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Scattering Effect Contributions to the Directional Canopy Emissivity and Brightness Temperature Based on CE-P and CBT-P Models
摘要： The directional anisotropy of canopy emissivity and brightness temperature in the thermal infrared band has widely been studied. However, the contribution of different scattering orders has been an open scientific question for many years. The recently proposed CE-P model enables us to analytically evaluate the different scattering orders. Herein, we derive expressions for the first double collisions (DCE12) and first triple collisions (DCE123). Our result shows that DCE123 can simulate the observed emissivity with an error less than 0.001 and that DCE12 is reasonably accurate when leaf emissivity is greater than 0.96. Numerical analysis shows that the contribution of quadruple or greater collisions can be ignored when the leaf (soil) emissivity is no less than 0.90. Furthermore, we develop the CBT-P model to simulate the directional brightness temperature (DBT) based on the new optimized CE-P model (DCE123) and validate it by 4SAIL (4-Stream Radiative Transfer Theory of Scattering by Arbitrary Inclined Leaves) and DART (Discrete Anisotropic Radiative Transfer) models. Both of isothermal (soil temperature is equal to leaf temperature) and nonisothermal (soil temperature is higher than leaf temperature) cases are considered. The maximum differences between the CBT-P model and 4SAIL (DART) are less than 0.35 K (0.42 K), the average differences between CBT-P and 4SAIL (DART) are less than 0.10 K (0.13 K), and the R2 is over 0.99 (0.95) with component emissivities larger than 0.90 and the difference between soil and leaf temperatures less than 20 K. The directional anisotropy of DBT is dominated by the zero-scattering and the single scattering terms according to the new developed CBT-P model.
关键词： directional canopy emissivity (DCE),CBT-P,Discrete Anisotropic Radiative Transfer (DART),4-Stream Radiative Transfer Theory of Scattering by Arbitrary Inclined Leaves (4SAIL),CE-P,directional brightness temperature (DBT)
更新于2025-09-23 15:23:52
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Modeling of Radiative Properties of Polystyrene Foams Containing IR-Opacifiers
摘要： The addition of opacifiers in foams considerably reduces the radiative thermal conductivity and consequently enhances the insulation performance of the foams. In this work two different methods were developed to calculate the spectral specific extinction coefficient of opacified extruded polystyrene (XPS) foam material. Cell morphology and thermal conductivity of two identical XPS-foams, one opacified with 3 wt% carbon black as opacifier and one without opacifier, were thoroughly characterized. The experimental results were in a good agreement with the theoretical results obtained from two different computing techniques. These methods allow a good prediction of the specific extinction coefficient of arbitrary opacified foam material.
关键词： Radiative transfer,Radiative thermal conductivity,Complex refractive index,Extinction coefficient,Porous materials,Opacifiers
更新于2025-09-23 15:23:52
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An Interplay between Photons, Canopy Structure, and Recollision Probability: A Review of the Spectral Invariants Theory of 3D Canopy Radiative Transfer Processes
摘要： Earth observations collected by remote sensors provide unique information to our ever-growing knowledge of the terrestrial biosphere. Yet, retrieving information from remote sensing data requires sophisticated processing and demands a better understanding of the underlying physics. This paper reviews research efforts that lead to the developments of the stochastic radiative transfer equation (RTE) and the spectral invariants theory. The former simplifies the characteristics of canopy structures with a pair-correlation function so that the 3D information can be succinctly packed into a 1D equation. The latter indicates that the interactions between photons and canopy elements converge to certain invariant patterns quantifiable by a few wavelength independent parameters, which satisfy the law of energy conservation. By revealing the connections between plant structural characteristics and photon recollision probability, these developments significantly advance our understanding of the transportation of radiation within vegetation canopies. They enable a novel physically-based algorithm to simulate the 'hot-spot' phenomenon of canopy bidirectional reflectance while conserving energy, a challenge known to the classic radiative transfer models. Therefore, these theoretical developments have a far-reaching influence in optical remote sensing of the biosphere.
关键词： vegetation remote sensing,stochastic radiative transfer equation,spectral invariants theory
更新于2025-09-23 15:23:52
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LESS: LargE-Scale remote sensing data and image simulation framework over heterogeneous 3D scenes
摘要： Three-dimensional (3D) radiative transfer modeling of the transport and interaction of radiation through earth surfaces is challenging due to the complexity of the landscapes as well as the intensive computational cost of 3D radiative transfer simulations. To reduce computation time, current models work with schematic landscapes or with small-scale realistic scenes. The computer graphics community provides the most accurate and efficient models (known as renderers) but they were not designed specifically for performing scientific radiative transfer simulations. In this study, we propose LESS, a new 3D radiative transfer modeling framework. LESS employs a weighted forward photon tracing method to simulate multispectral bidirectional reflectance factor (BRF) or flux-related data (e.g., downwelling radiation) and a backward path tracing method to generate sensor images (e.g., fisheye images) or large-scale (e.g. 1 km2) spectral images. The backward path tracing also has been extended to simulate thermal infrared radiation by using an on-the-fly computation of the sunlit and shaded scene components. This framework is achieved through the development of a user-friendly graphic user interface (GUI) and a set of tools to help construct the landscape and set parameters. The accuracy of LESS is evaluated with other models as well as field measurements in terms of directional BRFs and pixel-wise simulated image comparisons, which shows very good agreement. LESS has the potential in simulating datasets of realistically reconstructed landscapes. Such simulated datasets can be used as benchmarks for various applications in remote sensing, forestry investigation and photogrammetry.
关键词： Landscape modeling,Image simulation,Radiative transfer
更新于2025-09-23 15:23:52
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Study of the effects of phytoplankton morphology and vertical profile on lidar attenuated backscatter and depolarization ratio
摘要： Propagation of a lidar beam in a coupled atmosphere-ocean model consisting of multiple atmospheric and upper oceanic layers and a rough ocean surface is studied by using a vectorized Monte Carlo radiative transfer solver optimized specifically for lidar-based remote sensing applications. The effects of assumed phytoplankton morphology variations and its vertical distribution on the lidar attenuated backscatter and depolarization ratio are studied. In this study, a phytoplankton particle is assumed to be a sphere, a sphere with a core, or a randomly distorted hexahedron with or without a core. The single-scattering properties of the nonspherical/inhomogeneous particles are computed using appropriate state-of-the-art light-scattering computational capabilities. Vertical variation of the phytoplankton distribution is derived explicitly using a PAR (photosynthetically active radiation) limited carbon biomass balance equation that is subsequently coupled with the Monte Carlo solver.
关键词： Radiative transfer,Lidar,Ocean optics,Monte Carlo,Phytoplankton,Net primary production,Remote sensing
更新于2025-09-23 15:23:52
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Mapping the thermal structure and minor species of Venus mesosphere with ALMA submillimeter observations
摘要： Context. Water vapor and sulfur compounds are key species in the photochemistry of Venus mesosphere. These species, together with mesospheric temperatures, exhibit drastic temporal variations, both on short timescales (diurnal and day-to-day) as well on long timescales, far from being understood. Aims. We targeted CO, SO, HDO and SO2 transitions in the submillimeter range using the Atacama Large Millimeter Array (ALMA) to study their spatial and temporal variations. Methods. Four sets of observations were acquired on different dates in November 2011 during the first ALMA Early Science observation Cycle 0. Venus angular diameter was about 11'' with an illumination factor of 92%, so that mostly the day side of the planet was mapped. Assuming a nominal CO abundance profile, we retrieved vertical temperature profiles over the entire disk as a function of latitude and local time. Temperature profiles were later used to retrieve SO, SO2, and H2O. We used HDO as a tracer for water assuming a D/H enrichment of 200 times the terrestrial value. Results. We derived 3D maps of mesospheric temperatures in the altitude range 70?105 km. SO, SO2, and H2O are characterized by a negligible abundance below ～85 km followed by an increase with altitude in the upper mesosphere. Disk-averaged SO abundances present a maximum mixing ratio of 15.0 ± 3.1 ppb on November 26 followed the next day by a minimum value of 9.9 ± 1.2 ppb. Due to a very low S/N, SO2 could only be derived from the disk-averaged spectrum on the first day of observation revealing an abundance of 16.5 ± 4.6 ppb. We found a SO2/SO ratio of 1.5 ± 0.4. Global maps of SO reveal strong variations both with latitude and local time and from day to day with abundance ranging from <1 to 15 ppb. H2O disk-averages retrievals reveal a steady decrease from November 14 to 27, with the abundance varying from 3.6 ± 0.6 ppm on the first day to 2.9 ± 0.7 ppm on the last day. H2O maps reveal a slightly higher abundance on the evening side compared to the morning side and a strong depletion between the first and the second day of observation.
关键词： planets and satellites: individual: Venus,methods: data analysis,planets and satellites: atmospheres,submillimeter: planetary systems,instrumentation: interferometers,radiative transfer
更新于2025-09-23 15:23:52
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Processing a New Hyperspectral Data Set for Target Detection and Atmospheric Compensation Algorithm Assessment: The RIT2017 Data Set
摘要： This paper introduces a new and challenging hyperspectral dataset to the remote sensing community called the 'RIT2017 Data Set' which can be used for the assessment of target detection algorithms. This dataset encompasses 90 targets in a background of up to 8 million pixels (or less if sub-setting). The same dataset can also be used for atmospheric compensation studies for it has identical sets of large panels in both the sun and full shadow. This paper briefly introduces the data collection campaign, the target objects, and addresses the radiometric fidelity of the imaging spectrometer data, which showed very good results. Lastly, the data is atmospherically compensated using an in-scene technique, which also showed fairly good results.
关键词： atmospheric compensation,physics-based modeling,hyperspectral imaging,target detection,radiative transfer
更新于2025-09-23 15:23:52
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A radiative transfer framework for non-exponential media
摘要： We develop a new theory of volumetric light transport for media with non-exponential free-flight distributions. Recent insights from atmospheric sciences and neutron transport demonstrate that such distributions arise in the presence of correlated scatterers, which are naturally produced by processes such as cloud condensation and fractal-pattern formation. Our theory formulates a non-exponential path integral as the result of averaging stochastic classical media, and we introduce practical models to solve the resulting averaging problem efficiently. Our theory results in a generalized path integral which allows us to handle non-exponential media using the full range of Monte Carlo rendering algorithms while enriching the range of achievable appearance. We propose parametric models for controlling the statistical correlations by leveraging work on stochastic processes, and we develop a method to combine such unresolved correlations (and the resulting non-exponential free-flight behavior) with explicitly modeled macroscopic heterogeneity. This provides a powerful authoring approach where artists can freely design the shape of the attenuation profile separately from the macroscopic heterogeneous density, while our theory provides a physically consistent interpretation in terms of a path space integral. We address important considerations for graphics including reciprocity and bidirectional rendering algorithms, all in the presence of surfaces and correlated media.
关键词： non-exponential transport,global illumination,participating media,volume rendering,radiative transfer
更新于2025-09-23 15:23:52
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Beamed Ly <i>α</i> emission through outflow-driven cavities
摘要： We investigate the radiative transfer of Lyα photons through simplified anisotropic gas distributions, which represent physically motivated extensions of the popular shell models. Our study is motivated by the notion that (i) shell models do not always reproduce observed Lyα spectral line profiles; (ii) (typical) shell models do not allow for the escape of ionizing photons; and (iii) the observation and expectation that winds are more complex, anisotropic phenomena. We examine the influence of inclination on the Lyα spectra, relative fluxes and escape fractions. We find the flux to be enhanced/suppressed by factors up to a few depending on the parameter range of the models, corresponding to a boost in equivalent width of the same amplitude if we neglect dust. In general, lower mean optical depths tend to reduce the impact of anisotropies as is expected. We find a correlation between an observed peak in the – occasionally triple-peaked – spectrum at the systemic velocity and the existence of a low optical depth cavity along the line of sight. This can be of importance in the search for ionizing photons leaking from high- redshift galaxies since these photons will also be able to escape through the cavity.
关键词： radiative transfer,galaxies: high-redshift
更新于2025-09-23 15:23:52
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Accounting for Static and Dynamic Open Water in the Modeling of SMAP Brightness Temperatures Over Peatlands
摘要： Hydrological change in peatlands due to anthropogenic disturbance and global warming can release enormous amounts of greenhouse gas emissions. Passive microwave satellite observations are an opportunity to globally monitor these changes. Abundant static and dynamic open water surfaces in peatlands strongly affect observed brightness temperatures (Tb). Here, we account for these contributions in radiative transfer modeling using NASA's Goddard Earth Observing System Model version 5 (GEOS-5) static open water mask and, for the dynamic open water fraction, the simulated inundated area using a version of the GEOS-5 Catchment land surface model that has been modified for peatland areas (PEAT-CLSM). Modeled Tb is compared against two years of SMAP L-band Tb. Preliminary results indicate: (i) a bias reduction when including the static open water fraction in a simple RTM mixing model, and (ii) significantly improved correlation between modeled and observed Tb when using land surface output from PEAT-CLSM instead of the operational CLSM.
关键词： organic soil,radiative transfer model,soil moisture,L-band,passive microwave
更新于2025-09-23 15:22:29