reflectance and thermal IR exitance, we employ a theoretical analysis for an agricultural scene where previous comparisons and measurements were available.
KEYWORDS: Sensors, Detection and tracking algorithms, Infrared sensors, Monte Carlo methods, Temperature metrology, Vegetation, Sensor performance, 3D modeling, Thermography, Data modeling
Using synthetic background scenes in the modeling of thermal infrared sensor-based smart munitions offers tremendous flexibility in exploring the performance envelope of these systems. However, to reach this goal, the synthetic background generation process must undergo the scrutiny of verification and validation to be accredited for use with a specific sensor system. Traditional approaches to validating synthetic scenes range from low-level subjective comparison to absolute pixel-to-pixel agreement between the two scenes. Neither of these approaches considers the specific smart munition sensor and processor which ultimately use the scene. In this paper we present an alternate validation approach based on comparison between end performance of a thermal infrared sensor-based smart munition system using synthetic/real scene pairs. Paired synthetic/real thermal scenes, including a low and a high-clutter level, are compared with conventional validation metrics and with the performance-based metric, using various smart munition sensor targeting algorithms. The degree of scene fidelity (absolute agreement between scene pairs) required to replicate performance varies with clutter level and processor algorithm. Under high clutter conditions, greater synthetic scene fidelity is required to match performance.
We present a simple, three-dimensional vegetation canopy thermal infrared exitance model for agricultural scenes. Computer graphics and ray-tracing techniques are used to estimate three-dimensional canopy view factors and scene shadows. The view factors are used to weight the individual contributions of soil and vegetation emission computed by steady-state energy budget formulations. We compare the three- dimensional model results to a one-dimensional formulation for an agricultural test site from the Hydrologic Atmospheric Pilot Experiment and Modelisation du Bilan Hydrique. The root mean square error is daylight brightness temperature for the one dimensional model was 2.5 degrees Celsius and 2.0 degrees Celsius for the three dimensional model.
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